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The Complete Guide to Lab Tests and Blood Work

Understand what lab tests measure, why blood tests are ordered, and how blood work supports screening, diagnostic evaluation, and monitoring.
August 1, 2026
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Understand what lab tests measure, why blood tests are ordered, and how blood work supports screening, diagnostic evaluation, and monitoring.

Laboratory tests analyze blood, urine, stool, saliva, swabs, tissue, breath, or other specimens to measure substances, cells, antibodies, organisms, genetic material, and other biological characteristics. They may support screening, risk assessment, diagnostic evaluation, baseline measurement, medication monitoring, disease monitoring, or confirmation of an earlier finding. Common blood work includes a complete blood count, metabolic panels, glucose and A1C, lipid testing, thyroid tests, iron studies, and selected vitamin or inflammation markers. The right test depends on the health question. A laboratory result is one part of an evaluation and usually must be interpreted with symptoms, history, medications, examination findings, trends, and—when needed—imaging or other procedures. [1] [2]

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Key Facts About Lab Tests

  • A test usually measures one analyte or one defined process; a panel groups related tests.
  • Blood is common, but laboratory testing may also use urine, stool, saliva, swabs, breath, tissue, cells, or other body fluids.
  • Tests may be used for screening, risk assessment, diagnostic support, baseline measurement, confirmation, or monitoring. These purposes are not interchangeable.
  • A laboratory reference interval is not automatically a diagnostic cutoff, treatment target, or personal goal. Methods and intervals may differ between laboratories. [1]
  • A normal result does not guarantee health, and an abnormal result does not automatically confirm disease.
  • More testing is not always better. Unfocused testing can create incidental findings, false-positive results, anxiety, cost, and unnecessary follow-up. [16]
  • Fasting is required for some tests, not all. Timing, hydration, exercise, acute illness, alcohol, smoking, medications, vitamins, and supplements can affect results. [2] [3] [15]
  • Severe, sudden, rapidly worsening, or potentially life-threatening symptoms require prompt medical attention, not routine wellness testing.
Wide lab testing preview with blood collection tubes, a urine specimen, and a dashboard for CBC, CMP, lipids, thyroid, kidney, liver, and nutrients.
Blood and urine specimens with a digital overview of common lab tests, blood work, health markers, and laboratory panels.

What Are Lab Tests and Blood Work?

A laboratory test is a procedure that examines a specimen to answer a specific biological question. The result may be a number, a positive or negative finding, a detected organism or genetic sequence, a visual description, or a professional interpretation. Laboratory testing is most useful when the question is clearly defined before the sample is collected.

Biomarker
A measurable biological characteristic. Examples include glucose concentration, hemoglobin level, an antibody, a DNA variant, or the presence of a microorganism. A biomarker may provide useful information without being specific to a single disease.

Blood work
A general term for one or more tests performed on whole blood, serum, or plasma. Blood work may include cell counts, blood chemistry measurements, hormones, antibodies, nutritional markers, or molecular tests.

Individual test
A test focused on one analyte or a narrowly defined measurement, such as TSH, ferritin, or vitamin B12.

Panel
A group of related tests performed and reported together, such as a complete blood count (CBC), basic metabolic panel (BMP), comprehensive metabolic panel (CMP), or lipid panel. A panel may be standardized by a laboratory or assembled for a specific purpose.

Profile
A term often used interchangeably with “panel,” although the included tests may vary. Always review the exact components rather than relying only on the profile name.

Screening test
A test used in people without a known diagnosis—and sometimes without symptoms—to look for a condition or risk that may benefit from earlier evaluation. Screening decisions should consider age, risk factors, available evidence, and recommended testing intervals.

Diagnostic-support test
A test used with symptoms, medical history, physical examination findings, and diagnostic criteria to help explain a health concern. Laboratory testing commonly supports a diagnosis, but it does not replace the rest of the clinical evaluation.

Monitoring test
A measurement repeated over time to follow a condition, assess treatment response, evaluate a medication’s effects, or identify a potential safety concern.

Confirmatory test
A repeated test or a different type of test used to verify an unexpected, borderline, screening, or preliminary result before a major conclusion or treatment decision is made.

What Specimens Can Laboratory Tests Use?

Comparison of blood, urine, stool, saliva, swab, and specialized laboratory specimens with common uses, test examples, and collection notes.
Laboratory tests may use blood, urine, stool, saliva, swabs, or specialized specimens depending on the health question and substance being measured.

The specimen must match the question. A pathogen test from blood may answer a different question than a swab from the site of symptoms; a urine marker may identify kidney damage that is not captured by a blood filtration estimate. Collection quality, timing, transport, and storage can be as important as the analytic method. [2]

