Thyroid Blood Tests: TSH, Free T4, Free T3, and Thyroid Antibodies

Thyroid blood tests evaluate pituitary signaling, circulating thyroid hormones, and selected autoimmune or monitoring markers. The TSH Test is usually the first laboratory test used to assess suspected primary thyroid dysfunction. The Free T4 Test helps classify an abnormal TSH result, while the Total T3 Test or Free T3 Test is most useful for selected low-TSH or hyperthyroid questions. Thyroid antibodies answer different autoimmune questions; they do not measure current thyroid function by themselves. Blood tests also cannot determine whether a thyroid nodule is benign or malignant. Results must be interpreted with symptoms, medications, supplements, pregnancy status, examination findings, and trends.^{1, 2, 3}

Important: This article is educational. It does not diagnose a thyroid disorder or replace medical care. Severe chest pain, fainting, marked shortness of breath, sudden confusion, severe weakness, a very rapid or irregular heartbeat, or urgent pregnancy-related concerns require prompt professional or emergency evaluation.

Part of the Ulta Lab Tests Knowledge Center

For an overview of specimens, individual tests, panels, screening, monitoring, and test selection, see The Complete Guide to Lab Tests and Blood Work. When reviewing reference intervals, flags, units, decision thresholds, and trends, use How to Read and Understand Your Lab Results. For ordering, preparation, specimen collection, and responsible follow-up, review Direct-Access Lab Testing: How It Works and What to Expect.

Thyroid questions often overlap with Metabolic Health, Weight Loss, and GLP-1 Monitoring, Women's Hormone Blood Tests, Men's Health Blood Tests, Fertility and Preconception Lab Tests, Vitamin and Nutrient Deficiency Tests, CBC and Anemia Blood Tests, Digestive Health Lab Tests, and Inflammation and Autoimmune Blood Tests.

On this page

• Key facts about thyroid blood tests
• What thyroid testing evaluates
• Symptoms, risk factors, and patient scenarios
• Thyroid symptoms and whole-body health patterns
• Thyroid testing tiers
• TSH-led test-selection framework
• Common thyroid laboratory patterns
• Pregnancy and postpartum considerations
• Individual tests versus panels
• Preparation and possible interference
• How to understand results
• Linked thyroid tests and panels
• Frequently asked questions

Key Facts About Thyroid Blood Tests

Test and quick facts	What it shows and how it is used	Preparation, influences, and limitations
TSH Test Use status: Common or first-line Specimen: Blood, commonly serum	Measures the pituitary signal to the thyroid. It is the preferred initial test for many questions about primary thyroid dysfunction.	Fasting is usually not required. Age, pregnancy, acute illness, pituitary disease, medications, collection timing, and assay interference can affect interpretation. A single result does not determine treatment.
Free T4 Test Use status: Common or first-line; monitoring Specimen: Blood, commonly serum	Measures unbound thyroxine. It helps classify an abnormal TSH pattern and is important when pituitary disease, pregnancy, or selected monitoring questions make TSH alone insufficient.	Medication timing, pregnancy, acute illness, binding changes, biotin, and assay method may influence the result.
Total T4 Test Use status: Risk-based or targeted Specimen: Blood, commonly serum	Measures bound and unbound thyroxine together. It can add context when pregnancy or binding-protein changes complicate free-hormone interpretation.	Estrogen exposure, pregnancy, liver or kidney conditions, illness, and binding-protein changes can alter total T4 without an equivalent change in thyroid function.
Total T3 Test or Free T3 Test Use status: Risk-based or targeted Specimen: Blood, commonly serum	May help assess selected low-TSH or hyperthyroid patterns, including situations in which T3 is elevated more than T4.	T3 testing usually adds little to routine hypothyroid evaluation. Binding proteins affect total T3, and free-hormone methods vary. Timing matters with T3-containing therapy.
Thyroid Peroxidase Antibodies Test Use status: Risk-based or targeted Specimen: Blood, commonly serum	Supports evaluation for autoimmune thyroid disease, especially Hashimoto's disease.	A positive result does not show whether thyroid hormone levels are currently high, low, or normal. Antibodies may be present before thyroid dysfunction develops.
Thyroglobulin Antibodies Test Use status: Risk-based, targeted, or specialist-directed Specimen: Blood, commonly serum	Adds autoimmune context and helps interpret thyroglobulin measurements used in selected thyroid-cancer follow-up.	It is not a thyroid-function test. Thyroglobulin antibodies can interfere with thyroglobulin measurement.
TRAb Test or TSI Test Use status: Risk-based, targeted, or monitoring Specimen: Blood, commonly serum	Supports Graves' disease evaluation and selected relapse, treatment, or pregnancy-risk questions.	These tests do not replace TSH, thyroid-hormone testing, examination, or imaging when indicated. Methods, units, and the antibody activity measured can differ.
Thyroglobulin Panel Test Use status: Specialist-directed monitoring Specimen: Blood, commonly serum	Used primarily for follow-up after defined treatment for differentiated thyroid cancer.	It is not a general screening test and is not used by itself to diagnose a new thyroid cancer. Interpretation depends on antibodies, remaining thyroid tissue, treatment history, imaging, method, and trend.
Calcitonin Test Use status: Specialist-directed Specimen: Blood, commonly serum	Used for selected evaluation or monitoring related to medullary thyroid cancer or familial risk.	It is not a broad thyroid-health or thyroid-cancer screening test. Noncancer causes can affect the result, so specialist context is important.

How common are thyroid disorders? Nearly 5 out of 100 Americans age 12 and older have hypothyroidism, although many cases are mild or have few obvious symptoms. About 1 out of 100 Americans age 12 and older have hyperthyroidism.^{18, 19} These population estimates do not mean that every nonspecific symptom requires thyroid testing; symptoms, risk, and the purpose of testing still matter.

What Thyroid Testing Evaluates

The thyroid is an endocrine gland in the lower front of the neck. It produces mostly thyroxine, or T4, and a smaller amount of triiodothyronine, or T3. The pituitary gland releases thyroid-stimulating hormone, or TSH, to regulate this system. Thyroid hormones influence energy use, heat production, heart rate, digestion, muscle function, reproductive health, growth, and brain function.^{1, 2}

Thyroid blood testing may be used for screening in defined populations, evaluating symptoms, supporting a diagnosis, identifying a suspected autoimmune cause, establishing a baseline, monitoring treatment, following pregnancy-related concerns, or monitoring selected patients after thyroid-cancer treatment. These are different purposes. A test that is appropriate for one purpose may be unnecessary or misleading for another.

