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Kristin N Luckenbill, Robert H Christenson, Allan S Jaffe, Johannes Mair, Jordi Ordonez-Llanos, Franca Pagani, Jillian Tate, Alan H B Wu, Ranka Ler, Fred S Apple, Cross-Reactivity of BNP, NT-proBNP, and proBNP in Commercial BNP and NT-proBNP Assays: Preliminary Observations from the IFCC Committee for Standardization of Markers of Cardiac Damage, Clinical Chemistry, Volume 54, Issue 3, 1 March 2008, Pages 619–621, https://doi.org/10.1373/clinchem.2007.097998
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To the Editor:
B-type natriuretic peptide (BNP) is a 32 amino acid cardiac-synthesized hormone that reduces blood pressure and increases sodium excretion (1). Following proteolytic cleavage of proBNP, a 108-amino acid precursor, an N-terminal fragment (NT-proBNP) and BNP are released (2). Increased concentrations of BNP and NT-proBNP can be used clinically to monitor heart failure, but a lack of alignment between commercial BNP and NT-proBNP assays (3) can lead to confusion when clinicians or laboratorians compare results measured for the same analyte on different instruments. Some of this confusion arises from variable assay specificity regarding what peptides are being measured. We studied whether (a) BNP assays demonstrated cross-reactivity with NT-proBNP or proBNP, and (b) whether NT-proBNP assays demonstrated cross-reactivity with BNP or proBNP, by using 5 commercial BNP and 3 commercial NT-proBNP assays with 2 BNP, 2 NT-proBNP, and 2 proBNP materials.
The NPs studied were: Peptide Institute synthetic BNP (aa 77–108), Scios human recombinant BNP (aa 77–108), HyTest human recombinant NT-proBNP (aa 1–76), Roche modified (amidated for stabilization) synthetic NT-proBNP, HyTest human recombinant proBNP (aa 1–108), and Scios glycosylated human recombinant proBNP. BNP assays evaluated were Abbott Architect, Abbott AxSYM, Bayer Centaur, Biosite Triage, and Beckman Access (Biosite assay packaged for use by Beckman). NT-proBNP assays (all based on Roche reagents) were Dade-Behring Dimension, Ortho-Clinical Diagnostics Vitros, and Roche Elecsys 2010. All assays, for which epitopes of the antibodies used have been previous described (3), were run according to the manufacturers’ guidelines. BNP, NT-proBNP, and proBNP materials were diluted with normal (low NP concentration) EDTA-plasma pools and lithium-heparin plasma (Dade assay only) pools, collected from healthy donors after institutional review board approval was obtained, to achieve target concentrations of 250, 500, and 1000 ng/L. Baseline BNP and NT-proBNP were quantified first in the pools and then after the pools were spiked with NP peptides. All measurements were performed in duplicate. Baseline BNP or NT-proBNP concentrations were subtracted from each spiked pool measurement. Percent cross-reactivity was calculated by dividing the measured concentration for the spiked pool into the expected peptide concentration, multiplying by 100, and then averaging across all 3 expected concentrations.
