The TSH assay is an in vitro test used for the quantitative determination of TSH in human serum and plasma. The anterior pituitary gland produces Thyroid Stimulating Hormone (TSH). Thyrotropin releasing hormone, which is produced by the hypothalamus, controls the production of TSH. TSH is also regulated by the Free T4, thyroxine, and T3, triiodothyronine, hormone levels in the blood. This is conducted via a negative feedback loop wherein the production of T4 is stimulated by TSH. In a euthyroid patient, an individual with a normal functioning thyroid, if T4 levels fall, then TSH levels should rise in response, triggering increased production of T4 by the thyroid gland.
If T4 levels are elevated, then TSH levels should decrease in order to lessen the stimulation of T4 production. This relationship between TSH and T4 is why TSH is often used to diagnose thyroid disease. Low levels of TSH may indicate hyperthyroidism, a condition where the thyroid overproduces thyroid hormones. This may also assist in the diagnosis of Graves’ disease, an autoimmune disease which results in hyperthyroidism. High levels of TSH may indicate hypothyroidism, a condition where the thyroid has decreased thyroid hormone production. This may also assist in the diagnosis of Hashimoto’s disease, an autoimmune disease in which the immune system ultimately destroys the thyroid gland, resulting in hypothyroidism.
While TSH is most commonly ordered to assess thyroid function, if thyroid disease is suspected and TSH levels are abnormal, then other thyroid testing may be analyzed in conjunction with TSH, including Free T4 and T3, Total T4 and T3, T3 Uptake, and autoantibodies like aTPO (anti-thyroid peroxidase antibody) and aTG (anti-thyroglobulin antibody).
At Solaris Diagnostics, TSH is measured with a third-generation immunoassay using monoclonal antibodies and chemiluminescent technology. Solaris diagnostics laboratory also test for other thyroid testing in conjunction with TSH, including FT4, FT3, Total T4, Total T3, T3 uptake, aTPO, and aTG and provide results in 24 hours from the time the sample is received in the laboratory.