[Assessment of basal and stimulated TSH in overt and subclinical hyperthyroidism]

A TRH test was performed in 171 consecutive patients with a TSHbasal below the reference range. TSHbasal, TSHstimulated and delta TSH were determined and compared, using assays of the second and third generation. Free thyroid hormones were elevated in 48 and normal in 123 patients. The sensitivity of all evaluated parameters to assess overt hyperthyroidism was between 94 and 98% with both assays, using a defined TSH threshold (mean of patients with overt hyperthyroidism +2 standard deviations). However, specificity was much lower, only 34 and 23%, respectively, for the TSHbasal. Significant improvement followed TRH-testing: specificity rose to 63 and 57%. The superior reproducibility of TSH values in the lower range, using the third generation assays, was of little value in the differentiation between subclinical and overt hyperthyroidism.