The T3RU test measures the level of proteins that carry thyroid hormone in the blood. This can help your health care provider interpret the results of
Resin T3 uptake; T3 resin uptake; Thyroid hormone-binding ratio
How the test is performed
A blood sample is needed. For information on how this is done, see:
How to prepare for the test
Your health care provider will tell you, if needed, to stop taking drugs that may interfere with the test.
Drugs that can increase T3RU levels include:
Salicylates (high dose)
The following can increase thyroxin binding globulin (TBG) levels:
Male hormones (androgens)
Drugs that can decrease T3RU levels include:
Birth control pills
Pregnancy can also decrease T3RU levels.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is done to check your thyroid function. Thyroid function is complex and depends on the action of many different hormones, including thyroid-stimulating hormone (TSH), T3, and T4.
This test helps see how much thyroxin binding globulin (TBG) is available. TBG is a protein that carries most of the T3 and T4 in the blood.
The higher the level of TBG, the lower the level of T3RU. A higher T3RU level means less TBG is available. This may be caused by
Your doctor may order this test if you have signs of a thyroid disorder, including:
Normal values range from 24 – 37%.
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples.Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Higher-than-normal levels may indicate:
- Overactive thyroid (hyperthyroidism)
Nephrotic syndrome Protein malnutrition
Lower-than-normal levels may indicate:
- Underactive thyroid (
hypothyroidism, primary hypothyroidism, or secondary hypothyroidism)
- Use of estrogen
Abnormal results may also be due to an inherited condition of high TBG levels. Usually thyroid function is normal in people with this condition.
This test may also be done for:
Chronic thyroiditis (Hashimoto’s disease)
- Drug-induced hypothyroidism
Graves disease Subacute thyroiditis
- Thyrotoxic periodic paralysis
Toxic nodular goiter
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)