Thyroid Panel

How is a thyroid panel used?

A thyroid panel is used to screen for or help diagnose hypo- and hyperthyroidism due to various thyroid disorders.

The preferred test to screen for thyroid disorders is a TSH test. If your TSH level is abnormal, it will usually be followed up with a test for total T4 or free T4. Sometimes a total T3 or free T3 will also be performed. Often, the laboratory will do this follow-up testing automatically, and this is known as reflex testing.  This saves your doctor time from having to wait for the results of the initial test and then requesting the additional testing to confirm or clarify a diagnosis.  Follow-up tests are often performed on the original sample that was submitted when the initial test was requested. A thyroid panel may be requested by your doctor to have all three tests performed at the same time to get a more complete picture.

When is it ordered?

A thyroid panel may be ordered as part of a health checkup or when symptoms suggest hypo- or hyperthyroidism due to a condition affecting the thyroid.

Signs and symptoms of hypothyroidism may include weight gain, dry skin, constipation, cold intolerance, puffy skin, hair loss, fatigue, and menstrual irregularity in women.

Signs and symptoms of hyperthyroidism may include increased heart rate, anxiety, weight loss, difficulty sleeping, tremors in the hands, weakness, and sometimes diarrhea. There may be puffiness around the eyes, dryness, irritation, and, in some cases, bulging of the eyes.

What do the test results mean?

If the feedback system involving the thyroid gland is not functioning properly due to one of a variety of disorders, then increased or decreased amounts of thyroid hormones may result. When TSH concentrations are increased, the thyroid will make and release inappropriate amounts of T4 and T3, and the patient may experience symptoms associated with hyperthyroidism. If there is decreased production of thyroid hormones, the patient may experience symptoms of hypothyroidism.

The following table summarizes test results and their potential meaning.

TSH	T4	T3	Interpetation
High	Normal	Normal	Mild (subclinical) hypothyroidism
High	Low	Low or normal	Hypthyroidism
Low	Normal	Normal	Mild (subclinical) hyperthyroidism
Low	High or normal	High or normal	Hyperthyroidism
Low	Low or normal	Low or normal	Nonthyroidal illness; rare pituitary (secondary) hypothyroidism

Is there anything else I should know?

In the past, panels of tests were more common.  More recently, however, the practice is to order, where possible, one initial or screening test and then follow up with additional testing, if needed, to reduce the number of unnecessary tests. With thyroid testing, one strategy is to screen with a TSH test and, if the results are abnormal, then order additional tests.  Many laboratories still perform thyroid panels, but this will become less common in the future as better screening strategies are developed.