What is a thyroid test?

The thyroid gland, which is in the front of the neck, secretes thyroid hormones (such as, thyroxine [T4] and triiodothyronine [T3]) that help regulate critical bodily functions like metabolism and maintaining body temperature. When doctors notice problems in these or other dependent parameters, they recommend testing the thyroid gland's function. Testing evaluates how well the thyroid gland is working by measuring the amount of thyroid hormones in the bloodstream.

Why do you need a thyroid profile test?

The thyroid blood test is used to assess thyroid gland function. If the thyroid gland is malfunctioning, a person can either have hypothyroidism (an underactive thyroid) or hyperthyroidism (an overactive thyroid). The panel can help in the diagnosis of disrupted thyroid function and thyroid disorders by measuring thyroid hormone levels in the blood.

A thyroid panel may also be used to monitor hyperthyroidism treatment, and evaluate those getting thyroid hormone replacement therapy. Depending on the test result, the medication dosage can then be altered or stopped altogether.

Testing involves taking a blood sample from a vein in your arm to test the amount of:

TSH (Thyroid-stimulating hormone)
T4
T3
Free T3 and T4

How do you interpret thyroid test results?

The volume of each thyroid hormone in your bloodstream will be listed in your results. Test reports usually specify the standard reference ranges, and whether your hormone levels are within the normal range or not.

The thyroid hormone reference ranges vary depending on your health status, age, and the laboratory performing the testing. The following are the reference ranges established by the American Board of Internal Medicine for each component of the thyroid test:

TSH (Thyroid-stimulating hormone): ranges from 0.5 to 4 mIU/L
Free T4: ranges from 0.8 to 1.8 ng/dL
T3 total: ranges from 80 to 180 ng/dL

What happens during a thyroid test?

A blood sample for the thyroid test will be taken by a medical professional in a doctor's office or lab by putting a needle into a vein in the arm. They may apply a tourniquet around your upper arm, and then clean the needle puncture area properly before drawing blood. After the blood draw, the lab technician should apply a cotton swab or bandage stop the bleeding.