Variability of N-Terminal Probrain Natriuretic Peptide in Stable Chronic Heart Failure and Its Relation to Changes in Clinical Variables

BACKGROUND: We investigated the variability of N-terminal probrain natriuretic peptide (NT-proBNP) and its relation to known Confounding variables in patients with stable chronic heart failure who were on a stable optimized medication regimen. METHODS: At 4 sampling intervals (14-day, 1-month, 2-month, and 3-month) the results for NT-proBNP measurements and several clinical variables were measured in samples from 41 patients with chronic systolic dysfunction who met 21 prespecified criteria for stability. RESULTS: Mean within-person NT-proBNP variabilities expressed as percentage CV were 17.6%, 18.9%, 15.5%, and 16.2% at 14-day, 1-month, 2-month, and 3-month follow-up, respectively, and the corresponding reference change values were 34.6%, 52.5%, 43.1%, and 45.0%, respectively. Within-person variability of NT-proBNP was not found to be associated with renal function, weight, or waist circumference. Likewise) age, sex, baseline NT-proBNP, New York Heart Association functional class, and ejection fraction did not influence variability of NT-proBNP. The index of individuality ranged from 0.07-0.15 depending on the time interval between test results. CONCLUSIONS: Although other reported studies have revealed variations in the range of 80%, in this prespecified stable heart-failure population variation of NT-proBNP at 14-day, 1-month, 2-month, and 3-month follow-up was lower and was not related to renal function or weight. In view of the low index of individuality we observed, within-person variation is quite low compared to between-person variation. Consideration of these facts is important for the interpretation of clinical trials and the use of NT-proBNP in monitoring patients with heart failure. (C) 2009 American Association for Clinical Chemistry.