Hypertonic saline test: a salty journey from a

August Palma; James MacFarlane; Chris Hallet-Morley; Danilo Inchiappa; Katrina Lezaron; Sue Parsons; Denise Tapa; Ruth Ronneberger; Andrew Powlson; Mark Gurnell

doi:10.1530/endoabs.117.P184

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Endocrine Abstracts (2026) 117 P184 | DOI: 10.1530/endoabs.117.P184

SFEBES2026 Poster Presentations Neuroendocrinology and Pituitary (40 abstracts)

Hypertonic saline test: a salty journey from a ‘feared’ procedure to a safe, effective diagnostic for arginine vasopressin deficiency

August Palma ¹ , James MacFarlane ¹ , Chris Hallet-Morley ¹ , Danilo Inchiappa ¹ , Katrina Lezaron ¹ , Sue Parsons ¹ , Denise Tapa ¹ , Ruth Ronneberger ¹ , Andrew Powlson ¹ & Mark Gurnell ^1,2

Author affiliations

¹Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom; ²University of Cambridge, Cambridge, United Kingdom

Background: Distinguishing arginine vasopressin deficiency (AVP-D) or resistance (AVP-R) from primary polydipsia (PP) is clinically challenging. The water deprivation test (WDT) is widely used but is labour-intensive, time-consuming, and yields a higher rate of equivocal results. The hypertonic saline-stimulated copeptin test (HST) offers greater diagnostic accuracy in differentiating AVP-D from PP. We describe the establishment of HST as routine care in our endocrine centre, addressing concerns about safety and feasibility.

Methods: Discussions were held at monthly endocrine service meetings before adoption. A consultant endocrinologist and specialist nurse co-developed a clinical protocol and patient information leaflet. Initially, one test per month was carried out, later increasing to two per month. Patients underwent HST as outpatients, with monitoring of symptoms and serum sodium before, during and after stimulation. Technical success was predefined as post-stimulation sodium >149 mmol/l. Copeptin levels determined diagnostic category (complete AVP-D, partial AVP-D, PP, or AVP-R).

Results: Twenty-six patients (19 women, 7 men; median age 43 years) were studied. All achieved technical success (100%) with post-stimulation sodium >149 mmol/l. No complications were reported; all patients were discharged the same day with normal sodium levels. Mild to moderate transient symptoms were documented but resolved. Diagnoses: 3 (11.5 %) complete AVP-D, 2 (7.7 %) partial AVP-D, 20 (76.9 %) PP, and 1 (3.8 %) AVP-R based on baseline copeptin.

Conclusion: Implementation of HST as an outpatient diagnostic is feasible and safe when adequate protocols, personnel training, and monitoring are in place. The 100 % technical success rate, absence of complications, and clear diagnostic outcomes support HST as a highly efficient alternative to WDT. We propose copeptin stimulation tests be considered part of the standard approach for the evaluation of hypotonic polyuria, when basal laboratory tests are indeterminate.