SpecimenWhat it may measureCommon examplesPreparation or collection considerationsImportant limitations
Blood (whole blood, serum, or plasma)Cells, proteins, enzymes, hormones, antibodies, nutrients, electrolytes, medications, or genetic material.CBC, metabolic panels, lipids, glucose, A1C, thyroid tests, iron studies, antibody tests.The exact test may require fasting, a particular collection time, medication information, or avoiding strenuous exercise. Hydration can affect collection and some concentrations.A blood result is a sample from one point in time. It may be influenced by illness, timing, medications, supplements, fluid status, and laboratory method.
UrineCells, protein or albumin, glucose, ketones, blood, bacteria, hormones, drugs, and waste products.Urinalysis, urine culture, uACR, pregnancy testing, drug testing, 24-hour urine studies.Collection may require a clean-catch sample, first-morning specimen, timed collection, or complete 24-hour collection. Follow container and storage instructions.Contamination, hydration, exercise, menstruation, collection timing, and an incomplete timed collection can change results.
StoolVisible or occult blood, pathogens, inflammatory proteins, digestive markers, or parasite-related findings.Fecal immunochemical testing, pathogen testing, calprotectin, pancreatic elastase, ova and parasite testing.Avoid urine or toilet-water contamination. Some tests have diet or medication instructions; collection devices and storage rules differ.A negative result may not exclude intermittent bleeding or infection. Results must match symptoms, exposure, and other evaluation.
Saliva or cheek swabDNA, selected hormones, drugs, antibodies, or pathogen genetic material, depending on the assay.Genetic testing, selected infection tests, drug testing, and selected hormone tests.Food, drink, smoking, oral products, timing, and collection technique may matter. The mouth may need to be free of food or drink for a stated period.Saliva is not interchangeable with blood for every analyte. Method validation, timing, and specimen quality are critical.
Nasal, throat, genital, rectal, skin, or wound swabAntigen, organism growth, or microbial genetic material from a specific body site.Respiratory-virus tests, strep tests, STI NAATs, wound culture, and colonization screening.The correct anatomical site and collection technique matter. Antibiotics, antiseptics, and recent exposure timing may affect findings.A sample from the wrong site can miss an infection. Detection may represent colonization rather than the cause of symptoms.
BreathGases or labeled metabolic products produced after a test substance is given.H. pylori urea breath testing and hydrogen or methane breath testing.Fasting, diet, smoking, exercise, antibiotics, acid-suppressing drugs, and bowel-preparation timing may affect some tests.Breath tests answer focused questions and may have false-positive or false-negative results when preparation is incomplete.
Tissue, cells, or other body fluidsCell structure, proteins, organisms, chromosomes, DNA, or chemistry in a specific tissue or fluid.Biopsy pathology, cervical cytology, bone marrow, cerebrospinal fluid, synovial fluid, amniotic fluid.Many require clinician collection, sterile technique, local anesthesia, imaging guidance, or special handling.These procedures may be invasive and carry different risks. A blood test usually cannot substitute when tissue architecture or a site-specific sample is required.
Genetic sample (often blood, saliva, or cheek cells)DNA variants, chromosome changes, gene expression, or selected genomic patterns.Single-gene tests, multigene panels, carrier screening, pharmacogenomics, and hereditary-risk testing.Consent, identity, family history, sample quality, and pretest counseling may matter. Clinical confirmation may be needed after some consumer tests.A result may be positive, negative, uncertain, or inconclusive. It may not predict whether, when, or how severely a condition will occur.

Why Are Laboratory Tests Ordered?

Patient-centered lab test selection framework based on symptoms, history, life stage, medications, prior results, preparation, and follow-up.
Focused lab test selection starts with a clear health question and considers symptoms, history, medications, previous results, preparation, and follow-up.

The same laboratory test may serve different purposes. Knowing the purpose helps determine whether the test is appropriate, how it should be prepared for, and what follow-up is reasonable.

Screening

Screening looks for an important condition or risk before it is known to be present. Examples may include age- and risk-appropriate cholesterol, diabetes, prenatal, infection, or cancer screening. A screening test is not automatically appropriate for every person or at every interval.

Risk assessment

Risk-assessment tests contribute to an estimate rather than a diagnosis. Lipids, A1C, uACR, selected inflammatory markers, and hereditary-risk tests may change a risk discussion, but they must be combined with other factors.

Diagnostic support

When symptoms or examination findings raise a question, laboratory testing can narrow possibilities, identify patterns, or show whether a system is affected. The result may lead to repeat testing, imaging, functional testing, biopsy, referral, or a different diagnostic path.

Baseline testing

A baseline documents a value before treatment, pregnancy, a major training program, a medication change, or planned monitoring. A baseline is most useful when there is a reason to compare it with a later result.

Medication monitoring

Some medicines require testing for effectiveness, dose guidance, organ function, blood-cell effects, or other safety concerns. The needed test and timing depend on the medication and prescribing plan. Do not change a medicine because of this guide or one result.

Disease monitoring and follow-up

Repeated tests can track stability, response, recurrence risk, or complications. A meaningful trend usually requires comparable methods, known collection conditions, and a time interval appropriate to the biology and treatment.

Confirmatory testing

Unexpected or borderline results may be repeated under controlled conditions or confirmed with a different method. This reduces the chance that temporary biology, collection error, interference, or statistical variation drives an important decision.

Acute or emergency testing

Emergency departments and urgent-care settings use targeted tests—often together with vital signs, electrocardiography, imaging, and examination—to evaluate immediate threats. Troponin, blood gases, lactate, coagulation studies, toxicology, cultures, and other acute tests should not be presented as routine wellness testing. Symptoms suggesting a heart attack, stroke, severe infection, major bleeding, respiratory failure, pregnancy emergency, or other life-threatening condition require prompt care. [23]

Individual Tests Versus Lab Panels

Comparison of an individual lab test, lab panel, and testing profile with examples, strengths, limitations, and patient-centered selection guidance.
Individual tests answer focused questions, panels group related measurements, and testing profiles combine tests around a broader health question.

An individual test is usually best when one focused question has already been defined. A panel may be more efficient when several closely related measurements must be interpreted together. Neither format is automatically superior.

OptionPotential advantagesPotential limitationsBest selection question
Individual testFocused, easier to connect to one clinical question, fewer incidental findings, and may reduce unnecessary follow-up.May be incomplete when several markers must be interpreted together or when a reflex pathway is needed.Will this one measurement change the next decision?
Standard panelRelated tests are collected together and may reveal a useful pattern, such as electrolytes with kidney markers or red-cell indices with hemoglobin.Some components may not be relevant, and an isolated minor abnormality may trigger repeat testing.Are all components relevant to the same health question?
Large or custom panelMay be useful for a complex, preplanned evaluation or longitudinal program.More opportunities for incidental findings, false positives, conflicting markers, unclear actionability, and cost.Is there a plan for every result, including borderline and unexpected findings?

