Background: Natriuretic peptides such as N-terminal pro-B-type natriuretic peptide (NT-proBNP) have become increasingly important in diagnosing left ventricular dysfunction (LVD), however, in patients with chronic kidney disease (CKD), their use is confounded by concomitant volume overload and reduced renal excretion. We hypothesized that a serum NT-proBNP cut-off value adjusted for patients with CKD could serve as a biochemical marker to detect LVD in patients on haemodialysis treatment regardless of chronic fluid overload.
Methods: We assessed LV function using trans-thoracic echocardiography and indices of hydration status such as extracellular water (ECW) using bioelectrical impedance analysis (BIA) in 62 stable patients on maintenance haemodialysis. NT-proBNP cutoff values for LVD with different specificities and sensitivities were calculated by ROC curves.
Results: We found a significant inverse correlation between LV ejection fraction (EF) and NT-proBNP levels (r = -0.77, P < 0.0001). In the multivariate regression analysis NT-proBNP was the only independent predictor of EF (r = 0.699, P < 0.0001). NT-proBNP levels were significantly higher (P < 0.0001) in patients with LVD (n = 15; 32 760 +/- 6605 ng/L) compared to those without LVD (n = 47; 2835 +/- 428 ng/L). An NT-proBNP cut-off value of 7168 ng/L resulted in 90% specificity and 79% sensitivity for the presence of LVD, i.e. an EF <45% (AUC(ROC): 0.95 +/- 0.03, P < 0.0001). Furthermore, in patients with LVD we found a significant relationship between serum NT-proBNP and markers of fluid overload such as the ECW/body weight ratio (P < 0.0001) and the grade of peripheral oedema (P = 0.007), but not in patients without LVD.
Conclusion: A serum NT-proBNP cut-off value of >/=7200 ng/L discriminates CKD stage 5 patients without LVD from those with LVD. In those patients with LVD, persistent post-dialytic volume overload correlates with elevated NT-proBNP levels.