Results: 7-10 Business Days
Description: Critical to your metabolism, thyroid function affects your energy level, heart rate, weight control, plus more.
This comprehensive evaluation of your thyroid hormone levels includes: Thyroid Panel w/TSH, Total T3, Reverse T3, Free T3, and Free T4
T-3 Uptake: A T3 resin uptake (also called a T3 uptake or T3RU) is performed as part of an evaluation of thyroid function. The thyroid is a gland in the neck that produces the hormones that help regulate many body processes, including growth, energy balance, body temperature, and heart rate. Thyroid function involves the interaction of many hormones, including triiodothyronine (T3) and thyroxine (T4). Both of these hormones exist in two forms in the blood. The more abundant forms are bound to a carrier protein called thyroxin-binding globulin (TBG), which helps transport the hormones through the body. The less abundant forms circulate unattached or “free.” Only the free forms of the thyroid hormones (free T4 and free T3) are available to affect body processes. The T3 resin uptake is used by doctors to estimate the amount of TBG in the blood, and how much T4 and T3 in the blood is free form and available to affect the body. If there’s either too much or too little TBG in the blood, the measurements of total T3 and T4 levels will be affected, which can make it difficult for doctors to tell whether a person actually has a thyroid problem without also knowing the results of the T3 resin uptake.
T4, total:A T4 test measures the blood level of the hormone T4, also known as thyroxine, which is produced by the thyroid gland and helps control metabolism and growth. The T4 test is performed as part of an evaluation of thyroid function. T4 measures the entire amount of thyroxine in the blood, including the amount attached to blood proteins that help transport the hormone through the bloodstream.
Free Thyroxine Index (T7): 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.
TSH (Thyroid Stimulating Hormone): The best way to initially test thyroid function is to measure the TSH level in a blood sample. A high TSH level indicates that the thyroid gland is failing because of a problem that is directly affecting the thyroid (primary hypothyroidism). The opposite situation, in which the TSH level is low, usually indicates that the person has an overactive thyroid that is producing too much thyroid hormone (hyperthyroidism). Occasionally, a low TSH may result from an abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the thyroid (secondary hypothyroidism). In most healthy individuals, a normal TSH value means that the thyroid is functioning normally.
T3, total triiodothryonine: Increased T3 often occurs in hyperthyroidism, but in approximately 5% of cases only T3 is elevated, “T3 toxicosis.” Do not confuse T3 with T3 uptake; these are two different tests. The latter is done very commonly as part of the usual thyroid profile. Less than 1% of T3 is unbound.
Reverse T3: Since thyroid hormone acts like our internal thermostat, thyroid hormones may be suppressed in times of stress. One way this is done is by converting the thyroid hormone T4 into an inactive form of the active T3 hormone called reverse T3. This lowers the amount of available active T3 which can lead to hypothyroid type symptoms.
Free T3: This test is used to evaluate thyroid function. It is primarily used to diagnose hyperthyroidism. It is also used to assess abnormal binding protein disorders and to monitor thyroid replacement and suppressive therapy.
Free T4: This test is used to evaluate thyroid function in individuals who may have protein abnormalities that could affect total T4 levels. It is used to evaluate thyroid function and monitor replacement and suppressive therapy.
Note: Result turn around times are an estimate and are not guaranteed. Our reference lab may need additional time due to weather, holidays, confirmation/repeat testing, or equipment maintenance.