A “normal range” contains most values observed in a laboratory’s comparison population, not every value compatible with health. When many unrelated tests are ordered, the probability that at least one result falls outside its reference interval rises even when no disease is present. That is one reason the testing question—not the panel size—should guide selection. [1] [16]

Common Lab Tests and Blood Work Panels

Common lab tests and what they measure, including CBC, CMP, A1C, lipids, kidney, liver, thyroid, nutrient, and inflammation testing.
Common blood tests and lab panels evaluate different cells, chemicals, organs, nutrients, and risk markers; no single testing list is right for everyone.

The following matrix describes frequently used laboratory tests. It is not a universal checklist, and no adult should order every item simply because it appears here. The relevant combination depends on symptoms, history, age, life stage, medications, existing conditions, prior results, and the decision the testing is intended to support.

Test and specimenWhat it measures and why it may be orderedPreparation, limitations, and related resources
Test or panel: Complete blood count
Common abbreviation: CBC
Specimen: Blood
What it measures: Red cells, white cells, platelets, hemoglobin, hematocrit, and cell indices; a differential adds white-cell types.
Why it may be ordered: General health assessment; anemia, infection, inflammation, bleeding, marrow, or medication-monitoring questions.
Preparation considerations: Usually no fasting. Recent exercise, hydration, altitude, smoking, pregnancy, menstruation, and medicines may affect values.
What it cannot establish by itself: It does not identify the cause of an abnormal count by itself.
Related health pillar: CBC and Anemia Blood Tests
Verified Ulta Lab Tests page: CBC with differential and platelets
Test or panel: Comprehensive metabolic panel
Common abbreviation: CMP
Specimen: Blood
What it measures: Glucose, electrolytes, kidney-related markers, calcium, proteins, bilirubin, and liver-associated enzymes.
Why it may be ordered: Broad metabolic review, medication monitoring, dehydration or electrolyte questions, and kidney or liver diagnostic support.
Preparation considerations: Fasting may be requested when glucose or other paired tests require it. Hydration, exercise, illness, and medicines can matter.
What it cannot establish by itself: It cannot diagnose a specific kidney, liver, endocrine, or metabolic disease alone.
Related health pillar: Metabolic Health Blood Tests
Verified Ulta Lab Tests page: Comprehensive Metabolic Panel
Test or panel: Basic metabolic panel
Common abbreviation: BMP
Specimen: Blood
What it measures: Glucose, calcium, sodium, potassium, carbon dioxide, chloride, BUN, and creatinine.
Why it may be ordered: Electrolyte, glucose, fluid-balance, and kidney-function questions.
Preparation considerations: Fasting requirements depend on the clinical question and accompanying tests.
What it cannot establish by itself: It does not include the liver-associated tests and proteins found in a CMP.
Related health pillar: Kidney Function Tests
Verified Ulta Lab Tests page: Basic Metabolic Panel
Test or panel: Lipid panel
Common abbreviation: Lipid profile
Specimen: Blood
What it measures: Total cholesterol, HDL cholesterol, triglycerides, and calculated or measured LDL cholesterol.
Why it may be ordered: Cardiovascular risk assessment and monitoring of lifestyle or clinician-directed treatment.
Preparation considerations: Fasting is not always required, but it may be requested when triglycerides are a central question or by the ordering professional.
What it cannot establish by itself: It does not determine total cardiovascular risk or prove that plaque is present.
Related health pillar: Heart Health Blood Tests
Verified Ulta Lab Tests page: Lipid Panel
Test or panel: Glucose
Common abbreviation: FPG when fasting
Specimen: Blood
What it measures: Blood glucose at the time of collection.
Why it may be ordered: Screening or diagnostic support for glucose disorders, acute metabolic assessment, or medication monitoring.
Preparation considerations: Timing and fasting status must be known. Recent food, stress, illness, exercise, and medicines can affect it.
What it cannot establish by itself: One glucose value may not represent usual glucose exposure or establish a diagnosis without appropriate criteria and confirmation.
Related health pillar: Diabetes and Prediabetes Blood Tests
Verified Ulta Lab Tests page: Glucose test
Test or panel: Hemoglobin A1C
Common abbreviation: A1C or HbA1c
Specimen: Blood
What it measures: The percentage of hemoglobin with attached glucose, reflecting average exposure over roughly the prior two to three months.
Why it may be ordered: Screening, diagnostic support, and monitoring of diabetes or prediabetes when appropriate.
Preparation considerations: Fasting is generally not required. Conditions affecting red-cell lifespan, hemoglobin variants, anemia, kidney disease, pregnancy, or recent blood loss may affect interpretation.
What it cannot establish by itself: It does not show daily highs and lows and may be misleading in some blood or medical conditions.
Related health pillar: Diabetes and Prediabetes Blood Tests
Verified Ulta Lab Tests page: A1C test
Test or panel: Thyroid-stimulating hormone
Common abbreviation: TSH
Specimen: Blood
What it measures: A pituitary hormone that signals the thyroid and is commonly used as an initial thyroid-function test.
Why it may be ordered: Screening or evaluation of thyroid dysfunction and monitoring of clinician-directed thyroid treatment.
Preparation considerations: Timing, acute illness, pregnancy, biotin, and medications can matter. Do not change medication without instructions from the prescribing professional.
What it cannot establish by itself: TSH alone may not explain the cause, severity, or symptoms of every thyroid disorder.
Related health pillar: Thyroid Blood Tests
Verified Ulta Lab Tests page: TSH test
Test or panel: Free thyroxine
Common abbreviation: Free T4
Specimen: Blood
What it measures: The unbound portion of thyroxine, a main thyroid hormone.
Why it may be ordered: Used with TSH when thyroid dysfunction is suspected, when pituitary disease is a concern, or for selected monitoring questions.
Preparation considerations: Biotin and medications may interfere; pregnancy-specific interpretation may be needed.
What it cannot establish by itself: It does not identify autoimmune thyroid disease or explain every symptom by itself.
Related health pillar: Thyroid Blood Tests
Verified Ulta Lab Tests page: TSH and Free T4 test
Test or panel: Iron studies and ferritin
Common abbreviation: Iron, TIBC, saturation, ferritin
Specimen: Blood
What it measures: Circulating iron, iron-binding capacity, transferrin saturation, and stored-iron marker ferritin.
