[The negative TRH test: new differential assessment using a sensitive TSH assay].
Determination of TSH by the IRMA technique shows improved sensitivity and higher accuracy compared to TSH RIA, so that lower detection limits of 0.1 mU TSH/1 can be easily attained. Basal TSH values (bTSH) between 0.4 and 3.5 mU/l clearly define a euthyroid metabolic state. At a bTSH lower than 0.4 mU/l a TRH test should be performed to exclude latent or overt hyperthyroidism. Stimulated TSH values (sTSH) greater than 2.5 mU/l are considered to be a positive test which rules out hyperthyroidism. A negative TRH test (sTSH less than 2.5 mU/l), on the other hand, is an abnormal result which may have several causes and thus does not per se evidence a hyperthyroid state. In a group of thyroid inpatients, a differential new assessment of the so-called negative TRH test for the exclusion of hyperthyroidism was attempted in 355 patients with blunted TSH response (sTSH less than 2.5 mU/l) by means of a methodologically improved TSH assay (IRMA principle). In overt hyperthyroidism the bTSH was lower than 0.1 mU/l in 42 out of 44 cases (95%); sTSH was in all cases below 0.5 mU/l (100%). 78% of the clinically euthyroid patients had a blunted bTSH (0.1-0.4 mU/l) and a significant (p less than 0.001) increase of sTSH up to 0.5-2.5 mU/l. Excluding the patients treated with L-thyroxine, 147 cases had sTSH less than 2.5 mU/l. Among the 65 patients with sTSH ranging between 0.5 and 2.5 mU/l, 66% were euthyroid and 34% borderline cases from a clinical point of view (mostly compensated autonomous adenomas), but there were no hyperthyroid cases.(ABSTRACT TRUNCATED AT 250 WORDS)
D003937:Diagnosis, Differential; D003951:Diagnostic Errors; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood; D007158:Immunologic Techniques; D011863:Radioimmunoassay; D013959:Thyroid Diseases / Q000097:blood*; D013972:Thyrotropin / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone
D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin
Negativer TRH-Test: Differenzierte Neubewertung durch empfindliche TSH-Bestimmung.