Head to head comparison of N-terminal pro-B-type natriuretic peptide and B-type natriuretic peptide in patients with/without left ventricular systolic dysfunction.

BACKGROUND Human pro-B-type natriuretic peptide is cleaved into the active B-type natriuretic peptide (BNP) and the inactive fragment NT-proBNP. It is unclear if, similar to BNP, NT-proBNP can be used as a marker of impaired left ventricular (LV) ejection fraction (EF). This study evaluated the analytical performance of both assays to detect LV systolic dysfunction. METHODS In 72 patients with various degrees of left ventricular systolic dysfunction (LVSD), blood analysis for BNP and NT-proBNP was performed prior to cardiac catheterization, using a point-of-care analyzer (Biosite) and a fully automated laboratory analyzer (Roche-Elecsys), respectively. The within-run and between-run imprecision for BNP and NT-proBNP was calculated. RESULTS Both markers were able to detect impaired LV EF with the largest area under the receiver-operating-characteristic curve for NT-proBNP (NT-proBNP: 0.851 (0.747-0.924); BNP: 0.803 (0.692-0.887) 95% confidence interval; P = 0.07). A significant correlation was observed between BNP and NT-proBNP (r = 0.9; P < 0.0001). Estimating the within-run imprecision, the coefficient of variance for BNP was 3.14% (n = 20, mean 316 ng/L) to 3.32% (n = 20, mean 820 ng/L) and for NT-proBNP 0.9% (n = 20, mean 4390.8 ng/L) to 1.4% (n = 20, mean 225 ng/L). The between-run imprecision for NT-proBNP ranged between 2.1% (n = 20, mean 224.6 ng/L) and 2% (n = 20, mean 4391 ng/L). Optimal discriminator values for BNP and NT-proBNP were 139 ng/L and 358 ng/L, respectively. However, adjusting the BNP cut-off value to 54 ng/L improved the negative predictive value and sensitivity of the assay. CONCLUSION Similar to BNP, NT-proBNP is a promising marker in identifying LVSD. Although both assays are reliable and have good analytical performance, their diagnostic cut-off value is dynamic and population-dependent. The slightly wider detection range and the more stable structure of NT-proBNP compared to the BNP assay suggest that NT-proBNP could play an additional role in the evaluation of patients with LV systolic dysfunction.