Context: The GHRH plus arginine (GHRH+Arg) test is a promising alternative to the insulin tolerance test (ITT) for diagnosis of adult GH deficiency (AGHD).
Objectives: The objectives of the study were to validate the GHRH+Arg test for diagnosis of AGHD, using the ITT as comparator and a GH assay calibrated according to recent international recommendations, and to study the repeatability and tolerance of both tests.
Design: This was a multicenter, randomized, open-label, phase III study.
Setting: The study was conducted at 10 French university hospitals.
Subjects: Sixty-nine subjects (38 and 15 with high and low probability of GH deficiency, respectively, and 16 healthy controls) were randomized: 35 to the GHRH+Arg-GHRH+Arg-ITT test sequence and 34 to the ITT-ITT-GHRH+Arg test sequence.
Interventions: Each subject underwent three tests of GH secretion separated by 24 h or more.
Main outcome measures: The primary variable used for response assessments was serum peak GH response. Test results were compared with the final AGHD diagnosis.
Results: Peak GH responses in the two tests were strongly correlated. A cutoff value of 7.89 microg/liter for GHRH+Arg corresponding to 3 microg/liter for ITT was calculated. The cutoff value leading to 95% specificity with the GHRH+Arg test was measured at about 3.67 microg/liter (sensitivity 79.0%). Intermethod agreement and repeatability were high. Both tests were well tolerated. A preference for the GHRH+Arg test was expressed by 74% of subjects.
Conclusions: The GHRH+Arg test demonstrated good accuracy and repeatability, was at least as sensitive as the ITT, and was associated with better subject acceptability. The GHRH+Arg test represents a good alternative to the ITT for the diagnosis of AGHD.