SUN-297 Development of a Local Reference Range for Hypertonic Saline-Stimulated Copeptin

Differentiating between primary polydipsia and central diabetes insipidus (DI) can be challenging. The water deprivation test has traditionally been used to diagnosis DI, however has poor diagnostic accuracy (1). Direct measurement of anti-diuretic hormone (ADH) is limited clinically. Copeptin is the C-terminal glycoprotein moiety of ADH prohormone, and correlates well with plasma ADH. Unlike ADH, copeptin is easy to measure (2). Hypertonic saline stimulated copeptin measurements have recently been described for the diagnosis of central DI. A copeptin cut-off of >4.9 pmol/L has a diagnostic accuracy of 96.5% for distinguishing primary polydipsia from central DI (3). A copeptin assay has recently been established in our laboratory. Validation of hypertonic saline-stimulated copeptin concentrations in our local population is needed before this test can be used with confidence in patients presenting to our institution with polyuria-polydipsia syndrome. The aim of this study was to develop a local reference range for hypertonic saline-stimulated copeptin in healthy volunteers. Twenty healthy volunteers (10 male and 10 female) were recruited. Subjects underwent a hypertonic saline test, as previously described (3). Hypertonic saline (3%) was administered as an initial 250 mL bolus followed by 0.15 mL/kg/minute until a target serum sodium of ≥150 mmol/L was reached. At this time, blood was drawn for copeptin. Twelve healthy volunteers (7 females; 5 males) have undergone the study to date. Median age was 28 years (range 26-50); median body weight 75.7 kg (range 57.9 -94.5); median baseline plasma sodium 138 mmol/L (range 136 - 140) and median serum osmolality 289.5 (range 281-297). Median peak sodium was 152 mmol/L (range 150-154) with osmolality 314.5 mmol/kg (range 306-320). Median volume of hypertonic saline infused was 1583 mL (1230-2177) and median hypertonic saline stimulated copeptin was 29.2 pmol/L (9.6-167.4). Overall symptom burden was 5/10 (range 3/10-9/10). There were no serious adverse events. Development of a local reference range for hypertonic saline stimulated copeptin measurements will assist in interpretation of the test in our local population of patients presenting with polyuria-polydipsia syndrome. References 1. Fenske W, Quinkler M, Lorenz D, Zopf K, Haagen U, Papassotiriou et al. Copeptin in the differential diagnosis of the polyuria-polydipsia syndrome- revisiting the direct and indirect water deprivation tests. JCEM. 2011;96:1506-1515 2. Timper K, Fenske W, Kuhn F, Frech N, Arici B, Rutishauser J et al. Diagnostic accuracy of copeptin in the differential diagnosis of the polyuria-polydipsia syndrome: a prospective multicenter study. JCEM. 2015;100:2268-2274 3. Fenske, W, Refardt J, Chifu I, Schnyder I, Winzeler B, Drummond J. A copeptin-based approach in the diagnosis of diabetes insipidus. NEJM. 2018;379:428-439