Esben Søndergaard

Background The diagnosis of the polyuria–polydipsia syndrome is challenging. Copeptin is a robust biomarker of arginine vasopressin (AVP) secretion. Arginine, which stimulates growth hormone (GH), has been shown also to stimulate copeptin secretion via unknown mechanisms. Aim The aim was to investigate copeptin levels in response to three different GH stimulation tests in patients suspected of GH deficiency. Methods In this cross-sectional study, we measured plasma copeptin levels at baseline and at 60, 105, and 150 min in patients undergoing a stimulation test for growth hormone deficiency with either arginine ( n = 16), clonidine ( n = 8) or the insulin tolerance test (ITT) ( n = 10). Results In patients undergoing the arginine test, the mean age was 9 years, and 10 years for clonidine. The ITT was only performed in adult patients (>18 years) with a mean age of 49 years. Copeptin level increased significantly from baseline to 60 min after arginine ( P < 0.01) and ITT ( P < 0.01). By contrast, copeptin level tended to decrease after clonidine stimulation ( P = 0.14). Conclusion These data support that infusion of arginine increases plasma copeptin levels and reveal a comparable response after an ITT. We hypothesize that the underlying mechanism is abrogation of somatostatin-induced AVP suppression.