BACKGROUND AND OBJECTIVE The aim of this study was to assess the performance of N-terminal proB-type natriuretic peptide (NT-proBNP) levels for the diagnosis of left ventricular dysfunction in patients with severe acute exacerbations of chronic obstructive pulmonary disease (COPD) and renal dysfunction. METHODS NT-proBNP levels at admission were measured in consecutive patients admitted to two participating intensive care units with acute exacerbations of COPD. Left ventricular dysfunction was assessed on the basis of clinical and echocardiographic criteria. The performance of NT-proBNP levels was evaluated in patients with or without renal dysfunction. RESULTS Among the 120 patients included in the study, 70 had impaired renal function, defined as a glomerular filtration rate of <90 mL/min/1.73 m(2). NT-proBNP levels were inversely correlated with glomerular filtration rate (Spearman's correlation coefficient = -0.457, P < 0.001). Overall, left ventricular dysfunction was diagnosed in 58 patients (48.3%). Median NT-proBNP levels were significantly higher in these patients, irrespective of whether their renal function was normal (3313 (interquartile range (IQR) 4603) vs 337 (IQR 695) pg/mL, P < 0.001) or impaired (5692 (IQR 10714) vs 887 (IQR 1165) pg/mL, P < 0.001). The areas under the receiver operating characteristic curves were 0.87 and 0.78, respectively. The threshold NT-proBNP value with the highest diagnostic accuracy was greater in the setting of renal dysfunction (2000 pg/mL; sensitivity 71%, specificity 82%, compared with 1000 pg/mL in patients with normal renal function; sensitivity 94%, specificity 82%). Multivariate analysis showed that left ventricular dysfunction and glomerular filtration rate were independently associated with elevated NT-proBNP levels. CONCLUSIONS NT-proBNP remains an accurate biomarker for the diagnosis of left ventricular dysfunction associated with acute exacerbations of COPD. Threshold values of NT-proBNP were higher in patients with impaired renal function than in those with normal renal function.