To the Editor:
Blood measurements of B-type natriuretic peptide (BNP), a cardiac neurohormone, are proposed as a diagnostic and prognostic aid in congestive heart failure (CHF) and as a prognostic marker in acute coronary syndromes (ACS) (1). In addition, there are preliminary data indicating a possible role of BNP as an aid in guiding medical therapy in patients with CHF (2)(3). The growing interest in clinical determination of BNP has led to the development of immunoassays for the determination of this analyte that are suitable for fully automated, high-throughput clinical instruments with random access, e.g., the ADVIA Centaur BNP (Bayer Diagnostics) and AxSYM BNP (Abbott Laboratories). We aimed to perform a preliminary analytical evaluation of the recently developed AxSYM BNP assay and to compare its clinical performance with that of the ADVIA Centaur BNP assay. The properties of the ADVIA Centaur BNP assay have been reported previously (4).
As indicated by the manufacturer, the AxSYM BNP assay, produced by Axis-Shield plc for Abbott Laboratories, is a fully automated microparticle enzyme immunoassay that uses two monoclonal mouse antibodies in a two-step sandwich format. The analyte is captured on anti-BNP-coated latex microparticles with detection via alkaline phosphatase and measurement of fluorescence produced from the breakdown of 4-methylumbelliferyl phosphate substrate. The solid-phase antibody is directed at the NH2 terminus of the BNP peptide, whereas the conjugate antibody is directed at the COOH terminus. Six calibrators are used for the AxSYM BNP assay. Calibrator A is an acetate buffer with protein stabilizers. Calibrators B–F contain increasing concentrations of synthetic BNP (100, 400, 1000, 2000, and 4000 ng/L) in acetate buffer with protein stabilizers. These calibrators are traceable to a reference standard that was prepared gravimetrically with synthetic BNP; the reference standard underwent a value assignment to align with the Biosite Triage BNP assay …
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