Biological variation of the natriuretic peptides and their role in monitoring patients with heart failure

BACKGROUND: B-type natriuretic peptide (BNP) and the inactive metabolite NT-proBNP are proven tests for diagnosis and staging of severity for patients with heart failure. However, the utility of these biomarkers for monitoring the success of drug therapy remains to be determined. Results of longitudinal studies on serial blood testing must be linked to overall patient morbidity and mortality outcomes. We previously determined the 8-week biological variability (BV) of BNP and NT-proBNP assays in healthy subjects and the 1-day BV for BNP alone in patients with compensated and stable heart failure. From these studies, the percent statistical change in serial samples of approximately 100% difference was estimated (95% confidence). METHODS: We applied the biological variability concepts to the serial results of BNP and NT-proBNP collected from patients with heart failure and compared the performance of these two markers. RESULTS: While there are minor differences in the results between the assays from one time period to another, the overall interpretation of results are essentially identical. Moreover, the majority of individual serial time points are not significantly different from the previous value. CONCLUSION: Frequent testing (e.g. daily) for BNP and NT-proBNP to monitor therapy for patients with CHF is not indicated, as overall changes require several days to become evident.