Two-year stability of NT-proBNP in frozen samples using the Roche Elecsys system

BACKGROUND: The in vitro stability of N-terminal (NT)-proBNP (brain natriuretic peptide) at room temperature and at 4 degrees C is excellent and has been well studied. However, less is known concerning its stability after a long-term frozen storage. This notion could be of major interest in the context of clinical evaluations. METHODS: NT-proBNP was measured on 97 heparinized samples before and after a two-year frozen storage (-20 degrees C) using the Roche Elecsys system. RESULTS: There is a slight but significant decrease of NT-proBNP concentration after frozen storage. However, this decrease is <10% for more than 90% of the samples and the maximum decrease is 16%. Moreover, values on frozen samples are well correlated with values on fresh samples (r = 0.99) using the following equation: NT-proBNP(stored sample) = 0.93 NT-proBNP(fresh sample) + 81. A similar equation was found in lower concentrations (NT-proBNP < or = 2000 ng/L). CONCLUSIONS: These data show that NT-proBNP can be stored for at least two years at -20 degrees C before measurement without a substantial loss of immunoreactivity.