Exogenous TRH, given intravenously in a pharmacological dose of 200ΓÇô400┬╡g, induces a rise in TSH which peaks approximately twenty minutes later and then declines, but not to basal levels, by sixty minutes in normal subjects. The peak TSH response to TRH is proportional to basal TSH, and with current TSH assays, provides little added information in most cases. In hypothyroid subjects, the basal TSH is elevated and the TSH response is exaggerated. It is seldom necessary, however, to perform a TRH test in the diagnosis of hypothyroidism.