Why it may be ordered: Evaluation of iron deficiency, iron overload, anemia patterns, fatigue, blood loss, or treatment monitoring.
Preparation considerations: Iron varies by time and intake; fasting or morning collection may be requested. Ferritin can rise with inflammation, liver disease, infection, or other conditions.
What it cannot establish by itself: Ferritin is not a pure iron-storage measure in every setting, and one marker does not identify the cause of deficiency or excess.
Related health pillar: CBC and Anemia Blood Tests
Verified Ulta Lab Tests page: Ferritin, iron, and TIBC panel
Test or panel: Vitamin B12
Common abbreviation: B12 or cobalamin
Specimen: Blood
What it measures: Circulating vitamin B12; other markers may be used when results are borderline or symptoms persist.
Why it may be ordered: Evaluation of macrocytic anemia, neuropathy, dietary risk, malabsorption, or medication-related risk.
Preparation considerations: Supplements and injections can raise the result. Timing relative to treatment should be documented.
What it cannot establish by itself: A serum value alone may not explain symptoms or always establish functional deficiency.
Related health pillar: Vitamin and Nutrient Deficiency Tests
Verified Ulta Lab Tests page: Vitamin B12 test
Test or panel: Folate
Common abbreviation: Serum folate
Specimen: Blood
What it measures: Folate circulating in blood.
Why it may be ordered: Evaluation of macrocytosis, nutritional risk, malabsorption, pregnancy-related planning, or treatment monitoring.
Preparation considerations: Recent intake and supplementation can affect serum values.
What it cannot establish by itself: It does not replace evaluation for vitamin B12 deficiency or identify the cause of an abnormal result.
Related health pillar: Vitamin and Nutrient Deficiency Tests
Verified Ulta Lab Tests page: Serum folate test
Test or panel: 25-hydroxy vitamin D
Common abbreviation: 25(OH)D
Specimen: Blood
What it measures: The main circulating form used to assess vitamin D status.
Why it may be ordered: Evaluation of deficiency risk, bone or mineral questions, malabsorption, or clinician-directed supplementation monitoring.
Preparation considerations: Supplements, season, sun exposure, and some medical conditions affect levels. Testing frequency should match the clinical question.
What it cannot establish by itself: It does not by itself diagnose osteoporosis, explain pain, or establish a treatment target for every person.
Related health pillar: Vitamin and Nutrient Deficiency Tests
Verified Ulta Lab Tests page: Vitamin D, 25-hydroxy, total
Test or panel: Urinalysis
Common abbreviation: UA
Specimen: Urine
What it measures: Appearance, concentration, pH, protein, glucose, ketones, blood, cells, casts, crystals, and other findings depending on the method.
Why it may be ordered: Urinary symptoms, kidney or metabolic questions, pregnancy care, or general evaluation.
Preparation considerations: A clean-catch or first-morning specimen may be requested. Menstruation, exercise, hydration, and contamination can affect results.
What it cannot establish by itself: It does not identify every infection or kidney disease and may require culture, microscopy, imaging, or repeat testing.
Related health pillar: Kidney Function Tests
Verified Ulta Lab Tests page: Complete urinalysis
Test or panel: Creatinine, eGFR, and cystatin C
Common abbreviation: eGFRcr, eGFRcys
Specimen: Blood
What it measures: Filtration-related markers used to estimate kidney function.
Why it may be ordered: Kidney screening and monitoring, medication-safety questions, and confirmation when creatinine may be less reliable.
Preparation considerations: Hydration, muscle mass, diet, supplements, acute illness, and some medicines can affect markers. eGFR equations estimate rather than directly measure filtration.
What it cannot establish by itself: A single result does not establish chronic kidney disease; duration, urine findings, and clinical context matter.
Related health pillar: Kidney Function Tests
Verified Ulta Lab Tests page: eGFR with creatinine and cystatin C
Test or panel: Urine albumin-to-creatinine ratio
Common abbreviation: uACR
Specimen: Urine
What it measures: Albumin relative to creatinine in a spot urine sample.
Why it may be ordered: Early kidney-damage assessment, especially in diabetes, hypertension, or other risk settings.
Preparation considerations: Exercise, fever, infection, menstruation, marked hyperglycemia, and collection conditions can cause temporary elevations; repeat confirmation may be needed.
What it cannot establish by itself: It does not measure filtration and does not establish a cause of kidney injury.
Related health pillar: Kidney Function Tests
Verified Ulta Lab Tests page: Albumin Random Urine Test with Creatinine
Test or panel: Liver-associated tests
Common abbreviation: ALT, AST, ALP, GGT, bilirubin, albumin
Specimen: Blood
What it measures: Enzymes, pigments, and proteins related to liver cells, bile flow, and synthetic function.
Why it may be ordered: Evaluation of symptoms, medication effects, metabolic liver risk, viral hepatitis, or monitoring of known disease.
Preparation considerations: Exercise, alcohol, illness, fasting status, supplements, and medicines can influence results. Patterns are often more useful than one value.
What it cannot establish by itself: Abnormal enzymes do not by themselves identify the cause or measure fibrosis; normal enzymes do not exclude significant disease.
Related health pillar: Liver Function Tests
Verified Ulta Lab Tests page: Hepatic Function Panel
Test or panel: C-reactive protein
Common abbreviation: CRP or hs-CRP
Specimen: Blood
What it measures: A liver-produced protein that rises with inflammation; high-sensitivity methods can support selected cardiovascular-risk assessment.
Why it may be ordered: Evaluation of inflammation or infection and, in the appropriate setting, cardiovascular risk assessment.
Preparation considerations: Recent illness, injury, obesity, smoking, exercise, and chronic conditions may affect levels.
What it cannot establish by itself: It is nonspecific and cannot identify the location or cause of inflammation by itself.
Related health pillar: Inflammation and Autoimmune Blood Tests
Verified Ulta Lab Tests page: C-reactive protein test
Test or panel: Erythrocyte sedimentation rate
Common abbreviation: ESR or sed rate
Specimen: Blood
What it measures: How quickly red cells settle in a tube, an indirect marker influenced by inflammation and blood characteristics.
Why it may be ordered: Support for evaluating or monitoring selected inflammatory, infectious, or autoimmune conditions.
Preparation considerations: Age, pregnancy, anemia, kidney disease, and other factors may affect it.
What it cannot establish by itself: It is nonspecific and cannot confirm an autoimmune disease or infection alone.
Related health pillar: Inflammation and Autoimmune Blood Tests
Verified Ulta Lab Tests page: Sedimentation rate test

