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Figure 1 Differences in Measurement of proBNP Between the Processing-Independent Assay and the Roche Assay

(A) Summary of the processing-independent assay (PIA) for measurement of pro-B-type natriuretic peptide (proBNP) 1-108 and 1-76. During analysis, both peptides are cleaved with an endoprotease (trypsin) releasing an N-terminal fragment (proBNP 1-21, red boxes). The larger, blue boxes represent the glycosylated midregion in proBNP. Note that both proBNP 1-108 and 1-76 will be quantified with equal affinity and irrespective of the glycosylation degree. (B) The N-terminal (NT)-proBNP assay by Roche (Karlsruhe, Germany). Two antibodies raised against distinct regions in proBNP 1-76 are used in a sandwich assay. One antibody is raised against the glycosylated region in endogenous proBNP. The assay is calibrated with synthetic, nonglycosylated proBNP 1-76, and the assay affinity to proBNP 1-108 is unknown.