Three Different Types of Thyroid Questions

Type of thyroid question	Examples and what it asks	What usually provides information
Thyroid function	Is the thyroid system producing too little or too much circulating hormone? Examples include primary hypothyroidism, hyperthyroidism, and some phases of thyroiditis.	TSH, Free T4, and selected Total T3 or Free T3 testing.
Autoimmune cause	Does the immune pattern support Hashimoto's disease or Graves' disease as a cause or risk context?	TPO antibodies, thyroglobulin antibodies, TRAb, or TSI, selected for the specific question. Antibodies do not replace function testing.
Thyroid structure	Is there a nodule, goiter, neck enlargement, inflammatory change, or a feature that raises concern for cancer?	Physical examination and thyroid ultrasound, with fine-needle aspiration when indicated. Blood tests can provide function or monitoring context but cannot classify a nodule as benign or malignant.8, 10, 11

What Laboratory Testing May Reveal and What It Cannot Reveal

What testing may help show	What it cannot establish by itself	What may be needed next
Whether pituitary signaling and circulating hormone measurements form a pattern consistent with primary hypothyroidism or hyperthyroidism.	The complete cause of fatigue, weight change, hair loss, palpitations, constipation, anxiety, or cognitive symptoms.	History, examination, medication review, targeted nonthyroid testing, and sometimes repeat testing.
Whether antibody results support an autoimmune cause such as Hashimoto's disease or Graves' disease.	Current thyroid function from antibody results alone, or whether every symptom is caused by autoimmunity.	TSH and thyroid-hormone results interpreted with the clinical setting.
Whether values are changing over time during treatment or follow-up.	Whether a medication should be started, stopped, or changed without professional interpretation.	Comparable collection conditions, prior results, diagnosis-specific targets, and the treating professional's plan.
Whether discordant results may need repetition, a different assay method, or laboratory consultation.	Why an unexpected result occurred without investigating interference, timing, illness, or uncommon disorders.	Repeat collection, another assay platform, interference studies, or endocrine consultation.
Selected tumor-marker trends after defined thyroid-cancer treatment.	Whether an asymptomatic person has thyroid cancer, or whether a new nodule is malignant.	Specialist-directed imaging, pathology, treatment history, and serial interpretation.
Whether another laboratory pattern, such as anemia, iron deficiency, dysglycemia, or a lipid abnormality, may overlap with thyroid-like symptoms.	A diagnosis involving another organ system or a reason to order every available biomarker.	Focused testing tied to the symptom pattern and the consequences of the result.

Symptoms, Risk Factors, and Patient Scenarios

The following framework helps organize testing questions. It does not show that a symptom is caused by the thyroid, and it is not a diagnostic algorithm.

Symptom, risk factor, or scenario	Possible significance	Targeted tests and other considerations
Fatigue, low energy, slowed thinking, or reduced concentration	May occur with thyroid dysfunction, anemia, low iron stores, vitamin B12 deficiency, sleep problems, mood disorders, infection, metabolic disorders, or medication effects.	Consider TSH and Free T4. When the history supports another cause, selected CBC, ferritin, iron and TIBC, vitamin B12, A1C, or glucose may add context.
Unexplained weight gain, weight-loss resistance, or cholesterol changes	May reflect thyroid dysfunction, metabolic risk, medications, menopause, sleep disruption, diet, genetics, or another condition.	Start with TSH and selected Free T4. Use lipid testing, ApoB, or metabolic testing only when it answers the broader risk question. See the Metabolic Health pillar.
Weight loss, tremor, heat intolerance, sweating, frequent bowel movements, or palpitations	May occur with hyperthyroidism, medication or stimulant effects, arrhythmia, anxiety, infection, thyroiditis, or another systemic illness.	Consider TSH, Free T4, and selected Total T3 or Free T3. Use TRAb or TSI if Graves' disease is suspected. A very rapid or irregular heartbeat, chest pain, fainting, severe shortness of breath, or confusion requires prompt care.
Cold intolerance, constipation, dry skin, hair changes, or slowed movement	May occur with hypothyroidism, anemia, iron deficiency, nutritional issues, medication effects, or other conditions.	Consider TSH and Free T4. Selected CBC, ferritin, iron and TIBC, and vitamin B12 may be appropriate when the history supports them.
Family or personal history of autoimmune thyroid disease or another autoimmune condition	Raises the pretest probability of autoimmune thyroid disease. Autoimmune conditions can cluster.	Consider TSH, Free T4, and selected TPO antibodies or thyroglobulin antibodies. Positive antibodies do not automatically mean treatment is needed.
Pregnancy, preconception planning, postpartum symptoms, or fertility concerns	Pregnancy-related physiology, thyroid dysfunction, postpartum thyroiditis, reproductive conditions, or another endocrine issue may affect the pattern.	Use TSH, Free T4, and selected antibodies with pregnancy-specific interpretation. When pregnancy status is uncertain and would change interpretation, the hCG Total Quantitative Test may add context. Coordinate abnormal results with an obstetric or endocrine professional.4
Previous thyroid surgery, radioactive iodine treatment, significant neck or chest radiation, pituitary disease, or thyroid-affecting medication exposure	The appropriate markers, interpretation, or monitoring target may differ. TSH may not answer the entire question in pituitary disease.	Use TSH and Free T4 with testing selected for the history. Specialist interpretation may be especially important. Do not use a general population reference interval as a personal treatment target.
Neck lump, swelling, pressure, hoarseness, or trouble swallowing	May reflect a thyroid nodule, goiter, inflammation, or another neck condition.	Thyroid-function testing can provide context, but examination and thyroid ultrasound may be needed. Progressive breathing or swallowing difficulty requires prompt evaluation.8

Thyroid Symptoms and Whole-Body Health Patterns

Thyroid hormones affect many organ systems, but common thyroid symptoms are not specific. Fatigue, weight change, lipid abnormalities, digestive symptoms, menstrual changes, hair loss, muscle complaints, and reduced exercise tolerance may reflect thyroid dysfunction, another condition, or more than one process at the same time. The goal is not to attach a large laboratory catalog to every symptom. The goal is to identify the smallest targeted test set that can distinguish the most plausible questions.

