Copeptin: Utility in Paediatric Patients with Hyponatraemia.

INTRODUCTION: Copeptin concentrations are a useful component of the diagnostic workup of paediatric patients with polyuria and polydipsia, but the value of measuring copeptin in patients with hyponatraemia is less clear.

CASE REPORTS: We report 5 children with hyponatraemia in the context of different underlying pathologies. Copeptin concentrations were elevated in 4 cases (13.7, 14.4, 26.1, and 233 pmol/L; reference range 2.4-8.6 pmol/L), suggesting that non-osmoregulated vasopressin release (syndrome of inappropriate antidiuretic hormone) was the underlying mechanism for low sodium levels. In one of the patients, there was an underlying diagnosis of Schaaf-Yang syndrome (MAGEL2 gene mutation) with a clinical picture suggestive of dysregulated vasopressin production with inappropriately high and then low copeptin release. In one hyponatraemic patient, low copeptin concentrations indicated that non-osmoregulated arginine vasopressin release was not the cause of hyponatraemia and oliguria.

DISCUSSION: Copeptin measurement did not influence management acutely but helped to clarify the mechanism leading to hyponatraemia when the result was available. Relatively high and low copeptin concentrations in association with hypo- and hypernatraemia indicate dysregulated vasopressin production in Schaaf-Yang syndrome.