How Are Lab Tests Selected?

Good test selection begins with a decision, not a shopping list. This five-question framework can be used before routine, direct-access, or clinician-ordered testing.

  1. What decision should the test inform? Define whether the purpose is screening, risk assessment, diagnostic support, baseline measurement, confirmation, medication monitoring, or disease monitoring.
  2. Is the test appropriate for this person now? Consider symptoms, medical and family history, age, sex-related biology, pregnancy, life stage, exposures, medications, existing conditions, prior results, and evidence-based recommendations.
  3. What is the smallest sufficient test set? Select the individual test, standard panel, or staged pathway most likely to answer the question. Avoid adding unrelated markers simply because they are available.
  4. What could distort the result? Confirm fasting, time of day, exercise, hydration, acute illness, alcohol, smoking, menstrual-cycle timing, pregnancy, medications, biotin, supplements, and specimen instructions.
  5. What happens after each possible result? Plan for a normal, abnormal, borderline, inconsistent, or inconclusive finding. Decide who will review it, when repeat or confirmatory testing would be considered, and what symptoms require earlier care.

False-positive and false-negative results have different consequences. A low-risk screening situation may produce more false alarms than a targeted evaluation with a higher pretest probability. Conversely, a negative result can be falsely reassuring when the specimen, timing, or test does not match the suspected condition. Diagnostic stewardship means using the right test, for the right person, at the right time, with a clear interpretation and follow-up plan. [16]

What Lab Tests Can and Cannot Reveal

What lab tests can and cannot reveal, including screening, risk markers, monitoring, limitations, and when other medical evaluation may be needed.
Lab results can support screening, risk assessment, baseline testing, and monitoring, but they must be interpreted with clinical context.
Tests may helpTests generally cannot do aloneOther evaluation that may be needed
Measure a defined substance, cell, antibody, organism, genetic sequence, or other characteristic in a specimen.Provide a complete diagnosis without the history, examination, diagnostic criteria, and sometimes imaging or procedures.A clinical history, physical examination, repeat or confirmatory testing, imaging, functional testing, or specialist evaluation.
Identify patterns that support screening, risk assessment, diagnostic evaluation, baseline measurement, or monitoring.Explain every symptom or determine whether an abnormality is causing the symptom.Review of timing, medications, nutrition, sleep, exposures, mental health, and nonlaboratory causes.
Detect some changes before symptoms appear when an evidence-based screening strategy exists.Guarantee future health when results are within the laboratory reference interval.Age- and risk-appropriate preventive care, blood pressure, vaccination, examination, and recommended imaging or procedures.
Show changes over time when the same or comparable methods are used and collection conditions are understood.Make every difference between two results clinically meaningful.Assessment of biological variation, laboratory variation, preparation, treatment changes, and the size and persistence of the change.
Support medication monitoring when a recognized test and schedule apply.Tell a person to start, stop, or change a prescription without the prescribing clinician’s plan.Review with the prescribing professional and consideration of symptoms, dose, adherence, interactions, and other monitoring.
Provide hereditary, carrier, or pharmacogenomic information when a validated test is used.Predict with certainty whether a person will develop a condition, when it will appear, or how severe it will be.Pretest and post-test counseling, family-history review, clinical confirmation, and condition-specific surveillance decisions.

These limits are especially important in cancer testing. Blood counts, organ-function tests, tumor markers, and molecular tests may contribute useful information, but normal results can occur in people with cancer and abnormal results can occur for noncancerous reasons. Imaging, endoscopy, pathology, or biopsy may be required to establish a diagnosis or characterize a tumor. [17] [18]

How to Prepare for Laboratory Testing

Blood work preparation checklist covering instructions, fasting, hydration, timing, medications, supplements, biotin, and specimen collection.
Preparation requirements vary by test. Follow the exact instructions and do not change medication unless directed by the prescribing professional.

Follow the instructions for the exact test ordered. Preparation rules are not interchangeable, and fasting when it is not required can be inconvenient or occasionally unsafe for some people. Ask the ordering professional or laboratory when instructions are unclear. [2] [3]

