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

BackgroundThe in vitro stability of N-terminal (NT)-proBNP (brain natriuretic peptide) at room temperature and at 4°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.MethodsNT-proBNP was measured on 97 heparinized samples before and after a two-year frozen storage (−20°C) using the Roche Elecsys system.ResultsThere 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-proBNPstored sample = 0.93 NT-proBNPfresh sample + 81. A similar equation was found in lower concentrations (NT-proBNP ≤ 2000 ng/L).ConclusionsThese data show that NT-proBNP can be stored for at least two years at −20°C before measurement w...