TSH, Free T3, Free T4, Total T3, Reverse T3, TPO ab, Thyroglobulin ab
TSH (thyroid stimulating hormone) is the most common test used to evaluate thyroid function and symptoms related to a thyroid disorder such as hyperthyroidism, or hypothyroidism. Produced by the pituitary gland, the primary role of TSH in the body is to stabilize amounts of T4 (thyroxine) and T3 (triiodothyronine) in the blood. This process controls how much energy the body burns.
Free T3 (free triiodothyronine) is used to evaluate thyroid function and also in the assessment of abnormal binding protein disorders. Measurement of Free T3 is valuable in confirming the diagnosis of hyperthyroidism, when an elevated free or total thyroxine level is found. Abnormal total and free triiodothyronine concentrations may appear in T3 toxicosis, in the presence of normal thyroxine levels. The levels of free T3 are unaffected by carrier protein variation.
Free (Thyroxine) T4 can sometimes be indicated when binding globulin (TBG) problems are perceived, or when conventional test results appear inconsistent with clinical observations. It is common in subjects with high thyroxine-binding globulin hormone binding who are euthyroid (ie, free thyroxine should be normal in non-thyroidal diseases). It should appear normal in familial dysalbuminemic hyperthyroxinemia.
T3 Total (Triiodothyronine) is needed in patients who have clinical evidence for hyperthyroidism, in whom the usual thyroid profile result is reported as normal or borderline. The T3 Total test is recommended for patients with supraventricular tachycardia, for patients with fatigue and weight loss not otherwise explained, or for patients with proximal myopathy who also have T4 levels that are not elevated.
Reverse T3 is a biologically inactive form of T3. When T4 is converted to T3 in the body, a certain percentage of the T3 is in the form of RT3. When the body is under stress, thyroid hormone levels may be outside of normal ranges even though there is no thyroid disease present. RT3 may be elevated in non-thyroidal conditions, particularly the stress of illness.
Thyroid Peroxidase (TPO) Ab is used in the differential diagnosis of hypothyroidism and thyroiditis.
Thyroglobulin Ab is primarily used to detect and confirm autoimmune thyroiditis, Hashimoto thyroiditis.