Copeptin and arginine vasopressin concentrations in critically ill patients.

CONTEXT Determination of arginine vasopressin (AVP) concentrations may be helpful to guide therapy in critically ill patients. A new assay analyzing copeptin, a stable peptide derived from the AVP precursor, has been introduced. OBJECTIVE Our objective was to determine plasma copeptin concentrations. DESIGN We conducted a post hoc analysis of plasma samples and data from a prospective study. SETTING The setting was a 12-bed general and surgical intensive care unit (ICU) in a tertiary university teaching hospital. PATIENTS Our subjects were 70 healthy volunteers and 157 ICU patients with sepsis, with systemic inflammatory response syndrome (SIRS), and after cardiac surgery. INTERVENTIONS There were no interventions. MAIN OUTCOME MEASURES Copeptin plasma concentrations, demographic data, AVP plasma concentrations, and a multiple organ dysfunction syndrome score were documented 24 h after ICU admission. RESULTS AVP (P < 0.001) and copeptin (P < 0.001) concentrations were significantly higher in ICU patients than in controls. Patients after cardiac surgery had higher AVP (P = 0.003) and copeptin (P = 0.003) concentrations than patients with sepsis or SIRS. Independent of critical illness, copeptin and AVP correlated highly significantly with each other. Critically ill patients with sepsis and SIRS exhibited a significantly higher ratio of copeptin/AVP plasma concentrations than patients after cardiac surgery (P = 0.012). The American Society of Anesthesiologists' classification (P = 0.046) and C-reactive protein concentrations (P = 0.006) were significantly correlated with the copeptin/AVP ratio. CONCLUSIONS Plasma concentrations of copeptin and AVP in healthy volunteers and critically ill patients correlate significantly with each other. The ratio of copeptin/AVP plasma concentrations is increased in patients with sepsis and SIRS, suggesting that copeptin may overestimate AVP plasma concentrations in these patients.