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T3 Blood Test

T3 Total, Triiodothyronine (T3)
Sample Report
Specimen Type: Blood


T3 Blood Test

A T3 test measures T3 or Triiodothyronine, a particular hormone produced by the thyroid gland. T3, whose name comes from the fact that it contains 3 molecules of iodine, is a hormone which helps control the body's metabolism, temperature, and heart rate. Production of T3 is linked to the production of Thyroid Stimulating Hormone (TSH) by the pituitary gland.  T4, another hormone produced by the thyroid gland, is often converted into T3 in the liver and other body tissues. Irregular T3 levels may be caused by thyroid disorders such as hyperthyroidism or hypothyroidism. A T3 test is often ordered along with a T4 and/or a TSH test.

Because most T3 in the body is bound to proteins, a person with irregular protein levels or protein binding issues may not have accurate results from a T3 test. In these cases a Free T3 test which measures unbound T3 may be more effective.

Common symptoms of thyroid disorders include but are not limited to anxiety, irregular weight gain or loss, insomnia, diarrhea, constipation, irritation or sensitivity in the eyes, increased heart rate, dry skin, hair loss, and menstrual irregularity in women.

A T3 test is typically ordered to evaluate thyroid function or when someone is experiencing symptoms associated with thyroid disorders. This test is most commonly ordered when someone has had irregular results from a TSH or T4 test.

Turnaround time for the T3 test is typically 1 business day.

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.


This T3 test has no fasting requirements.



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