Nicole Nigro1,2, Bettina Winzeler1,2, Isabelle Suter-Widmer1,2, Philipp Schuetz2,3, Birsen Arici1,2, Martina Bally2,3, Claudine A Blum2,3, Christian H Nickel2,4, Roland Bingisser2,4, Andreas Bock2,5, Andreas Huber2,6, Beat Müller2,3, Mirjam Christ-Crain1,2. 1. Endocrinology, Diabetology and Metabolism, University Hospital Basel, Basel, Switzerland. 2. Department of Clinical Research, University Hospital Basel, Basel, Switzerland. 3. Medical University Clinic and Divisions of Endocrinology, Diabetology and Metabolism, Kantonsspital Aarau, Aarau, Switzerland. 4. Emergency Medicine, University Hospital Basel, Basel, Switzerland. 5. Nephrology, Dialysis & Transplantation, Kantonsspital Aarau, Aarau, Switzerland. 6. Institute of Laboratory Medicine, Kantonsspital Aarau, Aarau, Switzerland.
Abstract
OBJECTIVE: Hyponatraemia is common and its differential diagnosis is challenging. Commonly used diagnostic algorithms have limited diagnostic accuracy. Copeptin, the c-terminal portion of the precursor peptide of arginine vasopressin might help in the differential diagnosis of hyponatraemia. DESIGN: Prospective multicentre observational study. PATIENTS/ METHODS: A total of 298 patients admitted with profound hypoosmolar hyponatraemia (Na < 125 mmol/l) were evaluated. Three experts uninvolved in the patients' care determined the aetiology of hyponatraemia after standardized diagnostic evaluation. RESULTS: Hyponatraemia differential diagnoses were as follows: syndrome of inappropriate antidiuresis (SIAD), 106 patients (35·6%); 'diuretic-induced', 72 (24·2%); 'hypovolaemic', 59 (19·8%); 'hypervolaemic', 33 (11·1%); primary polydipsia (PP), 24 (8·1%); and cortisol deficiency, 4 (1·3%). Copeptin levels <3·9 pmol/l identified patients with PP with high specificity (91%). Further, copeptin levels >84 pmol/l were highly predictive for hypovolaemic hyponatraemia (specificity: 90%). Urinary sodium levels and copeptin/urinary sodium ratio in patients with SIAD were higher and lower as compared to other hyponatraemia aetiologies (P < 0·0001). However, the specificity to identify SIAD was moderate for both parameters (31% and 61%). Fractional uric acid excretion (FEUA ) and fractional urea excretion (FEurea ) were higher in patients with SIAD compared to other hyponatraemia aetiologies (both P < 0·0001). FEurea values >55% and FEUA values >12% had a specificity of 96% and 77% to detect patients with SIAD. These results remained similar after excluding patients taking diuretics. CONCLUSIONS: Overall, there is only limited diagnostic utility of copeptin in the differential diagnosis of profound hyponatraemia. Very low copeptin levels are seen in patients with PP and highest copeptin levels in hypovolaemic hyponatraemia. To discriminate between SIAD and other hyponatraemia aetiologies, FEurea and FEUA levels are valuable irrespective of diuretics use.
OBJECTIVE: Hyponatraemia is common and its differential diagnosis is challenging. Commonly used diagnostic algorithms have limited diagnostic accuracy. Copeptin, the c-terminal portion of the precursor peptide of arginine vasopressin might help in the differential diagnosis of hyponatraemia. DESIGN: Prospective multicentre observational study. PATIENTS/ METHODS: A total of 298 patients admitted with profound hypoosmolar hyponatraemia (Na < 125 mmol/l) were evaluated. Three experts uninvolved in the patients' care determined the aetiology of hyponatraemia after standardized diagnostic evaluation. RESULTS: Hyponatraemia differential diagnoses were as follows: syndrome of inappropriate antidiuresis (SIAD), 106 patients (35·6%); 'diuretic-induced', 72 (24·2%); 'hypovolaemic', 59 (19·8%); 'hypervolaemic', 33 (11·1%); primary polydipsia (PP), 24 (8·1%); and cortisol deficiency, 4 (1·3%). Copeptin levels <3·9 pmol/l identified patients with PP with high specificity (91%). Further, copeptin levels >84 pmol/l were highly predictive for hypovolaemic hyponatraemia (specificity: 90%). Urinary sodium levels and copeptin/urinary sodium ratio in patients with SIAD were higher and lower as compared to other hyponatraemia aetiologies (P < 0·0001). However, the specificity to identify SIAD was moderate for both parameters (31% and 61%). Fractional uric acid excretion (FEUA ) and fractional urea excretion (FEurea ) were higher in patients with SIAD compared to other hyponatraemia aetiologies (both P < 0·0001). FEurea values >55% and FEUA values >12% had a specificity of 96% and 77% to detect patients with SIAD. These results remained similar after excluding patients taking diuretics. CONCLUSIONS: Overall, there is only limited diagnostic utility of copeptin in the differential diagnosis of profound hyponatraemia. Very low copeptin levels are seen in patients with PP and highest copeptin levels in hypovolaemic hyponatraemia. To discriminate between SIAD and other hyponatraemia aetiologies, FEurea and FEUA levels are valuable irrespective of diuretics use.