Thyroid Blood Tests
TSH Test
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.
As of 2003, the American Association of Clinical Endocrinologists is recommending that the normal range run from 0.3 to
3.0, versus the older range of 0.5 to 5.5.
So, according to the new standards, levels above 3.0 are evidence of possible hypothyroidism, and levels below 0.3 are
evidence of possible hyperthyroidism. Keep in mind that there is disagreement among practitioners, and some follow the older
range, others use the newer range.
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/Serum 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.
******************************************************************************************