Clinical pattern	Targeted tests that may add context	Important limitation or next step
Persistent fatigue, weakness, hair changes, pallor, tingling, or cognitive symptoms	Selected Complete Blood Count with Differential and Platelets, Ferritin Test, Iron and Total Iron Binding Capacity Test, or Vitamin B12 Test. Consider Hemoglobin A1C or Glucose when metabolic symptoms or risk support that question.	These symptoms are nonspecific. Expanding the thyroid panel does not automatically identify the cause. Review sleep, bleeding, diet, medications, mood, infection, neurologic symptoms, and other risks.
Elevated LDL cholesterol, triglycerides, non-HDL cholesterol, or ApoB	Interpret TSH and selected Free T4 alongside an appropriate Lipid Panel and, when indicated, Apolipoprotein B.	Hypothyroidism can contribute to elevated cholesterol and triglycerides. Lipids may need reassessment after thyroid hormone levels normalize, but thyroid treatment does not replace a complete cardiovascular-risk evaluation.21
Persistent digestive symptoms, unexplained iron deficiency, nutrient deficiencies, or clustering of autoimmune conditions	When clinically appropriate, consider Tissue Transglutaminase IgA Antibody with Total IgA to support celiac-disease evaluation.	Autoimmune thyroid disease and celiac disease can occur together, but testing should be symptom- and risk-based. Celiac serology requires proper dietary and clinical context and does not establish every part of the diagnosis by itself.6, 22 See Digestive Health Lab Tests.
Menstrual irregularity, fertility concerns, or unexplained breast discharge	Use TSH and selected Free T4; add the hCG Total Quantitative Test when pregnancy status is relevant and the Prolactin Test when the history supports a prolactin question.	Age, cycle timing, pregnancy status, medications, sex, and the reproductive question affect test selection. Do not order every reproductive hormone automatically. See Women's Hormone Blood Tests and Fertility and Preconception Lab Tests.
Significant muscle pain, weakness, or exercise intolerance	When the history specifically supports a muscle, electrolyte, kidney, or liver question, selected Creatine Kinase, Total or Comprehensive Metabolic Panel may add context.	Recent strenuous exercise can elevate creatine kinase. These tests are not routine thyroid screening tests, and significant weakness may require prompt clinical examination rather than a larger outpatient panel.

Focused testing rule: Do not add cortisol, inflammatory markers, fasting insulin, broad reproductive hormone panels, iodine, selenium, creatine kinase, or other biomarkers to every thyroid evaluation. Each added test should answer a defined question and have a clear follow-up plan.

Thyroid Testing-Tier Overview

More testing is not automatically better. The most useful test set is the smallest one that can answer the current question while accounting for the consequences of false-positive, false-negative, incidental, or discordant findings.

Common or First-Line Tests

Test and quick facts	What it shows and how it is used	Preparation, influences, and limitations
TSH Test Use status: Common or first-line	Measures the pituitary signal to the thyroid. It is the preferred initial test for many questions about primary thyroid dysfunction.1, 2	Usually does not require fasting. Age, pregnancy, illness, medications, pituitary disease, time of collection, and assay interference can affect meaning.
Free T4 Test Use status: Common or first-line when TSH is abnormal or pituitary disease is possible	Measures unbound thyroxine and helps classify a high- or low-TSH pattern. It is also important in selected pregnancy, pituitary, and monitoring settings.	Medication timing, pregnancy, acute illness, binding abnormalities, biotin, and assay method may influence the result.
TSH Test with Reflex to Free T4 Use status: Focused first-line strategy	Measures TSH first and performs Free T4 only when the laboratory's reflex criterion is met. It can limit unnecessary testing while adding classification when TSH is abnormal.	Review the current product page for the reflex rule and possible additional charge. A reflex result still requires clinical interpretation and may not address pituitary-specific questions.

Risk-Based or Targeted Tests

Test and quick facts	What it shows and how it is used	Preparation, influences, and limitations
Total T4 Test Use status: Risk-based or targeted	Measures bound and unbound T4 together. It may add context when pregnancy or binding-protein changes make free-hormone interpretation more complex.	Estrogen exposure, pregnancy, liver or kidney conditions, illness, and binding-protein changes can alter total T4 without equivalent changes in thyroid function.
Total T3 Test Use status: Risk-based or targeted	May help evaluate a suppressed TSH or suspected hyperthyroidism, including patterns in which T3 is elevated more than T4.	Binding-protein changes affect total T3. It is usually not the preferred test for routine hypothyroid evaluation.
Free T3 Test Use status: Selected use	Measures unbound T3 and may add information in selected hyperthyroid questions or during specific therapy monitoring.	Free T3 methods can vary, and the test often adds little when evaluating suspected primary hypothyroidism.
Thyroid Peroxidase Antibodies Test Use status: Autoimmune evaluation	Detects antibodies to thyroid peroxidase and supports an autoimmune explanation, especially Hashimoto's disease.6	Antibodies can be positive when hormone levels are normal. The result does not measure current thyroid function or prove that symptoms come from the thyroid.
Thyroglobulin Antibodies Test Use status: Autoimmune or specialist-directed	Detects antibodies to thyroglobulin. It can add autoimmune context and is important when thyroglobulin is used for cancer monitoring.	It is not a thyroid-function test. Antibodies can make thyroglobulin results difficult to interpret.
Thyroid Peroxidase and Thyroglobulin Antibodies Test Use status: Combined autoimmune evaluation	Measures the two common antibody groups together when both are relevant to the question.	It does not replace TSH or thyroid-hormone testing and should not be repeated automatically when the result will not change care.
TRAb Test Use status: Graves' disease evaluation	Detects antibodies that bind the TSH receptor. It can help confirm Graves' disease, distinguish causes of thyrotoxicosis, assess relapse risk, or support selected pregnancy decisions.7	Assays and reported units vary. The result does not replace hormone measurements, examination, or pregnancy-specific professional care.
TSI Test Use status: Graves' disease evaluation	Detects thyroid-stimulating immunoglobulins that activate the TSH receptor. It may support diagnosis, monitoring, or relapse assessment in Graves' disease.	TSI and TRAb are related but are not interchangeable in every context. Interpret the specific method with thyroid-hormone results and clinical findings.

Monitoring and Specialist-Directed Tests

Test and quick facts	What it shows and how it is used	Preparation, influences, and limitations
TSH Test with selected Free T4 Test Use status: Monitoring	Tracks response after a treatment change or during ongoing management. The appropriate marker depends on the condition, therapy, pregnancy status, and pituitary function.	TSH may lag behind a recent physiologic or treatment change. Consistent collection timing and professional interpretation are important.13, 15
Thyroglobulin Panel Test Use status: Specialist-directed cancer monitoring	Measures thyroglobulin with thyroglobulin antibodies for follow-up after defined treatment for differentiated thyroid cancer.11	Not a screening test. Interpretation depends on remaining thyroid tissue, antibodies, assay method, treatment history, imaging, and trend.
Calcitonin Test Use status: Specialist-directed	Used in selected evaluation or follow-up for medullary thyroid cancer and some familial-risk settings.12	Not part of routine thyroid panels. Results may be influenced by factors other than cancer and require specialist context.
TSI and TBII Panel Use status: Specialist-directed antibody panel	Combines two TSH-receptor antibody measurements for selected Graves' disease questions.	Verify why both measurements are needed before ordering. A larger panel is not automatically more informative.

