Copeptin is a reliable biomarker of vasopressin and is associated with urine osmolality in patients on peritoneal dialysis

Abstract Background Vasopressin, a hormone regulating water metabolism, has been poorly studied in patients on peritoneal dialysis (PD). Vasopressin measurement is challenging and not routinely available in clinical practice. This study aimed to evaluate whether copeptin, a stable surrogate marker of vasopressin, could be used to assess vasopressin levels in patients on PD and to determine if vasopressin maintains its antidiuretic effect in this population. Methods We included 34 PD patients from three French nephrology centers. Plasma vasopressin was measured using radioimmunoassay, while copeptin was quantified with a non-competitive immunofluorescence assay. Urine osmolality and 24-hour urine output were assessed, and peritoneal adequacy tests were performed. Associations between copeptin, vasopressin, and clinical parameters were analyzed using Spearman correlations and mixed-effect models. Healthy controls were included for comparison. Results Copeptin levels were strongly correlated with vasopressin levels (Spearman's rho = 0.62, P 0.001), confirming its reliability as a biomarker of vasopreassin. Higher copeptin levels were associated with increased urine osmolality (β = 3.63, P = 0.008) and decreased 24-hour urine output (β = −0.53, P = 0.008), indicating that vasopressin retains its antidiuretic activity in PD patients. Compared to healthy controls, PD patients had lower urine osmolality and required higher copeptin levels to achieve similar urine concentration, suggesting vasopressin resistance. Copeptin levels were also associated with lower residual kidney function and higher brain natriuretic peptide levels but were not influenced by blood pressure, plasma sodium, or PD characteristics. Conclusions This study provides evidence that vasopressin maintains an antidiuretic effect in PD patients, and supports the use of copeptin as a robust biomarker for vasopressin in this population.