Rationalising the use of hypertonic saline-stimulated copeptin measurements in differentiating between AVP deficiency and primary polydipsia

Christos Barmpoudis; Ghaith Khaleel; Chris Boot; Andy James; Simon Pearce; Richard Quinton; Petros Perros; Anna Mitchell; Catherine Napier; Kerri Devine; Owain Leng; Yaasir Mamoojee

doi:10.1530/endoabs.117.OC2.5

OC2.5

Prev Next

Section Contents Cite

Endocrine Abstracts (2026) 117 OC2.5 | DOI: 10.1530/endoabs.117.OC2.5

SFEBES2026 Oral Communications Mechanisms and Management of Endocrine Disease (5 abstracts)

Rationalising the use of hypertonic saline-stimulated copeptin measurements in differentiating between AVP deficiency and primary polydipsia

Christos Barmpoudis , Ghaith Khaleel , Chris Boot , Andy James , Simon Pearce , Richard Quinton , Petros Perros , Anna Mitchell , Catherine Napier , Kerri Devine , Owain Leng & Yaasir Mamoojee

Author affiliations

Department of Endocrinology, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom

Polyuria-polydipsia syndrome, a relatively uncommon primary presentation to Endocrine services, is characterised by production of large volume of hypotonic urine. After excluding hyperglycaemia, hypercalcaemia, hypokalaemia and arginine-vasopressin resistance (diagnosed with elevated untimed serum copeptin levels), the main differentials are arginine-vasopressin deficiency (AVP-D) and primary polydipsia (PP). Hypertonic saline-stimulated copeptin (HSC) has emerged as the gold standard test to accurately differentiate between AVP-D and PP. HSC nevertheless requires intense monitoring, is not widely accessible and can predispose to seizures and thrombophlebitis. We reviewed our use of HSC from 2017 to 2020. AVP-D was excluded in 10 patients (defined as serum copeptin >4.9 pmol/L with concurrent serum sodium ≥150 mmol/L during HSC). In half of them, HSC was not necessary as AVP-D were ruled out by: 24hour urine output <2.5L(N=2), fasted urine osmolality >700 mOsm/kg(N=2) or hyponatraemia on random testing(N=1). We therefore devised a diagnostic algorithm sequentially incorporating untimed serum/urine biochemistry and paired serum/urine fasted biochemistry after 2 days of fluid restriction (2L daily), with 24hour urine collection on day 2, in patients with a high pre-test probability of PP. Our re-audit data (2021 to 2024 period) reveals that the need for HSC was eliminated in six out of eight patients with PP. For the two patients who underwent HSC, one had Wolfram syndrome and declined fluid restriction for 2 days and the other patient requested further confirmatory testing despite evidence of PP on paired urine/serum fasted biochemistry after 2 days of fluid restriction. Our diagnostic algorithm to sequentially investigate patients with a high pre-test probability of PP can eliminate the need for HSC in at least 75% of cases, making it a more favourable and widely accessible approach.