Emerging, Insufficiently Validated, or Generally Not Appropriate for Broad Routine Screening

• Reverse T3 Test: Reverse T3 can change during severe illness and altered metabolism, but it is generally not used to assess routine hypothyroidism or hyperthyroidism. Ordering should be tied to a defined specialist question, not vague symptoms alone.¹⁷
• Broad thyroid panels without a defined question: Adding many markers increases cost and the chance of incidental or discordant findings without necessarily improving care.
• Thyroglobulin Panel Test and Calcitonin Test: These are not broad cancer-screening tests for people without a defined indication.^{10, 11}
• Repeated antibody testing without a management question: Antibody concentrations do not directly measure current thyroid function, and repeated testing may not change decisions.
• Population screening in asymptomatic, nonpregnant adults: The balance of benefits and harms remains uncertain according to the U.S. Preventive Services Task Force; individualized risk and professional guidance matter.⁹

TSH-Led Thyroid-Test Selection Framework

Educational framework, not a diagnostic or treatment algorithm: Test selection should begin with the question being asked, not with the largest available panel.

1. Define the purpose. Is the goal risk-based screening, symptom evaluation, confirmation of a suspected cause, baseline testing, medication monitoring, pregnancy-related assessment, or specialist-directed cancer follow-up?
2. For many primary thyroid-function questions, start with the TSH Test. A TSH Test with Reflex to Free T4 can be a focused option when its reflex rule matches the intended question.
3. Add the Free T4 Test when needed. It helps classify an abnormal TSH pattern and is important when pituitary disease, pregnancy, acute illness, or monitoring makes TSH alone insufficient.
4. Use T3 selectively. A Total T3 Test or Free T3 Test may help with selected low-TSH or hyperthyroid questions. It is not automatically needed for suspected hypothyroidism.
5. Add antibodies only when the cause matters. The Thyroid Peroxidase Antibodies Test and Thyroglobulin Antibodies Test address Hashimoto-related autoimmunity. The TRAb Test and TSI Test address Graves-related autoimmunity.
6. Use monitoring markers only for the condition they were designed to follow. The Thyroglobulin Panel Test and Calcitonin Test require defined specialist indications.
7. Check for reasons a result may be misleading. Review pregnancy, acute illness, pituitary disease, medication and supplement use, timing, assay method, and prior results before interpreting an unexpected pattern.
8. Plan what happens after the result. Before testing, know whether an abnormal or discordant finding would lead to repetition, another method, imaging, specialist evaluation, or urgent care.

Hypothyroid-Pattern Versus Hyperthyroid-Pattern Results

The combinations below are simplified educational patterns. They are not diagnoses, universal rules, treatment instructions, or substitutes for the laboratory's units and reference interval.

General laboratory pattern	Possible interpretation	Follow-up questions and limitations
High TSH with low Free T4	Can support a primary hypothyroid pattern.	Review symptoms, medication use, autoimmune cause, pregnancy, repeat confirmation, treatment history, and possible assay interference. Unusual pituitary or thyroid-hormone-resistance patterns require specialist context when results do not fit.
High TSH with laboratory-normal Free T4	May fit a subclinical hypothyroid pattern.	Consider degree and persistence, age, pregnancy, symptoms, antibodies, medications, and cardiovascular context. A single mild abnormality may be temporary, and the edge of a reference interval is not automatically a treatment threshold.
Low TSH with high Free T4 or Total T3	Can support a primary hyperthyroid pattern.	Consider Graves' disease, thyroiditis, autonomous nodules, medication or supplement exposure, and the need for antibody testing or imaging. Biotin and other assay interferences can mimic this pattern. Severe symptoms may require urgent care.
Low TSH with laboratory-normal thyroid-hormone results	May fit a subclinical hyperthyroid pattern.	Consider persistence, medications, age, heart rhythm, bone risk, pregnancy, acute illness, and other causes of TSH suppression. Repeat or targeted testing may be needed.
Low or inappropriately normal TSH with low Free T4	May raise concern for pituitary or hypothalamic disease, severe illness, or medication effects.	TSH is not a reliable stand-alone measure when the hypothalamic-pituitary axis is impaired. Other pituitary hormones, imaging, and specialist review may be required.1
Results that do not agree with one another or with the patient's condition	May reflect timing, assay interference, binding-protein effects, medications, illness, or a less common disorder.	Consider repeat collection, another assay method, dilution or interference studies, and laboratory or endocrine consultation. Do not force discordant values into a common diagnosis without investigating the mismatch.16

Pregnancy and Postpartum Thyroid-Testing Considerations

Pregnancy changes thyroid physiology, binding proteins, and the interpretation of TSH and thyroid-hormone results. Human chorionic gonadotropin can stimulate the TSH receptor, especially early in pregnancy, so pregnancy status matters when interpreting a low TSH result. Trimester-, population-, and method-appropriate intervals are preferred when available.^{1, 4}

• If pregnancy status is uncertain and the result would change interpretation or next steps, the hCG Total Quantitative Test may provide relevant context.
• The TSH Test and Free T4 Test must be interpreted with pregnancy-specific context; a nonpregnant adult reference interval may be inappropriate.
• The TRAb Test or TSI Test may be used in selected patients with current or prior Graves' disease because maternal antibodies can cross the placenta. This is specialist-directed care.
• Do not start, stop, or change thyroid medication based on a self-interpreted result. Preconception, pregnancy, and postpartum thyroid management should involve an obstetric and/or endocrine professional.

What Is Postpartum Thyroiditis?

