Thyroid function tests check for hyper- or hypothyroidism. Both are associated with a lack of energy. Interestingly, hyperthyroidism causes you to feel hyper before feeling fatigued.
TSH Level: The pituitary hormone called the “thyroid-stimulating hormone” (TSH) regulates the thyroid gland. TSH is one of the best indicators of how your thyroid gland is functioning. Hyperthyroidism usually results in a decreased TSH level. Hypothyroidism usually results in an elevated TSH level. Subclinical hyperthyroidism typically occurs when you have a low or borderline low TSH level and normal levels of triiodothyronine (T3) or thyroxine (T4). Subclinical hypothyroidism typically occurs when someone has a high or borderline high TSH level and normal T3 and T4 levels. This is more common in people over 60.
Free T4 Level: This is the less active hormone from the thyroid that’s converted to the more active T3 to regulate metabolism. Too much T4 leads to excessive energy and a profound feeling of the jitters. Also, weight loss. This is hyperthyroidism. Too little T4 leads to reduced energy and a profound feeling of the blahs—and of course weight gain.
WATCH VIDEO: How the Thyroid Works
Free T3 Level: This is the most active thyroid hormone. It regulates metabolism in much the same way as T4. Both of these hormones influence the pituitary’s secretion of TSH. If there’s too little T3 or T4 in circulation, TSH goes up. If there’s too much, the TSH goes down. This seesaw between pituitary hormone and active hormone of the gland is known as a feedback relationship.
Thyroglobulin and Thyroid Microsomal AB: These are autoantibodies to the thyroid gland. People make antibodies against their own thyroid, rather than an intruder bacteria or virus, which is what antibodies are designed to do. People who have thyroid autoantibodies and an elevated level of TSH progress to overt hypothyroidism at a rate of three to five percent per year. These are the most common thyroid autoantibodies seen in people with hypothyroidism.