NTproBNP measurement and interpretation
Venous blood samples were obtained using a standard venipuncture technique. Specimens were analysed within 1 h of venipuncture whenever possible. When immediate analysis was not possible, blood samples were centrifuged and the serum was frozen at −80°C for later analysis. Plasma NTproBNP levels were measured using a commercially available immunofluorescent assay (Elecsys proBNP, Roche Diagnostics, Mannheim, Germany). The assay has a functional sensitivity of 30 pg/ml, with an upper measuring limit of 35 000 pg/ml and a coefficient of variation in the range 1.0–6.0%.