RESUMO
BACKGROUND: Clinical trial samples may be stored frozen for prolonged periods before analysis, which can reduce the immunoreactivity of numerous analytes, particularly peptides. We sought to determine the effect of 6 years of frozen storage on serum N-terminal pro-B-type natriuretic peptide (NT-proBNP). METHODS: NT-proBNP was measured from serum samples taken from 99 different patients enrolled in the CanPREDDICT study after <1 year of storage at -70 °C using the Roche first-generation NT-proBNP assay on an e411 instrument. Separate aliquots of the same samples were analyzed after an additional 6 years of storage at -70 °C using the Roche second-generation assay on an e601 instrument. RESULTS: The median NT-proBNP immunoreactivity for the first measurement was 572 pg/mL (interquartile range [IQR] 205-1606, range 49-12820), while after an additional 6 years of storage at -70 °C, this value decreased to 526 pg/mL (IQR 181-1338, range 18-12880), resulting in a median percent difference of -7% (IQR -10.6% to -3.4%, P < 0.001). CONCLUSIONS: We report findings consistent with trends seen in previous work but have investigated the effect of a much longer storage period. Larger percent decreases in NT-proBNP reaching statistical significance are seen, although the median difference is still <10%.
