FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel

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The following is a list of what is included in the item above. Click the test(s) below to view what biomarkers are measured along with an explanation of what the biomarker is measuring.

Also known as: Reverse T3, Reverse Triiodothyronine, RT3, T3 Reverse RT3 LCMSMS, Triiodothyronine Reverse

T3 Reverse, LC/MS/MS

Reverse T3 produced in the thyroid comes from the conversion of the storage hormone T4. Your body, especially the liver, can constantly be converting T4 to RT3 as a way to get rid of any unneeded T4. In any given day approx. 40% of T4 goes to T3 and 20% of T4 goes to Reverse T3. However in any situation where your body needs to conserve energy and focus on something else, it will change the above percentages, changing the conversion of RT3 to 50% or more, and the T3 goes down, down. Examples are emotional, physical, or biological stress, such as being chronically or acutely sick (the flu, pneumonia, etc), after surgery, after a car accident or any acute injury, chronic stress causing high cortisol, being exposed to an extremely cold environment, diabetes, aging, or even being on drugs like beta blockers and amiodarone.

Also known as: Free T3, FT3, T3 Free

T3, Free

This test measures the amount of triiodothyronine, or T3, in the blood.

Also known as: Free T4, FT4, T4 Free

T4, Free

The free T4 test is not affected by protein levels. Since free T4 is the active form of thyroxine, the free T4 test is may be a more accurate reflection of thyroid hormone function.

Thyroglobulin Antibodies

Measurement of thyroglobulin antibodies is useful in the diagnosis and management of a variety of thyroid disorders including Hashimoto's thyroiditis, Graves Disease and certain types of goiter.

Thyroid Peroxidase

*Important Information on Lab Test Processing Times: Ulta Lab Tests is committed to informing you about the processing times for your lab tests processed through Quest Diagnostics. Please note that the estimated processing time for each test, indicated in business days, is based on data from the past 30 days across the 13 Quest Diagnostics laboratories for each test. These estimates are intended to serve as a guide and are not guarantees. Factors such as laboratory workload, weather conditions, holidays, and the need for additional testing or maintenance can influence actual processing times. We aim to offer estimates to help you plan accordingly. Please understand that these times may vary, and processing times are not guaranteed. Thank you for choosing Ulta Lab Tests for your laboratory needs.

The FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel panel contains 4 tests with 5 biomarkers.

Brief Description: The FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel is a comprehensive diagnostic tool designed to evaluate thyroid function and identify autoimmune thyroid diseases. This panel includes tests that measure thyroid hormone levels, assess the conversion of these hormones, and detect antibodies that may indicate an autoimmune response against the thyroid gland. By providing a detailed overview of thyroid health, this panel helps healthcare providers diagnose and manage various thyroid-related conditions effectively.

Collection Method: Blood Draw

Specimen Type: Serum

Test Preparation: No preparation required

When and Why the FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel May Be Ordered

This panel may be ordered when a patient presents with symptoms suggestive of thyroid dysfunction, such as fatigue, weight changes, temperature sensitivity, hair loss, or mood alterations. It is also commonly recommended for individuals with a family history of thyroid disease, those with known autoimmune disorders, or patients who have had inconsistent thyroid function test results. The panel is valuable in diagnosing both hypo- and hyperthyroid conditions and identifying autoimmune thyroid diseases like Hashimoto's thyroiditis and Graves' disease.

What the FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel Checks For

The FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel includes several critical tests that provide insights into various aspects of thyroid health:

T3 Reverse

Reverse T3 (RT3) is an inactive form of triiodothyronine (T3) that can block the action of active T3. Measuring RT3 levels helps assess the body’s conversion efficiency from T4 to the active T3 versus the inactive RT3. Elevated RT3 can indicate issues such as stress, illness, or other conditions that affect thyroid hormone conversion.

