title: Diagnostic relevance of suppressed basal concentrations of TSH compared with the negative TRH test in detection and exclusion of hyperthyroidism.
abstract: To evaluate the sensitivity of basal TSH concentrations as determined by an "ultrasensitive" IRMA-assay (RIA-gnost h-TSH-monoclonal, Behring) versus a "negative" TRH test (defined as an increment of TSH less than or equal to 0.2 mU/l 20 min after administration of 400 micrograms TRH iv) in the diagnosis of hyperthyroidism we examined 193 consecutive patients from our thyroid outpatient clinic: 34 patients displayed hyperthyroidism (total T4: 184.4 +/- 26.0 mumol/l, effective thyroxine index: 1.25 +/- 0.08), whereas 12 had isolated T3-hyperthyroidism (total T3: 3.47 +/- 0.48 nmol/l). Employing the producer's definition of subnormal ("suppressed") bTSH concentrations (less than or equal to 0.1 mU/l), only 19 (41.3%) hyperthyroid patients would have been detected; on the other hand, one euthyroid patient would have been recognized false positively as hyperthyroid. Using the TRH test as criterion led to the correct diagnosis in 42 (sensitivity: 91.3%) hyperthyroid patients, whereas two had low bTSH concentrations (less than or equal to 0.5 mU/l), but a normal TSH response to TRH (greater than 2.0 mU/l). Raising the threshold concentration to 0.2 and, subsequently, to 0.4 mU TSH/l increased the number of correct results to 38 (sensitivity: 82.6%) and 43 (93.5%), respectively. This was associated with a concomitant decrease in specificity in the diagnosis of hyperthyroidism from 93.7 (0.1 mU/l) to 27.9% (0.4 mU/l). In conclusion, despite ultrasensitive methods for estimation of low TSH concentrations, the TRH test remains an irreplaceable tool for the correct diagnosis of hyperthyroidism.
authors.affiliation: I. Department of Internal Medicine, University of Vienna, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Roden
authors.forename: P
authors.initials: P
authors.lastname: Nowotny
authors.forename: H
authors.initials: H
authors.lastname: Vierhapper
authors.forename: W
authors.initials: W
authors.lastname: Waldhäusl
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000175:diagnosis*; D015592:Immunoradiometric Assay; D008297:Male; D008875:Middle Aged; D013972:Thyrotropin / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D013974:Thyroxine