Preparation checklist

  • Confirm the order: Review every test, specimen type, fasting requirement, collection time, location, and any special kit or container.
  • Fasting: Fast only when instructed. Confirm whether plain water is allowed, how many hours are required, and how diabetes or other medical needs should be handled.
  • Hydration: Unless instructed otherwise, normal hydration can make blood collection easier. Excessive water intake can dilute some urine results.
  • Time of day: Some hormones, iron measurements, cortisol-related tests, medication levels, and other analytes vary by time. Use the requested window.
  • Exercise: Strenuous activity can temporarily affect muscle enzymes, kidney-related markers, liver-associated enzymes, glucose, white-cell counts, and urine findings. Follow test-specific restrictions.
  • Acute illness: Fever, infection, injury, surgery, dehydration, and inflammation can change many markers. Record the circumstance and ask whether routine baseline testing should be postponed.
  • Alcohol and smoking: Both can affect selected results. Follow any stated avoidance period rather than inventing a universal rule.
  • Menstrual-cycle timing: Reproductive hormones and some urine or stool collections may require cycle timing or documentation of bleeding.
  • Pregnancy: Pregnancy changes reference intervals and affects test selection. Tell the ordering professional and laboratory when pregnant or possibly pregnant.
  • Medications: Provide a complete list, including dose and collection timing when relevant. Do not stop or change prescription or over-the-counter medication unless the prescribing or ordering professional specifically instructs you.
  • Biotin: High-dose biotin in supplements can interfere with some laboratory assays and produce incorrect results. Tell the laboratory and healthcare professional what you take and follow their instructions. [15]
  • Vitamins, supplements, and energy products: Record all products, including powders, gummies, injections, herbal products, and pre-workout formulas. Supplements can change the measured level or interfere with the method.
  • Specimen-specific collection: Use the correct container, clean-catch or timing method, storage temperature, transport window, and collection site. An incomplete 24-hour urine or contaminated stool sample may need to be repeated.

What Happens After Testing?

Results may be released as numbers, positive or negative findings, detected or not detected, interpretive comments, or pathology and molecular reports. A high or low flag means the value is outside that laboratory’s stated reference interval; it does not automatically mean the result is dangerous or diagnostic. Reference intervals can vary with method, laboratory, age, sex-related biology, pregnancy, and other factors. [1]

Review the reason for testing, the full pattern, prior results, preparation, units, and the magnitude and persistence of change. A result may need repeat testing when it is unexpected, inconsistent with symptoms, near a decision threshold, affected by preparation, or known to vary biologically. A different confirmatory test may be needed when the first method is a screen or when interference is possible.

For a complete interpretation workflow, read how to read and understand laboratory results, including reference intervals, diagnostic thresholds, abnormal flags, trends, ratios, repeat testing, and questions to discuss with a healthcare professional.

When results are available, you can view and track your lab results in the secure patient portal. Review the complete report, including units, reference information, comments, and prior results, before deciding what follow-up question to ask.

How Can Patients Access Laboratory Testing?

Laboratory testing may be ordered through a physician or other authorized professional, a health system, an urgent-care or emergency setting, a public-health program, or a direct-access service where permitted. Requirements vary by test, state law, laboratory policy, specimen, age, pregnancy status, and clinical risk. Some tests require an in-person examination, counseling, clinician collection, imaging guidance, or a specialist.

Routine direct-access testing is not an appropriate response to severe or rapidly worsening symptoms. It also does not replace a healthcare professional when diagnosis, treatment, medication management, or urgent evaluation is needed.

For the patient journey from selection through follow-up, see how direct-access laboratory testing works and what to expect.

Explore Lab Testing by Health Category

Map of 19 lab testing health areas, including cardiovascular, metabolic, hormone, nutrition, immunity, brain, aging, and genetic testing.
Explore 19 laboratory testing categories spanning cardiometabolic, hormonal, reproductive, nutritional, immune, neurological, aging, and genetic health.

Use this directory to move from a broad question about laboratory testing to the health area that best matches the reason for testing. Each pillar explains the relevant biomarkers, common panels, preparation, limitations, and follow-up questions in greater depth.

Cardiometabolic and Organ Health

  • Heart Health Blood Tests — Explains cholesterol and triglycerides, ApoB, lipoprotein(a), glucose-related risk, inflammation markers, and other laboratory information used with history, blood pressure, examination, and cardiovascular risk assessment.
  • Diabetes and Prediabetes Blood Tests — Covers glucose, hemoglobin A1C, insulin, C-peptide, urine albumin, and related tests used for screening, risk assessment, diagnostic support, and monitoring of blood-sugar disorders.
  • Metabolic Health Blood Tests — Organizes insulin, glucose, lipids, liver, kidney, thyroid, nutritional, and medication-safety questions that may arise during weight management or clinician-directed GLP-1 therapy.
  • Kidney Function Tests — Explains creatinine, estimated glomerular filtration rate (eGFR), cystatin C, urine albumin-to-creatinine ratio (uACR), electrolytes, and urinalysis, including why trends and repeat measurements matter.
  • Liver Function Tests — Reviews ALT, AST, alkaline phosphatase, GGT, bilirubin, albumin, platelet count, viral hepatitis testing, and noninvasive fibrosis-risk tools without treating one enzyme value as a diagnosis.

Hormonal and Reproductive Health

  • Thyroid Blood Tests — Explains TSH, free T4, free T3, thyroid antibodies, and the roles of screening, confirmation, medication monitoring, pregnancy, and symptom-directed thyroid evaluation.
  • Women’s Hormone Blood Tests — Covers estradiol, progesterone, FSH, LH, AMH, testosterone, prolactin, thyroid testing, and metabolic markers in questions involving cycles, menopause, ovarian reserve, and PCOS.
  • Men’s Health Blood Tests — Explains total and free testosterone, SHBG, estradiol, LH, FSH, prolactin, PSA, blood counts, and metabolic markers used in men’s health and clinician-directed hormone monitoring.
  • Fertility and Preconception Lab Tests — Organizes ovarian-reserve, ovulation, thyroid, prolactin, infectious-disease, nutritional, genetic-carrier, and male fertility questions before conception or during a fertility evaluation.
  • Pregnancy Blood Tests and Prenatal Screening — Introduces blood type, blood counts, immunity and infection testing, glucose screening, thyroid testing, and other clinician-directed prenatal tests, while distinguishing routine prenatal care from urgent pregnancy evaluation.

