THYROID TESTING

With our Thyroid Panels you will be able to evaluate your hormone production in your body.

Your thyroid gland is found in the front of the neck and produces chemicals known as hormones. These hormones basically regulate how our bodies operate in terms of utilization of food and energy. A normal thyroid gland produces a chemical called thyroxine. Based on the amount it produces, this will affect how the body functions, i.e. how it metabolizes the food we eat, and in turn how the body grows, and also reproduces.

The most common thyroid test is the blood test that measures the amount of thyroid-stimulating hormone (TSH) in your bloodstream. The test is sometimes called the thyrotropin-stimulating hormone test.

TSH that is elevated, or above normal, is considered indicative of hypothyroidism. TSH that is "suppressed" or below normal, is considered evidence of hyperthyroidism.

Free T4 / Free Thyroxine

Free T4 measures the free, unbound thyroxine levels in your bloodstream. Free T4 is typically elevated in hyperthyroidism, and lowered in hypothyroidism.

Free or unbound T4 levels represent the level of hormone available for uptake and use by cells. Bound levels represent a circulating hormone that may not all be immediately available, because it is affected by other drugs, illness, and physical changes such as pregnancy. Because the free levels of T4 represent immediately available hormone, free T4 is thought to better reflect the patient's hormonal status than total T4 (below).

Total T4/Total Thyroxine

This test measures the total amount of circulating thyroxine in your blood. Thyroxine, a hormone produced by the thyroid, is also known as T4. A high value can indicate hyperthyroidism, a low value can indicate hypothyroidism. Total T4 levels can be elevated due to pregnancy, and other high estrogen states, including use of estrogen replacement or birth control pills.

Total T3/Total Triiodothyronine

Triiodothyronine is the active thyroid hormone, and is also known as T3. Total T3 is typically elevated in hyperthyroidism, and lowered in hypothyroidism.

Free T3 / Free Triiodothyronine

Free T3 measures the free, unbound levels of triiodothyronine in your bloodstream. Free T3 is considered more accurate than Total T3. Free T3 is typically elevated in hyperthyroidism, and lowered in hypothyroidism.

T3 Resin Uptake (T3RU)

When done with a T3 and T4, the T3 resin uptake (T3RU) test is sometimes referred to as the T7 test. This test measures the amount of unsaturated binding sites on the transport (binding) hormones. Elevated T3RU is more commonly seen with hyperthyroidism.

Thyroglobulin/Tg

Thyroglobulin (Tg) levels are low or undetectable with normal thyroid function but can by elevated in thyroiditis, Gravesą disease, or thyroid cancer. Monitoring of Tg levels is frequently used to evaluate the effectiveness of treatment for thyroid cancer and to monitor for thyroid cancer recurrence.

Reverse T3

When the body is under stress, instead of converting T4 into T3 - the active form of thyroid hormone - the body conserves energy by making what is known as Reverse T3 (RT3), an inactive form of the T3 hormone. The value of RT3 tests in diagnosis is controversial, as some practitioners believe that the body continues to manufacture RT3 instead of active T3, causing various symptoms that are identified as the so-called "Wilson's syndrome."

RESOURCES:

Thyroid Blood Tests By Mary Shomon, About.com
Braverman, MD, Lewis E., and Robert D. Utiger, MD. Werner and Ingbar's The Thyroid: A Fundamental and Clinical Text. 9th ed., Philadelphia: Lippincott Williams & Wilkins (LWW), 2005.
Roti, Elio, et. al. "TSH Receptor Antibody Measurement in the Diagnosis and Management of Graves' Disease Is Rarely Necessary," The Journal of Clinical Endocrinology & Metabolism, Vol. 83, No. 11 3781-3784
http://jcem.endojournals.org/cgi/content/full/83/11/3781
Spencer, Carol. "Assay of Thyroid Hormones and Related Substances," Thyroid Manager. February 6, 2004.