Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

Thyroid Panel


At a Glance

Why Get Tested?

To help evaluate thyroid gland function and to help diagnose thyroid disorders

When to Get Tested?

When you have signs and symptoms suggesting hypo- or hyperthyroidism due to a condition affecting the thyroid

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None needed; however, certain medications can interfere with the tests included in the panel, so tell your health practitioner about any drugs that you are taking.

The Test Sample

What is being tested?

A thyroid panel is a group of tests that may be ordered together to help evaluate thyroid gland function and to help diagnose thyroid disorders. The tests included in a thyroid panel measure the amount of thyroid hormones in the blood. These hormones are chemical substances that travel through the blood and control or regulate the body's metabolism—how it functions and uses energy.

The thyroid panel usually includes:

  • TSH (thyroid-stimulating hormone) – to test for hypothyroidism, hyperthyroidism and to monitor treatment for a thyroid disorder
  • Free T4 (thyroxine) – to test for hypothyroidism and hyperthyroidism; may also be used to monitor treatment
  • Free T3 or total T3 (triiodothyronine) – to test for hyperthyroidism; may also be used to monitor treatment

Sometimes a T3 resin uptake (T3RU) test is included to calculate, along with the T4 value, the free thyroxine index (FTI), another method for evaluating thyroid function that corrects for changes in certain proteins that can affect total T4 levels.

Pituitary-Thyroid Feedback System

TSH is produced by the pituitary gland and is part of the body's feedback system to maintain stable amounts of the thyroid hormones T4 and T3 in the blood. When thyroid hormone levels decrease, the pituitary is stimulated to release TSH. TSH in turn stimulates the production and release of T4 and T3 by the thyroid gland. When the system is functioning normally, thyroid production turns on and off to maintain constant blood thyroid hormone levels.

T3 and T4 are the two major hormones produced by the thyroid gland, a small butterfly-shaped organ that lies flat across the windpipe at the base of the throat. Together they help control the rate at which the body uses energy. Almost all of the T3 and T4 circulating in the blood is bound to protein. The small portions that are not bound or "free" are the biologically active forms of the hormones. Tests can measure the amount of free T3 or free T4 or the total T3 or total T4 (bound plus unbound) in the blood.

The total T4 and total T3 tests have been used for many years, but they can be affected by the amount of protein available in the blood to bind to the hormone. The free T4 and free T3 tests are not affected by protein levels and are thought by many to be more accurate reflections of thyroid hormone function. In most cases, the free T4 test has replaced that of the total T4 test. However, some professional guidelines recommend the total T3 test, so either total T3 or free T3 test may be used to assess thyroid function.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. Certain medications can interfere with the tests included in the panel, however, so tell the health practitioner about any drugs being taken.

The Test