Postpartum thyroiditis can cause a temporary thyrotoxic phase, a hypothyroid phase, or both. The classic sequence is thyrotoxicosis followed by hypothyroidism, but some patients experience only one phase. Symptoms can be mistaken for normal postpartum changes. Most affected women regain normal thyroid function within 12 to 18 months after symptoms begin, but approximately 20% of those who enter the hypothyroid phase remain hypothyroid. Testing and treatment depend on the phase, symptoms, pregnancy plans, and individual history.²⁰

Individual Thyroid Tests Versus Panels

Test or panel and use status	When it may be useful	Advantages, limitations, and question to ask
TSH Test Use status: Common or first-line	Initial assessment for many primary thyroid-function questions.	Focused and widely used, but insufficient when pituitary disease, pregnancy, acute illness, medication effects, or discordant symptoms make TSH unreliable. Ask: Would an abnormal or unexpected result lead to Free T4 measurement?
TSH Test with Reflex to Free T4 Use status: Focused first-line strategy	When TSH should be measured first and Free T4 is needed only if the laboratory's reflex criterion is met.	May reduce unnecessary Free T4 testing, but reflex rules and possible additional charges must be reviewed. Ask: Exactly what TSH result triggers the reflex?
TSH and Free T4 Test Use status: Focused combined testing	When both values are needed regardless of the first result, including selected pituitary, pregnancy, monitoring, or discordant-symptom settings.	Provides the central signaling-and-hormone pair, but it does not identify an autoimmune cause or answer every hyperthyroid question. Ask: Will both values change interpretation or follow-up?
Free T3, Free T4, and TSH Panel Use status: Selected panel	Selected questions in which all three measurements are expected to add information.	Collects three measurements together, but Free T3 is not routinely necessary for every hypothyroid question. Ask: What defined question will Free T3 answer?
Thyroid Peroxidase and Thyroglobulin Antibodies Test Use status: Targeted autoimmune panel	When autoimmune thyroid disease is suspected and both common antibody groups are relevant.	Combines two autoimmune markers but does not measure current thyroid function and may be positive when hormone levels are normal. Ask: Will the antibody result change counseling or monitoring?
TSI and TBII Panel Use status: Specialist-directed	Selected Graves' disease questions in which two related receptor-antibody measurements are needed.	Often more testing than a routine thyroid-function question requires. Ask: Why are both receptor-antibody measurements needed?

Thyroid Test-Name and Alias Crosswalk

Linked test	Common aliases	Key distinction
TSH Test	Thyroid-stimulating hormone, thyrotropin	A pituitary signal, not a hormone made by the thyroid.
Free T4 Test	Free thyroxine, FT4	Measures unbound T4; it is not the same as total T4.
Total T4 Test	Total thyroxine, TT4	Includes bound and unbound T4 and is affected by binding proteins.
Total T3 Test	Total triiodothyronine, TT3	Includes bound and unbound T3.
Free T3 Test	Free triiodothyronine, FT3	Measures unbound T3; assay performance and clinical utility differ from total T3.
Thyroid Peroxidase Antibodies Test	TPO antibodies, TPOAb, anti-TPO	Supports autoimmune-thyroid evaluation; it is not a hormone test.
Thyroglobulin Antibodies Test	TgAb, anti-thyroglobulin antibodies	May indicate autoimmunity and can interfere with thyroglobulin measurement.
TRAb Test	TSH-receptor antibody, TSH receptor-binding antibody	A broad receptor-antibody measurement used in Graves-related evaluation.
TSI Test	Thyroid-stimulating immunoglobulin	Focuses on antibodies that stimulate the TSH receptor.
Reverse T3 Test	rT3, reverse triiodothyronine	Measures an inactive metabolite and is not a routine thyroid-function test.

Biotin, Medication, Illness, and Preparation Matrix

Preparation varies by product and by the other tests collected at the same visit. Review the current product instructions. Do not stop or change a prescription medication or supplement solely to prepare for testing unless the prescribing or ordering professional directs you to do so.

Factor	Possible effect on testing	Preparation guidance and caution
Biotin supplements	Depending on the assay, biotin can affect TSH, Free T4, Total T3, Free T3, antibodies, and thyroglobulin. It can produce falsely high or falsely low values; one possible pattern is falsely low TSH with falsely high T4 or T3.	Tell the ordering professional and laboratory the product, dose, and time last taken. Follow the exact test and professional instructions. Do not apply one universal pause interval to every dose and assay.1, 5
Thyroid-hormone medication	Collection soon after a dose can change measured hormone concentrations; TSH may respond more slowly than circulating hormone levels.	Use consistent collection timing and follow the prescriber's instructions. Never skip, stop, or change medication solely to prepare for testing unless directed.13, 15
T3-containing therapy	T3 concentrations can rise and fall over hours, so a single Total T3 or Free T3 result is timing-dependent.	Record the exact product, dose, and time of the last dose. Interpretation is often specialist-directed.
Estrogen exposure, pregnancy, or binding-protein changes	Can alter total T4 and total T3, and pregnancy changes hCG, binding proteins, physiology, and reference intervals.	Record pregnancy status, estrogen-containing medication, and other relevant conditions. Use method- and pregnancy-stage-appropriate interpretation.
Acute or severe illness	Illness can temporarily change TSH, T4, T3, binding proteins, and thyroid-hormone metabolism, producing a nonthyroidal illness pattern.	Tell the ordering professional about recent illness and why testing is being performed. Routine outpatient interpretation may be misleading during acute illness.
Iodine exposure, contrast, amiodarone, lithium, or other thyroid-affecting medications	Can alter thyroid physiology or the expected test pattern.	Provide a complete medication, supplement, procedure, and exposure history. Do not stop a medication without guidance.
Pituitary or hypothalamic disease	TSH can be low, normal, or only mildly abnormal despite inadequate thyroid-hormone signaling.	Do not interpret TSH alone. Free T4, other pituitary tests, imaging, and specialist review may be needed.
Assay method, heterophile antibodies, thyroid-hormone autoantibodies, or other analytical interference	Can create values that are internally inconsistent or do not fit the patient's symptoms, examination, or prior results.	Discuss unexplained discordant results with the laboratory or an endocrine professional. Repeat testing with another method or interference studies may be appropriate before major decisions.1, 16

How to Understand Your Thyroid Results

Interpret thyroid results as a pattern, not as isolated numbers. Start with the exact test name, value, unit, laboratory reference interval, collection conditions, and prior results. Then ask whether the measurements agree with one another and with symptoms, medications, supplements, pregnancy status, and health history.

A laboratory flag only shows that a result falls outside that laboratory's reference interval. It does not automatically establish a diagnosis, determine severity, or show that treatment is needed. A value inside the interval also does not guarantee that every thyroid-related question has been answered. For a broader explanation, see How to Read and Understand Your Lab Results.

Reference Interval, Decision Threshold, Target, and Trend

Term	What it means and how it is used	Why caution is needed
Laboratory reference interval	A range expected for a defined reference population using a specific method. It helps flag results for review.	Intervals may differ by population, age, pregnancy, geography, assay platform, and laboratory method. Outside the interval does not automatically equal disease; inside does not guarantee health.
Diagnostic or decision threshold	A value or pattern used with clinical evidence to support diagnosis, further testing, referral, or a treatment discussion.	It may differ by condition, age, pregnancy, comorbidity, and guideline. It is not necessarily the same as the edge of the laboratory interval.
Treatment or monitoring target	A goal selected for a person already receiving care based on the diagnosis and treatment plan.	Targets can differ with pregnancy, thyroid-cancer history, age, pituitary disease, medication, and risk. Do not apply another person's target or change medication without the prescriber.
Trend	Change across comparable measurements over time. It can help distinguish persistent change from short-term variation.	Timing, illness, medication, laboratory method, and biological variation affect trends. A small numerical change may not be clinically meaningful.

