The insulin tolerance test (ITT) is considered the gold standard for the diagnosis of adrenal insufficiency (AI). However, the test is unpleasant to perform and has the risk of serious complications. We therefore evaluated the clinical applicability of GHRP6, which is a known activator of the hypothalamic-pituitary-adrenal (HPA) axis, to test for AI. For this purpose a comparative clinical study was designed.
Forty-nine patients with suspected dysfunction of the HPA axis and 20 healthy controls were enrolled. The ITT was performed in patients, and GHRP6 (1 μg/kg) testing in patients and controls. Serum cortisol over 90 min after GHRP6, in comparison to the ITT, was the main outcome measure.
Thirty-one patients had a peak cortisol response of less than 500 nmol/l during ITT and were considered adrenal insufficient. For GHRP6, the mean cortisol peak was 227±25.7 nmol/l in the AI group versus 395±35.3 nmol/l in the adrenal sufficient (AS) group. ROC analysis of peak cortisol levels during GHRP6 test suggested an optimal threshold of 299 nmol/l for the diagnosis of AI (Sens. 71.0%, Spec. 77.8%). Applying upper (416 nmol/l) and lower (137 nmol/l) thresholds with high specificities in combination with early morning cortisol established the diagnosis in nearly half of the patients, even when the GHRP6 test is limited to 30 min duration. GHRP6 led to significant activation of the HPA axis with no detectable side effects, but had limited accuracy in comparison to the ITT.
growth hormone secretagogues - ghrelin - insulin tolerance test