Nutrition, Digestion, and Blood Health

  • Vitamin and Nutrient Deficiency Tests — Explains vitamin D, vitamin B12, folate, iron, ferritin, magnesium, zinc, and other nutrient markers, including when a blood level is informative and when symptoms or diet alone are insufficient.
  • Digestive Health Lab Tests — Covers blood, stool, breath, and antibody testing for questions involving celiac disease, inflammation, infection, malabsorption, pancreatic function, liver involvement, and nutrient status.
  • CBC and Anemia Blood Tests — Explains red cells, white cells, platelets, hemoglobin, hematocrit, MCV, reticulocytes, ferritin, iron studies, vitamin B12, and folate in anemia and blood-count evaluation.

Inflammation, Cancer, and Infection

  • Inflammation and Autoimmune Blood Tests — Reviews CRP, hs-CRP, ESR, ANA, rheumatoid factor, anti-CCP, complement, and selected disease-specific antibodies, emphasizing that inflammatory and autoimmune markers require clinical context.
  • Cancer Blood Tests and Tumor Markers — Explains appropriate uses and important limitations of blood counts, organ-function tests, tumor markers, hereditary-risk tests, and monitoring tests. It does not imply that a blood test can independently rule in or rule out every cancer.
  • Infectious Disease Testing — Explains antibody, antigen, culture, PCR, NAAT, immunity-titer, and sexually transmitted infection testing, including timing, specimen-site selection, window periods, and confirmatory testing.

Brain Health, Aging, and Genomics

  • Brain and Neurological Blood Tests — Organizes laboratory questions related to memory, migraine, neuropathy, nutrient deficiencies, thyroid and metabolic contributors, medication effects, and selected neurological biomarkers while recognizing the central role of examination and imaging.
  • Healthy Aging and Longevity Blood Tests — Covers bone and mineral health, muscle injury and recovery, hydration, cardiometabolic risk, hormones, nutrition, fitness, and longitudinal monitoring, with focused testing rather than indiscriminate “anti-aging” panels.
  • Genetic and Genomic Testing — Explains single-gene and multigene testing, chromosomes, hereditary risk, carrier screening, pharmacogenomics, result classifications, variants of uncertain significance, counseling, privacy, and the difference between clinical and consumer DNA reports.

When Routine Testing Is Not Enough

Routine laboratory testing can miss conditions that require a physical examination, vital signs, imaging, electrocardiography, pulmonary or neurological testing, endoscopy, biopsy, or a specimen from the actual site of disease. It may also delay care when symptoms are urgent.

Seek prompt medical attention for severe, sudden, rapidly worsening, or potentially life-threatening symptoms. Examples include chest pressure or pain, severe trouble breathing, signs of stroke, fainting, new severe confusion, uncontrolled bleeding, a severe allergic reaction, major trauma, seizures, severe dehydration, suicidal thoughts, or concerning pregnancy symptoms. In the United States, call 911 for an emergency. This list is not exhaustive.

Persistent symptoms also deserve evaluation even when routine blood work is within range. A normal CBC, CMP, thyroid test, or inflammatory marker cannot rule out every heart, neurological, gastrointestinal, hormonal, infectious, autoimmune, or malignant condition.

How Ulta Lab Tests May Help

Where direct-access testing is permitted, Ulta Lab Tests allows eligible customers to select and purchase laboratory tests online. An authorization is included, specimens are collected at participating Quest Diagnostics patient service locations, and results are delivered through a secure online account. Ulta states that most routine results are typically available within one to two business days, although timing varies by test and complex testing may take longer. HSA or FSA funds may be used for eligible purchases.

Direct-access laboratory testing through Ulta Lab Tests is currently unavailable in Hawaii, New York, New Jersey, and Rhode Island because of state restrictions. Availability, collection locations, test components, preparation, and result timing should be confirmed on the current product and policy pages before ordering.

Ulta Lab Tests provides access to testing; it does not diagnose a condition, prescribe treatment, replace urgent care, or substitute for a healthcare professional when an examination or individualized medical decision is needed.

Questions to Ask a Healthcare Professional

  1. What specific question is this test intended to answer?
  2. Is the test being used for screening, diagnostic support, confirmation, baseline measurement, or monitoring?
  3. Would one focused test, a standard panel, or a staged testing plan be most appropriate?
  4. Do my symptoms, family history, age, pregnancy status, medications, or prior results change which test is useful?
  5. Do I need to fast, collect at a particular time, avoid strenuous exercise, or follow special specimen instructions?
  6. Could any prescription, over-the-counter medicine, vitamin, biotin product, supplement, or recent treatment interfere?
  7. What result would change the next step, and what would not?
  8. When would a repeat or confirmatory test be appropriate?
  9. Which symptoms should prompt urgent care rather than waiting for a routine result?
  10. Who will review the result, and how will it be compared with prior values and the laboratory’s method?
  11. Could this test create an incidental finding that leads to additional procedures?
  12. For genetic testing, should I meet with a genetic counselor before or after testing, and could the result affect relatives?

Frequently Asked Questions About Lab Tests and Blood Work

What are the most common blood tests?

Common blood work includes a CBC, BMP or CMP, lipid panel, glucose or A1C, TSH, and selected tests based on symptoms or risk, such as iron studies, vitamin B12, vitamin D, liver-associated tests, kidney markers, or inflammation markers. There is no single universal list that every adult needs.

What is the difference between a lab test and a panel?

An individual test usually measures one analyte or one focused process. A panel groups related measurements, such as a CBC, BMP, CMP, or lipid panel. The exact components matter more than the marketing name.

Does every blood test require fasting?

No. Some tests are commonly collected without fasting, while others may require fasting because of the analyte, the clinical question, or an accompanying test. Follow the instructions for the exact order. [3]

Can normal blood work rule out disease?

No. A normal result may lower concern for a condition that the test is designed to detect, but it does not guarantee health or exclude diseases that require different tests, imaging, examination, or tissue sampling.

Does an abnormal result mean I have a disease?