Fictional Thyroid-Panel Walkthrough

Educational example, not a diagnosis: The details below are qualitative placeholders. Use the actual laboratory's units and intervals when reviewing a real report.

Fictional report detail	What to consider	Possible follow-up question
TSH is flagged above this laboratory's interval.	Magnitude, prior values, pregnancy, illness, medications, supplement use, and possible assay interference.	Is the finding persistent, and does Free T4 classify the pattern?
Free T4 is within this laboratory's interval.	Method, timing, symptoms, and whether the combination may fit a subclinical pattern.	Should the pair be repeated under comparable conditions before drawing a conclusion?
TPO antibodies are positive.	The finding supports autoimmune context but does not measure current hormone function.	Would the antibody result change monitoring, pregnancy planning, or counseling?
Biotin use was not recorded, and there is no comparable prior measurement.	Possible interference and the absence of a trend reduce confidence in a one-time interpretation.	Should supplement use and collection conditions be clarified before repetition?

Reverse T3, Broad Panels, and Clinical Utility

The Reverse T3 Test measures an inactive T3 metabolite. Reverse T3 can change during severe illness, calorie restriction, and altered metabolism, but it has limited routine clinical utility for evaluating hypothyroidism or hyperthyroidism. It should not be used alone to diagnose a thyroid disorder, explain vague symptoms, determine whether the body is "using" thyroid hormone, or direct treatment.¹⁷

A broad panel is less likely to add value when:

• there is no defined clinical question;
• the same information is already available from recent, comparable results;
• the person is acutely ill and the question can safely wait until recovery;
• the added markers are unlikely to change follow-up;
• the test requires specialist interpretation that is not available;
• the central question concerns a thyroid nodule's structure, which is addressed with examination and imaging rather than a larger blood panel; or
• urgent symptoms require immediate evaluation instead of routine outpatient testing.

Over-testing can lead to incidental abnormalities, false-positive or false-negative findings, anxiety, unnecessary repetition, and referrals that do not improve the answer to the original question.

When Repeat or Confirmatory Testing May Be Needed

Repeat or confirmatory testing may be appropriate when:

• a result is unexpected or does not fit the symptoms and examination;
• a mild abnormality may reflect temporary illness, pregnancy-related physiology, medication effects, or assay interference;
• biotin or another interfering substance may have affected the sample;
• the TSH Test is abnormal and a Free T4 Test is needed to classify the pattern;
• a low TSH result requires selected Total T3 or Free T3 measurement;
• the suspected cause requires a Thyroid Peroxidase Antibodies Test, TRAb Test, or TSI Test;
• the laboratory or clinician recommends another assay method to investigate discordant results; or
• monitoring is needed after a treatment change, with timing selected by the treating professional.

Repeat testing should answer a specific question. Repeating too soon may capture normal biological or analytical variation rather than meaningful change, and TSH may take time to reflect a recent physiologic or treatment change.^{1, 13}

When Professional or Urgent Care Is Needed

Arrange timely professional review for persistent symptoms, a new neck mass, pregnancy-related thyroid concerns, clearly abnormal or discordant results, suspected pituitary disease, or questions about thyroid medication. Examination, imaging, electrocardiography, or specialist evaluation may be more important than additional blood tests.

Seek prompt or emergency evaluation for severe chest pain, fainting, severe shortness of breath, sudden confusion, marked weakness, a very rapid or irregular heartbeat, severe dehydration, rapidly worsening swelling or difficulty breathing or swallowing, or concerning symptoms during pregnancy. Routine direct-access testing is not an emergency service.

Explore Related Thyroid Guides and Pillars

Related Thyroid Guides

• Thyroid-Stimulating Hormone: Impact of High and Low TSH Levels explains why TSH may be high or low and why the pattern requires context.
• Graves' Disease: Symptoms, Causes, and Treatments focuses on autoimmune hyperthyroidism and receptor-antibody testing.
• Thyroid Nodules Explained: A Complete Guide clarifies why ultrasound and sometimes biopsy, rather than blood tests alone, evaluate a nodule.
• Thyroid Cancer Symptoms and the Limits of Blood Testing explains when tumor-related tests may and may not help.
• The Connection Between Thyroid Function and Weight Gain separates thyroid-related weight effects from other metabolic influences.
• The Connection Between Thyroid Function and Hair Loss reviews thyroid and nonthyroid causes of hair changes.
• Common Thyroid Problems in Women covers life-stage, reproductive, pregnancy, and postpartum context.
• Nutrient Deficiencies Linked to Thyroid Disorders reviews selected nutrient patterns that may overlap with thyroid symptoms.

Related Pillar Articles

• Metabolic Health, Weight Loss, and GLP-1 Monitoring
• Women's Hormone Blood Tests
• Men's Health Blood Tests
• Fertility and Preconception Lab Tests
• Vitamin and Nutrient Deficiency Tests
• CBC and Anemia Blood Tests
• Digestive Health Lab Tests
• Inflammation and Autoimmune Blood Tests

Related Individual Thyroid Tests and Panels

Common Starting Options

• TSH Test: A common first-line measure of pituitary signaling to the thyroid.
• Free T4 Test: Measures unbound thyroxine and helps interpret an abnormal TSH pattern.
• TSH Test with Reflex to Free T4: Starts with TSH and adds Free T4 when the current product's reflex criterion is met.
• TSH and Free T4 Test: Measures both central values together when both are needed regardless of the first result.

Targeted T4 and T3 Options

• Total T4 Test: Selected assessment of bound and unbound thyroxine together.
• Total T3 Test: Selected evaluation of low-TSH or hyperthyroid patterns.
• Free T3 Test: Selected measurement of unbound triiodothyronine.
• Reverse T3 Test: Nonroutine measurement that should be ordered only for a defined specialist question.

Autoimmune Thyroid and Graves' Disease Options

• Thyroid Peroxidase Antibodies Test: Supports Hashimoto-related autoimmune evaluation.
• Thyroglobulin Antibodies Test: Adds autoimmune context and helps interpret thyroglobulin.
• Thyroid Peroxidase and Thyroglobulin Antibodies Test: Combines the two common antibody groups.
• TRAb Test: TSH-receptor binding antibody assessment for selected Graves-related questions.
• TSI Test: Measures stimulating TSH-receptor antibodies.
• TSI and TBII Panel: Specialist-directed combination of two receptor-antibody measurements.