T3 Free

Free T3 (FT3) measures the unbound fraction of T3 hormone available in the bloodstream to the tissues. FT3 is critical for regulating metabolism and is more biologically active than T4. Abnormal levels can indicate hyperthyroidism or hypothyroidism.

T4 Free

Free T4 (FT4) measures the unbound fraction of thyroxine (T4) in the blood, providing a clear picture of the thyroid’s production of this hormone. FT4 is converted into the more active T3 in the body. Imbalances in FT4 levels can indicate various thyroid disorders.

Thyroid Peroxidase Antibodies

Thyroid Peroxidase (TPO) antibodies are directed against the thyroid peroxidase enzyme, which is crucial for thyroid hormone production. The presence of TPO antibodies suggests an autoimmune response against the thyroid gland, commonly seen in Hashimoto’s thyroiditis and Graves’ disease.

Thyroglobulin Antibodies

Thyroglobulin (Tg) antibodies target thyroglobulin, a protein involved in thyroid hormone production. Elevated Tg antibodies indicate an autoimmune attack on the thyroid and are often present in autoimmune thyroid diseases like Hashimoto’s thyroiditis.

Conditions or Diseases the FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel Can Detect

The FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel is essential for detecting various thyroid-related conditions:


Hypothyroidism is characterized by an underactive thyroid gland that produces insufficient thyroid hormones. Symptoms include fatigue, weight gain, and depression. Low levels of FT3 and FT4, along with elevated TPO and Tg antibodies, can indicate hypothyroidism, particularly autoimmune hypothyroidism such as Hashimoto’s thyroiditis.


Hyperthyroidism involves an overactive thyroid gland that produces excessive thyroid hormones, leading to symptoms like weight loss, anxiety, and palpitations. High levels of FT3 and FT4 can indicate hyperthyroidism. Elevated TPO antibodies may be present in autoimmune hyperthyroidism, such as Graves’ disease.

Hashimoto's Thyroiditis

Hashimoto's Thyroiditis is an autoimmune disorder where the immune system attacks the thyroid gland, causing chronic inflammation and leading to hypothyroidism. The presence of TPO and Tg antibodies, along with low FT3 and FT4 levels, confirms this diagnosis.

Graves' Disease

Graves' Disease is an autoimmune condition that causes hyperthyroidism. High FT3 and FT4 levels, along with the presence of TPO antibodies, are indicative of Graves’ disease. Symptoms include goiter, exophthalmos, and increased metabolic rate.

Using the Results of the FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel


Healthcare professionals use the results of FT3, FT4, and antibody levels to diagnose hypothyroidism. Treatment typically involves thyroid hormone replacement therapy, and regular monitoring of hormone levels ensures the effectiveness of the treatment and helps adjust dosages as needed.


In cases of hyperthyroidism, elevated FT3 and FT4 levels guide the treatment plan, which may include antithyroid medications, radioactive iodine therapy, or surgery. Regular monitoring helps assess the response to treatment and make necessary adjustments.

Hashimoto's Thyroiditis

For Hashimoto’s Thyroiditis, the presence of TPO and Tg antibodies confirms the autoimmune nature of the disease. Treatment focuses on managing hypothyroidism through hormone replacement and monitoring antibody levels to track disease progression.

Graves' Disease

Graves’ Disease diagnosis involves elevated FT3 and FT4 levels and the presence of TPO antibodies. Treatment options include antithyroid drugs, radioactive iodine, and sometimes surgery. Monitoring these levels helps manage the condition and adjust treatments accordingly.

The FT3, FT4, RT3, TPO and Thyroglobulin Ab Panel provides a comprehensive assessment of thyroid health, crucial for diagnosing and managing various thyroid disorders. By evaluating hormone levels and detecting autoimmune antibodies, this panel enables healthcare providers to develop effective treatment strategies and monitor disease progression. Regular testing ensures optimal thyroid function and helps prevent complications, thereby supporting overall health and well-being.

We advise having your results reviewed by a licensed medical healthcare professional for proper interpretation of your results.

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