FT3, FT4, RT3 and TSH Panel

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.

Also known as: Thyroid Stimulating Hormone, Thyroid Stimulating Hormone (TSH), Thyrotropin


A TSH test is a lab test that measures the amount of thyroid stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland. It tells the thyroid gland to make and release thyroid hormones into the blood.


*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 and TSH Panel panel contains 4 tests with 5 biomarkers.

Brief Description: The FT3, FT4, RT3, and TSH Panel is a targeted assessment designed to provide a comprehensive understanding of thyroid gland function and its regulatory mechanisms. By measuring the levels of free triiodothyronine (FT3), free thyroxine (FT4), reverse triiodothyronine (RT3), and thyroid-stimulating hormone (TSH), this panel offers insight into the intricate balance of thyroid hormone production, conversion, and overall endocrine health.

Collection Method: Blood Draw

Specimen Type: Serum

Test Preparation: Specific to TSH: Specimen collection after fluorescein dye angiography should be delayed for at least 3 days. For patients on hemodialysis, specimen collection should be delayed for 2 weeks.

According to the assay manufacturer Siemens: "Samples containing fluorescein can produce falsely depressed values when tested with the Advia Centaur TSH3 Ultra assay."

When and Why It May Be Ordered

This panel is typically ordered when symptoms suggest thyroid dysfunction, such as unexpected weight changes, mood fluctuations, changes in energy levels, or when monitoring the effectiveness of thyroid disorder treatments. It provides a detailed view of how well the thyroid gland is functioning and can help identify issues with hormone conversion or the influence of pituitary gland activity on the thyroid.

Test Descriptions and What They Check For

  • T3 Reverse (RT3): RT3 is an inactive form of the hormone T3. High levels can indicate that the body is converting too much FT3 into RT3, often a response to stress, illness, or other metabolic disturbances, impacting energy levels and metabolism.

  • T3 Free (FT3): FT3 measures the unbound, active form of triiodothyronine. FT3 levels can help diagnose hyperthyroidism or hypothyroidism, providing insight into the body's metabolic rate and overall energy regulation.

  • T4 Free (FT4): FT4 evaluates the free, unbound thyroxine levels in the blood. It's essential for diagnosing thyroid disorders, as T4 is the primary hormone produced by the thyroid gland, influencing metabolism, heart rate, and growth.

  • Thyroid Stimulating Hormone (TSH): TSH is produced by the pituitary gland and regulates the production of thyroid hormones. Abnormal levels can indicate primary hypothyroidism (high TSH) or hyperthyroidism (low TSH), reflecting the pituitary gland's response to thyroid gland activity.

Detected Conditions and Diseases

This panel can detect conditions such as:

  • Hyperthyroidism: Characterized by low TSH and high FT3 and FT4 levels.
  • Hypothyroidism: Indicated by high TSH and low FT3 and FT4 levels.
  • Thyroid Hormone Conversion Issues: Imbalances in RT3 levels can suggest problems with thyroid hormone conversion, often secondary to other health issues.

Clinical Applications

Healthcare professionals use this panel to:

  • Diagnose Thyroid Disorders: Differentiating between types of thyroid dysfunctions.
  • Monitor Treatment Efficacy: Adjusting thyroid hormone replacement or suppressive therapy.
  • Evaluate Metabolic Health: Understanding how thyroid function impacts overall metabolism and energy levels.

The FT3, FT4, RT3, and TSH Panel is a crucial tool in the diagnosis and management of thyroid-related disorders. By offering a detailed view of both the production and regulation of thyroid hormones, this panel assists healthcare professionals in crafting tailored treatment plans, ensuring optimal thyroid health and overall well-being for their patients.

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

Customer Reviews