Similar to tests in the clinic, at-home thyroid tests analyze your blood for levels of a myriad of vital signs. Thyroid hormone (TSH) is the hormone most commonly measured by thyroid tests, although it is not a hormone secreted by the thyroid gland.
Instead, TSH is produced by the pituitary gland and leads to the production of T3 and T4. TSH levels usually rise when T3 and T4 levels are low, indicating that the body needs to produce more of these hormones (or vice versa). While affordable thyroid tests only look at TSH, this biomarker does not provide a complete picture of thyroid function.
Looking at the TSH only assumes that the body is functioning normally and that there are no other issues at play, which is an oversimplification of the physical process. In fact, a Study 20182 I found that screening for thyroid problems with a TSH test can miss hypothyroidism. Therefore, a normal TSH level does not guarantee that the thyroid gland is functioning normally.
The most comprehensive view of thyroid function includes direct tests for T3 and T4 levels, as well as thyroid antibodies and Reverse T3 or rT3. As mentioned earlier, the first two are hormones that are produced directly by the thyroid gland. When testing, you can look at your total hormone levels or free levels written in FT3 and FT4 or free T3 and T4. These “free” hormones are not bound to thyroxine-binding globulin, and highly sensitive assays are best for disease recognition.
While most of the tests on our list look at the FT3 and FT4, only a handful keep an eye on the rT3 test. When the body converts T4 to T3, it creates rT3, or an inactive form of T3 in specific proportions. Sometimes, the body may be prevented from making T3, rather than overproducing it. This metabolite acts like a brake on thyroid function, slowing down the metabolism. As a result, it begins with many of the same symptoms of hypothyroidism, including weight gain. both disease and chronic anxiety3 They have been linked to high levels of rT3 – which means it’s another important test to consider when making your choice.