Disparity between studies of the stability of BNP in blood: comparison of endogenous and exogenous peptide

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Abstract
Blood was withdrawn from a forearm vein of 10 healthy volunteers (eight men, mean age 38 years) and divided directly into three chilled polypropylene tubes containing EDTA (1 mg/ml blood) and aprotinin (50 kIU/ml blood). The first sample was stored without the addition of exogenous BNP; 350 pg/ml of human BNP was added to the second sample; and the third sample was separated in a refrigerated centrifuge before the addition of the same concentration of BNP. Each sample was subsequently divided again into two aliquots; the first being separated, if necessary, and frozen immediately to −20°C (control), and the second stored at room temperature (22°C) for 72 hours. All samples were analysed in a single batch, in duplicate, without prior extraction of plasma using a direct, specific, monoclonal antibody kit as previously described.2 The aliquots frozen immediately were used to compare the data for samples stored at room temperature.