Specialist-Directed Monitoring Options

• Thyroglobulin Panel Test: Used for follow-up after defined treatment for differentiated thyroid cancer.
• Calcitonin Test: Used for selected evaluation or monitoring related to medullary thyroid cancer or familial risk.

Focused Thyroid Panel

• Free T3, Free T4, and TSH Panel: Combines three thyroid-function measurements when each has a defined purpose.

Selected Tests for Symptoms That May Overlap With Thyroid Disease

When the history supports another explanation for fatigue, weakness, hair changes, cognitive symptoms, metabolic abnormalities, digestive symptoms, or reproductive concerns, targeted nonthyroid testing may be more useful than expanding the thyroid panel.

• Complete Blood Count with Differential and Platelets: Evaluates blood-cell patterns, including anemia and infection-related clues.
• Ferritin Test: Evaluates stored iron; ferritin can also rise with inflammation.
• Iron and Total Iron Binding Capacity Test: Provides iron availability and binding information when clinically relevant.
• Vitamin B12 Test: Evaluates a nutrient deficiency that can overlap with fatigue, anemia, and neurologic symptoms.
• Hemoglobin A1C and Glucose: Provide selected metabolic context when symptoms or risk factors support dysglycemia evaluation.
• Lipid Panel and Apolipoprotein B: Support cardiovascular-risk assessment when dyslipidemia overlaps with a thyroid question.
• Tissue Transglutaminase IgA Antibody with Total IgA: Supports selected celiac-disease evaluation when symptoms, iron deficiency, nutrient deficiencies, or autoimmune clustering make the question relevant.
• hCG Total Quantitative Test: Provides pregnancy context when pregnancy status is uncertain and would change thyroid-result interpretation.
• Prolactin Test: May add information for selected menstrual, fertility, or breast-discharge questions.
• Creatine Kinase, Total and Comprehensive Metabolic Panel: May add context for selected muscle, electrolyte, liver, or kidney questions.
• Iodine, Serum/Plasma or Selenium: Not routine thyroid tests; consider only when a specific nutritional, exposure, malabsorption, or specialist-directed question supports testing.

How Ulta Lab Tests May Help

Eligible patients can review available thyroid tests and panels online, read the current product description and preparation instructions, complete the ordering and collection process, and use the results to support a more informed conversation with a qualified healthcare professional. Availability and requirements can vary. Review how direct-access lab testing works and what to expect before ordering.

Choose testing for a defined question. A larger panel is not automatically more useful, and direct-access testing does not replace examination, imaging, emergency care, or clinician-directed medication management.

Questions to Ask a Healthcare Professional

1. Does my history make thyroid dysfunction likely enough to test?
2. Is the TSH Test an appropriate starting point, or do I need the Free T4 Test at the same time?
3. What defined question would a T3 measurement answer?
4. Would thyroid antibodies change the evaluation, monitoring plan, or pregnancy counseling?
5. Could pregnancy, recent illness, pituitary disease, or another health condition change interpretation?
6. Could any medication, supplement, procedure, or recent dose timing affect the results?
7. Should I use the same laboratory and comparable collection timing for follow-up?
8. If the results are discordant, should the sample be repeated or tested by another method?
9. Would examination, ultrasound, electrocardiography, or another test answer the question better?
10. Which symptoms should prompt urgent care rather than routine testing?

Frequently Asked Questions About Thyroid Blood Tests

What is usually the first thyroid blood test?

The TSH Test is the preferred initial test for many questions about primary thyroid dysfunction because TSH responds sensitively to changes in circulating thyroid hormone. It is not sufficient in every setting, including suspected pituitary disease, pregnancy, acute illness, or some medication contexts.^{1, 2}

Is TSH alone enough?

Sometimes, but not always. The Free T4 Test helps classify an abnormal TSH pattern and can be essential when TSH may be unreliable. A TSH Test with Reflex to Free T4 may be a focused option when its reflex criteria match the question.

Do I need Free T3 with every thyroid panel?

No. The Free T3 Test can help with selected hyperthyroid or treatment-monitoring questions, but it often adds little to routine evaluation for primary hypothyroidism. The test should have a defined purpose.

What does a positive TPO antibody result mean if TSH is normal?

A positive Thyroid Peroxidase Antibodies Test supports autoimmune thyroid activity, but it does not show that thyroid hormone levels are currently abnormal or that every symptom is thyroid-related. Follow-up depends on the clinical setting, pregnancy considerations, symptoms, and future thyroid-function results.

What is the difference between TRAb and TSI?

The TRAb Test broadly detects antibodies that bind the TSH receptor, while the TSI Test focuses on antibodies with stimulating activity. They address related Graves' disease questions, but methods and clinical uses are not identical.

Does a high TSH result diagnose hypothyroidism?

Not by itself. A high TSH Test result should be interpreted with the Free T4 Test, symptoms, pregnancy status, medications, illness, assay limitations, and sometimes repeat testing.

Does a low TSH result always mean Graves' disease?

No. A low TSH Test result can occur with Graves' disease, thyroiditis, autonomous nodules, medication or supplement effects, pregnancy-related physiology, pituitary conditions, acute illness, or assay interference. Hormone measurements and sometimes the TRAb Test or TSI Test help clarify the pattern.

Can biotin affect thyroid results?

Yes. Biotin can interfere with some immunoassays and may create falsely high or falsely low results. Tell the ordering professional and laboratory the dose and time last taken, and follow the current product and professional instructions. Do not apply one universal pause interval to every dose and assay.^{1, 5}

Do thyroid blood tests require fasting?

Many thyroid tests do not require fasting, but preparation depends on the exact product and any other tests collected at the same time. Review the current product instructions and use consistent timing for follow-up when practical.

How should thyroid testing be interpreted during pregnancy?

Pregnancy changes hCG, binding proteins, TSH, and thyroid-hormone interpretation. Pregnancy-, population-, trimester-, and method-appropriate intervals are preferred when available. Abnormal results should be reviewed promptly with an obstetric or endocrine professional.⁴

What is postpartum thyroiditis?

Postpartum thyroiditis can cause a thyrotoxic phase, a hypothyroid phase, or both. Symptoms may be confused with normal postpartum changes. Most affected women regain normal thyroid function within 12 to 18 months after symptoms begin, but approximately 20% of those who enter the hypothyroid phase remain hypothyroid. Testing and follow-up should be coordinated with an obstetric or endocrine professional.²⁰

Can blood tests tell whether a thyroid nodule is cancerous?

