The in vitro stability of both BNP and NT-proBNP is sufficient for routine clinical use. The in vitro stability of BNP is dependent on the assay used for determination (see Issues for Assay Development). BNP is stable in EDTA whole blood at room temperature for 4 h (Biosite and Abbott assays), and at 4°C for 24 h (Bayer assay). EDTA plasma is stable at 4°C for 24 (Abbott assay) and 48 h (Bayer assay). A significant decrease in plasma BNP concentrations was noted when BNP was measured after 24 h of storage at 4°C with the Biosite assay (12). If samples are not to be analyzed within several hours, it is recommended that the plasma be frozen at or below -20°C.
NT-proBNP is stable in whole blood or in EDTA or heparinized plasma samples for 2 to 3 d at room temperature (18,19). NT-proBNP is stable in serum samples if serum is separated from cells within 24 h. NT-proBNP is stable in serum or plasma samples for several days at 4oC and for 12 mo at or below -20°C (12,18,19).
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