Endocrine Abstracts

Background: The spectrum of polyuria-polydipsia syndrome (PPS) includes diabetes insipidus (central or nephrogenic) and primary polydipsia. In clinical practice the differential diagnosis particularly of central diabetes insipidus (cDI) and primary polydipsia (PP) is often difficult. The current gold standard – the water deprivation test (WDT) with or without vasopressin (AVP) measurements – lacks reliable diagnostic accuracy. Arginine infusion is known to stimulate various hormones secreted by the anterior pituitary gland such as growth hormone and prolactin. Based on own preliminary data we hypothesized that arginine also stimulates AVP mirrored by copeptin, the C-terminal part of the precursor peptide. The aim of this study was to evaluate the diagnostic utility of copeptin measurements after arginine infusion in patients with PPS.

Methods: Between 2013 and 2017 patients with polyuria-polydipsia syndrome were included in this prospective study. Patients underwent first a standard water deprivation test for diagnosis of PP or cDI and second an arginine infusion (L-Arginine Hydrochloride 0.5 g/kg body weight i.v. over 30 min). Blood was withdrawn at different time points (e.g. 30, 45, 60 min) after arginine infusion for copeptin measurements. Additionally, 20 healthy controls underwent arginine infusion without prior WDT.

Results: A total of 51 patients (63% female) were enrolled. 28 (55%) patients were diagnosed with PP, 11 (22%) with complete DI and 12 (23%) with partial DI. The study was terminated in January 2017. Final results of copeptin levels will be measured in batch analysis in February 2017 and compared between patients with complete cDI, partial cDI and PP as well as 20 healthy volunteers. We would be delighted to present the final results of this study at the 19th European Congress of Endocrinology.

Significance: If our hypothesis is true, copeptin measurements after arginine infusion are a promising new tool in the differential diagnosis of polyuria–polydipsia syndrome with the advantage of short and safe test protocol.