The Top 10 Thyroid Lab Tests

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.

Triiodothyronine (T3) is a thyroid hormone. It plays an important role in the body's control of metabolism.

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

FTI stands for the Free Thyroxine Index and is also sometimes referred to as T7. It is a calculated value determined from the T3 uptake test and total T4 test and provides an estimate of the level of free T4 in the blood.

This test measures the amount of thyroxine, or T4, in the blood. T4 is one of two major hormones produced by the thyroid gland. The total T4 test is used to help diagnose hyperthyroidism and hypothyroidism. It is a useful test but can be affected by the amount of protein available in the blood to bind to the hormone.

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.

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.

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.