Context: The insulin tolerance test (ITT) is the current standard diagnostic test for the diagnosis of adult GH deficiency (GHD), but alternative tests, as the GHRH-arginine test has been proposed.

Objective: We investigated the sensitivity and specificity of the GHRH-arginine test using ITT as gold standard in diagnosing GHD in a group of young adults treated with cranial irradiation (CRT) for childhood ALL. We estimated the positive and negative predictive values of the GHRH-arginine test among patients, and a number of individual characteristics and therapy related factors during both the GHRH-arginine test and ITT.

Design: 43 young adults, treated for childhood ALL with 18-30 Gy of CRT and chemotherapy was studied and comparison was made with matched controls.

Results & Conclusions: We evaluated four different cut-off levels for GHD in the GHRH-arginine test; 5, 7.5, 9 and 16.5 µg/L. Using 7.5 µg/L as cut-off yielded high specificity (94%), but at the same time the sensitivity was only 66%, which leads to a low negative predictive value (27%). On the other hand, a failed GH response to the GHRH-arginine test accurately reflects the presence of radiation-induced GHD, illustrated by a high positive predictive value (95% at 7.5 µg/L). Only age at CRT and BMI remained significant predictors of the peak GH during the GHRH-arginine test. Since a high proportion of GHD patients show a normal response to the GHRH-arginine test, it cannot be used reliably to exclude GHD in these patients. Complementary ITT is also warranted to confirm GHD in obese patients.