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T4 Blood Test

Thyroxine, T4 Total, Tetraiodothyronine
Sample Report
Specimen Type: Blood


T4 Blood Test

A T4 test measures the amount of a particular hormone, T4 or Thyroxine, produced by the thyroid gland. T4, whose name comes from the fact that it contains 4 molecules of iodine, helps maintain the body's metabolism, temperature, and heart rate. Production of T4 is linked to the production of Thyroid Stimulating Hormone (TSH) by the pituitary gland. For this reason T4 and TSH are usually evaluated together. Irregular T4 levels may be caused by thyroid disorders such as hyperthyroidism or hypothyroidism.

Because most T4 in the body is bound to proteins, a person with irregular protein levels or protein binding issues may not have accurate results from a T4 test. In these cases a Free T4 test which measures unbound T4 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.

T4 can be ordered by itself but is often paired with a TSH test to evaluate thyroid function or help diagnose people who are experiencing symptoms associated with thyroid disorders. This test can also be useful for monitoring people who are being treated for a thyroid disorder. T4 is commonly ordered as part of a screening for women experiencing fertility issues.

Turnaround time for the T4 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 T4 test has no fasting requirements.



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