• Julie Refardt, Cihan Atila, Irina Chifu, Emanuele Ferrante, Zoran Erlic, Juliana B Drummond, Rita Indirli, Roosmarijn C Drexhage, Clara O Sailer, Andrea Widmer, Susan Felder, Andrew S Powlson, Nina Hutter, Deborah R Vogt, Mark Gurnell, Beatriz S Soares, Johannes Hofland, Felix Beuschlein, Martin Fassnacht, Bettina Winzeler, and Mirjam Christ-Crain.
• From the Departments of Endocrinology, Diabetology, and Metabolism (J.R., C.A., C.O.S., A.W., S.F., N.H., B.W., M.C.-C.) and Clinical Research (J.R., C.A., C.O.S., A.W., S.F., N.H., D.R.V., B.W., M.C.-C.), University Hospital Basel, University of Basel, Basel, and the Department of Endocrinology, Diabetology, and Clinical Nutrition, University Hospital Zurich and University of Zurich (Z.E., F.B.), and the LOOP Zurich-Medical Research Center (F.B.), Zurich - all in Switzerland; the Department of Internal Medicine, Section of Endocrinology, Erasmus Medical Center, Rotterdam, the Netherlands (J.R., R.C.D., J.H.); the Division of Endocrinology and Diabetes, Department of Internal Medicine I, University Hospital, University of Würzburg (I.C., M.F.), and Central Laboratory, University Hospital Würzburg (M.F.), Würzburg, and Medizinische Klinik und Poliklinik IV, Klinikum der Universität, Ludwig Maximilians Universität München, Munich (F.B.) - all in Germany; the Endocrinology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico (E.F., R.I.), and the Department of Clinical Sciences and Community Health, University of Milan (R.I.) - both in Milan; the Department of Internal Medicine, Medical School of the Federal University of Minas Gerais, Belo Horizonte, Brazil (J.B.D., B.S.S.); and Wellcome-MRC Institute of Metabolic Science, University of Cambridge and Addenbrooke's Hospital, Cambridge Biomedical Campus (A.S.P., M.G.) and Cambridge NIHR Biomedical Research Centre, Cambridge University Hospitals (M.G.) - both in Cambridge, United Kingdom.
• N. Engl. J. Med. 2023 Nov 16; 389 (20): 187718871877-1887.

BackgroundDistinguishing between arginine vasopressin (AVP) deficiency and primary polydipsia is challenging. Hypertonic saline-stimulated copeptin has been used to diagnose AVP deficiency with high accuracy but requires close sodium monitoring. Arginine-stimulated copeptin has shown similar diagnostic accuracy but with a simpler test protocol. However, data are lacking from a head-to-head comparison between arginine-stimulated copeptin and hypertonic saline-stimulated copeptin in the diagnosis of AVP deficiency.MethodsIn this international, noninferiority trial, we assigned adult patients with polydipsia and hypotonic polyuria or a known diagnosis of AVP deficiency to undergo diagnostic evaluation with hypertonic-saline stimulation on one day and with arginine stimulation on another day. Two endocrinologists independently made the final diagnosis of AVP deficiency or primary polydipsia with use of clinical information, treatment response, and the hypertonic-saline test results. The primary outcome was the overall diagnostic accuracy according to prespecified copeptin cutoff values of 3.8 pmol per liter after 60 minutes for arginine and 4.9 pmol per liter once the sodium level was more than 149 mmol per liter for hypertonic saline.ResultsOf the 158 patients who underwent the two tests, 69 (44%) received the diagnosis of AVP deficiency and 89 (56%) received the diagnosis of primary polydipsia. The diagnostic accuracy was 74.4% (95% confidence interval [CI], 67.0 to 80.6) for arginine-stimulated copeptin and 95.6% (95% CI, 91.1 to 97.8) for hypertonic saline-stimulated copeptin (estimated difference, -21.2 percentage points; 95% CI, -28.7 to -14.3). Adverse events were generally mild with the two tests. A total of 72% of the patients preferred testing with arginine as compared with hypertonic saline. Arginine-stimulated copeptin at a value of 3.0 pmol per liter or less led to a diagnosis of AVP deficiency with a specificity of 90.9% (95% CI, 81.7 to 95.7), whereas levels of more than 5.2 pmol per liter led to a diagnosis of primary polydipsia with a specificity of 91.4% (95% CI, 83.7 to 95.6).ConclusionsAmong adult patients with polyuria polydipsia syndrome, AVP deficiency was more accurately diagnosed with hypertonic saline-stimulated copeptin than with arginine-stimulated copeptin. (Funded by the Swiss National Science Foundation; CARGOx ClinicalTrials.gov number, NCT03572166.).Copyright © 2023 Massachusetts Medical Society.

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