The thyroid is a small, butterfly-shaped gland in the lower front of your neck. It is part of the endocrine system and secretes thyroxine (T4) and triiodothyronine (T3) hormones, necessary for regulating all the cells and tissues in your body. If your health care provider has recommended getting your thyroid level checked, this guide will explain what the standard blood tests are used for and what they can tell you about your health.

What Do Thyroid Tests Check?

If you’ve been experiencing unexplained weight gain or weight loss, depression or anxiety, fatigue, poor concentration, and heat or cold intolerance, your health care provider may recommend thyroid function tests. These blood tests measure thyroid hormones and other substances that regulate thyroid function and determine if you might have hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), or detect any tumors or other disorders that may be causing problems.  

What Are the Main Thyroid Tests?

TSH

The pituitary gland produces thyroid stimulating hormone (TSH), which regulates how much T3 and T4 are produced by the thyroid gland. If your TSH levels come back too high or too low—above 4.0 or below 0.5 milli-international units of hormone per liter of blood (mIU/L)—it’s often an indicator that the thyroid gland isn’t working correctly. High TSH levels point to hypothyroidism, but if levels are too low, it could be an indicator of hyperthyroidism.

T4

Thyroxine is the main form of thyroid hormone. The T4 blood test measures the total amount of thyroxine circulating in the blood and the free T4—the active thyroxine not bonded to transport proteins so that it can enter and affect body tissues.  

Normal TSH and T4 tests indicate a normally functioning thyroid gland, while an elevated TSH and low free T4 reading indicate primary hypothyroidism due to a thyroid gland disease. Low TSH and low free T4 test suggest secondary hypothyroidism due to either a pituitary gland or hypothalamus disease. Low TSH and high T4 levels are generally always present in someone who has hyperthyroidism. 

T3

Usually, this test is ordered if T4 and TSH results suggest hyperthyroidism, or you are exhibiting symptoms—like unintentional weight loss, rapid or irregular heartbeat, nervousness, and irritability—of an overactive thyroid. It measures the total T3, free T3, and reverse T3—the inactive mirror image of T3. Abnormally high levels indicate Graves’ disease—an autoimmune disorder that causes an overproduction of thyroid hormones.

When you need thyroid function testing done, trust the professionals at My Blooming Health Lab. Since 2013, this privately-owned CLIA-waived company has provided efficient mobile laboratory testing to the St. Louis, MO, region. Their team has a combined average of 10 years of phlebotomy experience and is equipped with a Laboratory Information System to provide an exceptionally fast turnaround for test results. Visit their website and call them at (314) 942-3272 to learn more about their services.