No. Thyroid-function results can be normal even when a nodule is present. Examination and ultrasound evaluate structure, and fine-needle aspiration may be needed based on the nodule's features and size.⁸

Is thyroglobulin a thyroid-cancer screening test?

No. The Thyroglobulin Panel Test is primarily used for specialist-directed follow-up after defined treatment for differentiated thyroid cancer. It is not a general test for finding a new thyroid cancer.¹¹

Is calcitonin part of a routine thyroid panel?

No. The Calcitonin Test is used for selected questions involving medullary thyroid cancer or familial risk and is not routine thyroid-function testing.¹²

Is reverse T3 useful?

The Reverse T3 Test has limited routine clinical utility for hypothyroidism or hyperthyroidism. It may be considered only for a defined specialist question and should not be used alone to direct treatment.¹⁷

Can hypothyroidism affect cholesterol?

Yes. Hypothyroidism can contribute to elevated cholesterol and triglycerides. When thyroid dysfunction is identified, a Lipid Panel may need to be reassessed after thyroid hormone levels return to an appropriate range. Thyroid treatment does not replace complete cardiovascular-risk assessment or appropriate lipid management.^{18, 21}

Can celiac disease and autoimmune thyroid disease occur together?

Yes. Celiac disease and autoimmune thyroid disorders such as Hashimoto's disease or Graves' disease can occur together. Selected Tissue Transglutaminase IgA Antibody with Total IgA may be reasonable when thyroid autoimmunity occurs with persistent digestive symptoms, iron deficiency, anemia, nutrient deficiencies, unexplained weight loss, or relevant family or autoimmune history. Testing is not automatically necessary for every person with a thyroid condition.^{6, 22}

Should everyone with thyroid symptoms take iodine or selenium?

No. Iodine and selenium are necessary nutrients, but more is not necessarily better. Excess iodine can cause thyroid dysfunction in susceptible people, and selenium deficiency is uncommon in the United States while excessive intake can cause adverse effects. Supplements should be based on a defined nutritional or clinical question rather than vague symptoms alone. The Iodine, Serum/Plasma Test and Selenium Test are not routine thyroid-function tests.^{23, 24}

When should an abnormal thyroid result be repeated?

Timing depends on the pattern, severity, symptoms, pregnancy, medication changes, and suspected interference. Unexpected or mild abnormalities may need confirmation, while severe symptoms or markedly abnormal patterns may require immediate professional evaluation rather than routine repetition.

Main Takeaways About Thyroid Blood Tests

• The TSH Test is a common starting point for primary thyroid-function questions.
• The Free T4 Test helps classify an abnormal TSH pattern, while T3 testing is most useful for selected low-TSH or hyperthyroid questions.
• Thyroid antibodies help identify autoimmune causes; they do not measure current thyroid function by themselves.
• Functional, autoimmune, and structural thyroid questions require different testing strategies.
• Thyroid-like symptoms can overlap with anemia, iron or B12 deficiency, dysglycemia, lipid abnormalities, celiac disease, reproductive conditions, medication effects, sleep problems, and other causes.
• Pregnancy, postpartum physiology, illness, medications, supplements, timing, and assay method can materially affect interpretation.
• Blood tests cannot determine whether a thyroid nodule is benign or malignant.
• A focused test set tied to a clear question is usually more useful than an indiscriminate broad panel.

Review the exact product instructions before testing, interpret results as a pattern and trend, and use abnormal or discordant findings to support a conversation with a qualified healthcare professional. For the testing process, see the Direct-Access Lab Testing guide. For result interpretation, use How to Read and Understand Your Lab Results.

Primary References

1. Thyroid-Stimulating Hormone and Thyroid Hormones: Triiodothyronine and Thyroxine, an American Thyroid Association-Commissioned Review of Current Clinical and Laboratory Status. American Thyroid Association.
2. Thyroid Function Tests. American Thyroid Association.
3. Thyroid Tests. National Institute of Diabetes and Digestive and Kidney Diseases.
4. American Thyroid Association 2026 Guidelines for Thyroid Disease in Preconception, Pregnancy, and Postpartum. Thyroid; 2026.
5. Testing for Biotin Interference in In Vitro Diagnostic Devices. U.S. Food and Drug Administration.
6. Hashimoto's Disease. National Institute of Diabetes and Digestive and Kidney Diseases.
7. Graves' Disease. National Institute of Diabetes and Digestive and Kidney Diseases.
8. Thyroid Nodules. American Thyroid Association.
9. Thyroid Dysfunction: Screening. U.S. Preventive Services Task Force.
10. Thyroid Cancer: Screening. U.S. Preventive Services Task Force.
11. 2025 American Thyroid Association Management Guidelines for Adult Patients With Differentiated Thyroid Cancer. Thyroid; 2025.
12. Calcitonin Test. MedlinePlus.
13. Thyroid Hormone Treatment. American Thyroid Association.
14. Hashimoto's Disease: Planning and Treatment. American Association of Clinical Endocrinology.
15. Thyroid Hormone Levels Affected by Time of Blood Sampling in Thyroxine-Treated Patients. PubMed.
16. Approach to the Patient With Raised Thyroid Hormones and Nonsuppressed TSH. The Journal of Clinical Endocrinology & Metabolism; 2024.
17. Reverse T3 Testing and Clinical Utility. American Thyroid Association, Clinical Thyroidology for the Public.
18. Hypothyroidism (Underactive Thyroid). National Institute of Diabetes and Digestive and Kidney Diseases.
19. Hyperthyroidism (Overactive Thyroid). National Institute of Diabetes and Digestive and Kidney Diseases.
20. Postpartum Thyroiditis. American Thyroid Association.
21. Lipid Management Guideline. Endocrine Society.
22. Definition and Facts for Celiac Disease. National Institute of Diabetes and Digestive and Kidney Diseases.
23. Iodine: Fact Sheet for Health Professionals. National Institutes of Health Office of Dietary Supplements.
24. Selenium: Fact Sheet for Health Professionals. National Institutes of Health Office of Dietary Supplements.

Editorial Disclosure, Authorship, and Medical Note

Ulta Lab Tests provides direct-access laboratory testing. Product links are included when they match the educational topic. Purchasing a test is not a substitute for diagnosis, treatment, imaging, specialist care, or urgent medical evaluation.

Written by: John R.
Originally published: August 1, 2026
Last updated: August 11, 2026

Medical note: This guide is educational. A qualified healthcare professional should select and interpret testing in the context of symptoms, diagnoses, medications, supplements, pregnancy status, nutrition, hydration, examination findings, and prior results. Do not start, stop, or change a prescription medication based on this article or one laboratory result.