Comparison between TRH-stimulated TSH and basal TSH measurement by a commercial immunoradiometric assay in the management of thyroid disease

摘要

In order to assess the current diagnostic role of the TRH test following the introduction of more sensitive "second generation" TSH assays, we studied a series of 259 outpatients, 237 women and 22 men, mean age 44.7 years (range 12-82), 91 of whom (35%) with untreated simple goiter, 133 (51%) with simple nodular goiter on steady state L-thyroxine treatment, 18 (7%) with overt or subclinical hyper-thyroidism and 17 (7%) with overt or subclinical hypothyroidism, compared to a control group of 26 euthyroid healthy subjects. Serum TSH was measured by a commercial immunoradiometric assay (clinical sensitivity 0.1 μU/ml). TSH response to TRH was evaluated 30 minutes after giving 200 μg TRH i.v. bolus, the results being analyzed both as absolute increase (Δ-TSH=stimulated TSH minus basal TSH) and as relative increase (R-TSH=stimulated TSH/basal TSH). Using cut-off values of 0.3-3.2 μU/ml, basal TSH measurement was able to detect hypothyroidism (specificity =100%) and to exclude hyperthyroidism (sensivity=96.9%), but failed to accurately prove hyperthyroidism (specificity= 93.4%) and, above all, to exclude hypothyroidism (sensitivity=35.3%) in our ambulatory patients. The Δ-TSH values showed a basal TSH-dependent linear increase (r=+0.87, p<0.001) both including only patients (n=139) with basal TSH level in the euthyr-oidism range and including all patients (n=223) having TSH responsive to TRH.