Comparison of thyroid stimulating hormone and triiodothyronine response to thyrotrophin releasing hormone in the assessment of thyroid status.

The response to an intravenous dose of 200 microng of thyrotrophin releasing hormone (TRH) has been studied by estimating, by radioimmunoassay, baseline levels followed by further estimations of thyroid stimulating hormone (TSH) 20 minutes after the injection and triiodothyronine (T3) three hours after the injection in 112 patients referred for routine thyroid assessment. Comparison of diagnostic accuracy of the response to TRH gave similar results with both procedures but slightly better overall accuracy for the response measured by TSH assay. However, estimation of baseline T3 is a valuable test for hyperthyroidism, in contrast to baseline TSH, and combined with the estimation of T3 three hours after TRH injection provides an accurate additional test in borderline cases.