Measurement of thyroid-stimulating hormone from blood serum is regarded as the most important test for early detection of hyperthyroidism and hypothyroidism, and is one of the thyroid function tests used to diagnose and treat thyroid disease. The result of this assay is suggestive of the presence and cause of thyroid disease, since a measurement of elevated TSH generally indicates hypothyroidism, while a measurement of low TSH generally indicates hyperthyroidism. However, when TSH is measured by itself, it can yield misleading results, so additional thyroid function tests must be compared with the result of this test for accurate diagnosis.
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History
First-generation TSH assays were done by radioimmunoassay and were introduced in 1965. There were variations and improvements upon TSH radioimmunoassay, but their use declined as a new immunometric assay technique became available in the middle of the 1980s. The new techniques were more accurate, leading to the second, third, and even fourth generations of TSH assay, with each generation possessing ten times greater functional sensitivity than the last. Third generation immunometric assay methods are typically automated. Fourth generation TSH immunometric assay has been developed for use in research.
Current status
Third generation TSH assay is the current requirement for modern standards of care. At present, TSH testing in the United States is typically carried out with automated platforms using advanced forms of immunometric assay. Nonetheless, there is currently no international standard for measurement of thyroid-stimulating hormone.
Interpretation
Accurate interpretation takes a variety of factors into account, such as the thyroid hormones i.e. thyroxine (T4) and triiodothyronine (T3), current medical status (such as pregnancy), certain medications like propylthiouracil, temporal effects including circadian rhythm and hysteresis, and other past medical history.