[Comparison of 100 micrograms TRH intravenously and 40 mg TRH orally in euthyroidism (author's transl)].

Euthyroid in-patients were investigated with 100 micrograms TRH given intravenously and with 40 mg TRH given orally in order to compare the sensitivity of intravenous and oral TRH-test. In all patients (age 15-91 years) maximal TSH-levels 180 min after 40 mg TRH are significantly (p less than 0.01) higher than maximal TSH-levels 30 min after 100 micrograms TRH. In patients under 50 years of age TSH-30 and TSH-180 are identical on average (6.42 +/- 0.29 microunits/ml vs. 6.53 +/- 0.54 microunits/ml/log x +/- SDlog). In patients older than 50 years TSH-30 is significantly lower (p less than 0.02) than in patients aging less than 50 years (2.11 +/- 0.88 microunits/ml vs. 6.42 +/- 0.29 microunits/ml). Both age-related groups demonstrate no significant difference (p greater than 0.2) in TSH-180 after 40 mg TRH (6.53 +/- 0.54 microunits/ml vs. 3.65 +/- 0.74 microunits/ml). 14 cases (34%) are low or non responders to 100 micrograms TRH intravenously, 8 (19.5%) only following 40 mg TRH orally. Patients with complete TSH-suppression (both iv. and oral TRH-test negative) show significant (p less than 0.05) higher ETR, T4 and fT4 than patients with partial TSH-suppression (iv. negative and oral TRH-test positive). The dose of 100 micrograms TRH does not increase the sensitivity of the test, the specificity is decreased in older patients, the dose of 100 micrograms TRH seems to be to low to yield reliable results. 40 mg TRH orally does not show any false positive findings, because TSH-stimulation is longer and more intensive. T3 increase three hours after orally TRH-application indicates an intact feedback mechanism.