A T3 resin uptake (also called a T3 uptake or T3RU) is a blood test performed as part of an evaluation of thyroid function.
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.
The thyroid is a gland in the neck that produces the hormones that help regulate many body processes, including the following:
- 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.
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.
Some people have an inherited condition that involves high TBG levels despite normal thyroid function.
Lower-than-normal levels may indicate:
- Acute hepatitis (liver disease)
- Use of estrogen
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Higher-than-normal levels may indicate:
- Kidney failure
- Overactive thyroid (hyperthyroidism)
- Nephrotic syndrome
- Protein malnutrition
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