Abstract :
[en] The diagnostic and prognostic yields of copeptin, a surrogate biomarker of arginine vasopressin secretion, are currently investigated in various disorders linked to arginine vasopressin regulation, including heart failure, sepsis, or the metabolic syndrome. More specifically, patients with autosomal dominant polycystic kidney disease (ADPKD), which has a prevalence of 1 in 400 to 1000 live births, show significantly higher plasma copeptin levels than controls. Plasma copeptin levels independently correlate with ADPKD progression. Copeptin secretion after hypertonic saline stimulation in patients with ADPKD is unknown. In the study involving 144 patients with hypotonic polyuria, Fenske et al. elegantly show that measuring plasma copeptin after infusion of 3% saline over a period of 3 hours has greater diagnostic accuracy than 17-hour water deprivation. This test will probably replace the water-deprivation test in the diagnostic workup of polyuria, with a copeptin cutoff level of more than 4.9 pmol per liter. It is not clearly mentioned that this cutoff value is a delta — that is, a change in the plasma copeptin level at a plasma sodium level of 147 mmol per liter or more versus baseline. It would have been relevant to provide pretest copeptin levels according to subgroup. Indeed, specific conditions, such as ADPKD, are essentially characterized by an increased plasma copeptin level, a fact that may pragmatically skew the diagnostic yield of copeptin measurement after hypertonic saline stimulation in the challenging context of hypotonic polyuria.
