Endocrine Abstracts

Introduction: Distinguishing arginine vasopressin deficiency (AVD) from primary polydipsia (PP) can be challenging in clinical practice. Copeptin is produced in equimolar amount to AV and is considered diagnostic biomarker to establish the diagnosis of AVD with and without provocative testing.

Methods: Patients referred with polydipsia, hypotonic polyuria (>3L/day) and normonatraemia had overnight fasting plasma copeptin measured. Those with level of <3 pmol/l underwent glucagon-stimulated copeptin test (GSC) to confirm AVD. Copeptin was measured at baseline, 30, 60, 90, 120, 150, and 180 minutes after administration of 1mg glucagon subcutaneously with peak level <4.6 pmol/l was considered diagnostic of AVD.

Results: Eight patients were referred to our centre, 6 (75%) were male, median age was 42 years (range 26-72). Four patients (50%) had overnight fasting copeptin above the diagnostic cut-off (>3 pmol/l) with a median level 7 pmol/l (range 4.6-9.4). These patients were diagnosed with PP and managed with reduction of fluid intake and careful monitoring of clinical and biochemical parameters. Three patients (38%) had low fasting copeptin and one couldn’t tolerate fluid abstinence. These patients underwent GSC. Results are shown in the table: The two patients diagnosed with AVD were treated successfully with desmopressin and had significant improvement in their symptoms. GSC test was tolerated easily by all patients with no adverse consequences reported.

Conclusion: Recent evaluations demonstrated high distinctive accuracy of measuring copeptin in the differential diagnosis of polyuria polydipsia syndrome. In our centre, we have replaced the water deprivation test with copeptin based tests due to reliability, tolerability, and precision. GSC can be utilised when there is inconclusive overnight fasting copeptin result or uncertainty.