Clinical Usefulness of the Growth Hormone–Releasing Peptide-2 Test for Hypothalamic-Pituitary Disorder

CONTEXT: Growth hormone deficiency (GHD) develops early in patients with hypothalamic-pituitary disorder and is frequently accompanied by other anterior pituitary hormone deficiencies, including secondary adrenal insufficiency (AI). A growth hormone–releasing peptide-2 (GHRP2) test, which is widely used for the diagnosis of patients with GHD, is thought to induce release of not only growth hormone (GH) but also ACTH. However, its clinical usefulness in hypothalamic-pituitary disorder is unclear. OBJECTIVE: We aimed to determine the clinical utility of the GHRP2 test in patients with hypothalamic-pituitary disorders, particularly for AI concomitant with GHD. METHODS: The GHRP2 test, a cosyntropin stimulation test, corticotropin-releasing hormone (CRH) tests, and/or insulin tolerance tests (ITTs) were performed on 36 patients with hypothalamic-pituitary disorder. RESULTS: Twenty-two (61%) had severe GHD, and 3 (8%) had moderate GHD by GHRP2. There was no difference in baseline ACTH and cortisol between non-GHD, moderate GHD, and severe GHD participants. However, a cosyntropin stimulation test and subsequent CRH tests and/or ITTs revealed that 17 (47%) had secondary AI and 16/17 (94%) cases of secondary AI were concomitant with severe GHD. ROC curve analysis demonstrated that the ACTH response in the GHRP2 test was useful for screening pituitary-AI, with a cutoff value of 1.55-fold (83% sensitivity and 88% specificity). Notably, the combination of ACTH response and the peak cortisol level in the GHRP2 test using each cutoff value (1.55-fold and 10 µg/dL, respectively) showed high specificity (100%) with high accuracy (0.94) for diagnosis of pituitary-AI. CONCLUSION: We recommend measuring ACTH as well as GH during the GHRP2 test to avoid overlooking or delaying diagnosis of secondary AI that frequently accompanies GHD.