Not necessarily. Results can be temporarily abnormal because of illness, exercise, hydration, medicines, supplements, pregnancy, collection problems, biological variation, or laboratory variation. The size, pattern, persistence, and clinical context determine significance.

Why would a laboratory test need to be repeated?

Repeat testing may confirm an unexpected result, control preparation conditions, show whether a change persists, monitor treatment, or compare a trend. Sometimes a different confirmatory method is more appropriate than repeating the same test.

Can I order laboratory testing myself?

Direct-access testing is available for many tests in some jurisdictions, but rules and eligible tests vary. Some testing still requires a treating clinician, counseling, a physical examination, or a specialized collection. Ulta Lab Tests currently does not offer direct-access testing in Hawaii, New York, New Jersey, or Rhode Island.

Are larger lab panels better?

No. A larger panel can be useful when every component relates to a defined question and there is a follow-up plan. Otherwise, it increases the chance of incidental abnormalities, conflicting results, and unnecessary follow-up.

How often should blood work be done?

Frequency depends on the purpose, age, risk, pregnancy, symptoms, medication, existing conditions, prior findings, and guideline. Annual testing is not automatically necessary for every marker, and some monitoring requires a shorter or longer interval.

What can affect blood test results?

Food, fasting duration, hydration, time of day, posture, exercise, acute illness, alcohol, smoking, pregnancy, menstrual-cycle timing, medications, vitamins, supplements, biotin, specimen handling, and laboratory method can affect selected results.

What should I do with an abnormal result?

First review the test purpose, units, reference interval, preparation, medications, symptoms, and prior values. Do not change treatment on your own. Contact an appropriate healthcare professional, especially when the result is markedly abnormal, unexpected, or accompanied by concerning symptoms.

What is the difference between a reference interval and a diagnostic threshold?

A reference interval describes the values found in a defined comparison population using a particular method. A diagnostic threshold is a criterion supported by evidence or guidelines for a specific condition. A treatment or monitoring target is yet another concept and may be individualized. [1]

Can genetic testing predict my future health?

Some genetic tests identify variants associated with a hereditary condition, carrier status, or medication response. A result may not predict whether a condition will develop, the age of onset, or severity. Results can be uncertain, and family history, counseling, clinical confirmation, and non-genetic factors remain important. [19] [20] [21]

Are at-home and direct-to-consumer tests the same as clinical laboratory testing?

No. Tests differ in intended use, specimen collection, laboratory method, regulatory status, clinical validity, and whether a healthcare professional or confirmatory test is needed. Review what a product can and cannot establish before acting on the result. [22]

Conclusion: Choose Lab Tests to Answer a Clear Health Question

Lab tests can measure cells, chemistry, hormones, antibodies, organisms, nutrients, genetic material, and other biological characteristics. They can support screening, risk assessment, diagnostic evaluation, baseline measurement, confirmation, and monitoring—but they do not replace clinical context. Focused test selection is usually more useful than the largest available panel, and preparation, specimen quality, method, trends, and follow-up all affect what a result can contribute.

Next, learn how to understand laboratory values, ranges, flags, and trends or review how to select, order, prepare for, and follow up on direct-access testing. To explore a particular concern, use the 19-category laboratory testing directory above.

References

  1. How to Understand Your Lab Results. MedlinePlus. Updated 2025-09-04.
  2. How to Prepare for a Lab Test. MedlinePlus. Updated 2024-08-20.
  3. Fasting for a Blood Test. MedlinePlus. Updated 2025-08-28.
  4. Complete Blood Count (CBC). MedlinePlus. Updated 2024-10-15.
  5. Basic Metabolic Panel (BMP). MedlinePlus. Updated 2024-09-10.
  6. Comprehensive Metabolic Panel (CMP). MedlinePlus. Updated 2023-12-04.
  7. Hemoglobin A1C (HbA1c) Test. MedlinePlus. Accessed 2026-08-07.
  8. Thyroid Tests. MedlinePlus. Accessed 2026-08-07.
  9. Iron Tests. MedlinePlus. Accessed 2026-08-07.
  10. Vitamin B Test. MedlinePlus. Accessed 2026-08-07.
  11. Vitamin D Test. MedlinePlus. Updated 2024-12-04.
  12. Urinalysis. MedlinePlus. Updated 2024-10-09.
  13. NIDDK: Assess Urine Albumin. National Institute of Diabetes and Digestive and Kidney Diseases. Accessed 2026-08-07.
  14. C-Reactive Protein (CRP) Test. MedlinePlus. Accessed 2026-08-07.
  15. Biotin Interference with Troponin Lab Tests. U.S. Food and Drug Administration. Updated 2022-06-21.
  16. Diagnostic Stewardship: Preventing Diagnostic Error and Overuse. Agency for Healthcare Research and Quality. Accessed 2026-08-07.
  17. Tests and Procedures Used to Diagnose Cancer. National Cancer Institute. Updated 2023-01-17.
  18. Tumor Markers. National Cancer Institute. Updated 2023-12-07.
  19. Genetic Testing. MedlinePlus Genetics. Updated 2025-08-13.
  20. What are the different types of genetic tests? MedlinePlus Genetics. Updated 2021-07-28.
  21. What are the risks and limitations of genetic testing? MedlinePlus Genetics. Updated 2021-07-28.
  22. Direct-to-Consumer Tests. U.S. Food and Drug Administration. Accessed 2026-08-07.
  23. Troponin Test. MedlinePlus. Updated 2023-10-30.

Authorship, Disclosure, and Update History

Author: John R.

Ulta Lab Tests offers laboratory-testing services and may link to tests or panels discussed on this page. This content is educational and does not provide individual diagnosis or treatment.

Update history: August 7, 2026 — Repaired citation and same-page navigation targets; added stable section IDs and a concise table of contents; revalidated companion, product, and source links; added the results-tracking route; and rebuilt every table for accessible, mobile-usable light-blue presentation.

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