The thyroid is the small, butterfly-shaped gland at the base of your neck that produces hormones to regulate the body's metabolism. When your thyroid hormone production drops (hypothyroidism), your body processes slow down and change, affecting essentially all the systems in your body.
You can measure your thyroid function with a thyroid blood test. Many labs only look only at thyroid-stimulating hormone (TSH) to assess thyroid health. Unfortunately, TSH alone offers only a narrow understanding of how your thyroid is working. It doesn't give a comprehensive picture of what's happening with your thyroid health or how to make specific improvements.
At Paloma Health, in addition to TSH, we believe it is critical to measure free triiodothyronine (fT3), free thyroxine (fT4), and TPO antibodies to fully understand what's happening with your thyroid health and how to make specific improvements. Each test offers a different piece of information to tailor a treatment plan for your particular needs.
What does a full thyroid panel include?
Thyroid stimulating hormone (TSH)
The pituitary gland produces thyroid-stimulating hormone (TSH) in the brain. The primary job of TSH is to regulate the amount of thyroid hormones—thyroxine (T4) and triiodothyronine (T3)—produced by the thyroid gland. This blood test measures how much overall thyroid-stimulating hormone is in your blood. While this is the standard test most doctors authorize, it won't provide detailed information on your thyroid activity. For instance, it may not show problems like your body not being able to use the available thyroid hormone.
Free T4 (fT4)
The thyroid produces two hormones: thyroxine (T4) and triiodothyronine (T3). T4 is primarily inactive. Its primary job as a "storage hormone" is to transport T3 to the proper organs in your body. T4 must be converted to T3 before your body can use it to get energy or deliver oxygen to cells. The T4 test helps determine the level of thyroid hormone in the body; however, it doesn't provide enough information by itself because it can be affected by the amount of protein in your blood.
Free T3 (fT3)
Triiodothyronine (T3) is the active version of the thyroid hormone. Thyroxine (T4) must convert into triiodothyronine (T3) before it becomes usable; this process happens primarily in the liver. T3 circulates in the bloodstream, both bound and not bound to protein. The free (unbound) T3 is what is able to enter and affect the body tissues. A total T3 test measures all the T3 in your body, even that which is unusable because it isn't bound to a protein. A free T3 a crucial test because it only measures the amount of free (unbound) T3 in your blood.
Testing for thyroid peroxidase (TPO) measures the levels of TPO antibodies in your blood. If you have high TPO levels, it may indicate Hashimoto's thyroiditis. Hashimoto's is an autoimmune condition in which your immune system attacks your thyroid as if it's a foreign invader. It's essential to include TPO antibodies in a complete thyroid test because you could have high TPO levels but still show normal TSH. Hashimoto's is the most common cause of hypothyroidism in the United States, and early detection may help slow its progression.
Reverse T3 is a byproduct of T4 metabolism. It is the inactive form of T3— meaning rT3 cannot carry out the same metabolic activities as T3. Reverse T3 may be an adaptive mechanism to benefit the body in certain situations where you don't want to have as much thyroid hormone activity at the tissue level. For example, if a patient is undergoing extreme stress, trauma, surgery, or malnutrition, rT3 may be a valuable marker.
A note from Paloma Health
Should your results indicate that your thyroid is underactive, it is treatable with thyroid hormone replacement medication. When choosing thyroid medication with your doctor, remember that there is no one-size-fits-all treatment. We recommend that you work with a trustworthy doctor who can assess your symptoms, history, and lab results to determine the best treatment plan for you.