NPPB and congestive heart failure: However, there is a limited number of studies addressing natriuretic peptide variability, and these works have evaluated the biological variation of BNP and NT-proBNP concentrations in both patients with chronic heart failure and healthy people over a short (within a day, week to week and month to month) and intermediate (1-month, 2-month, and 3-month) interval of time [8]–[11].