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

Abstract

B-type natriuretic peptide (BNP) is a 32 amino acid cardiacsynthesized hormone that reduces blood pressure and increases sodium excretion (1 ). Following proteolytic cleavage of proBNP, a 108-amino acid precursor, an Nterminal 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 crossreactivity with NT-proBNP or proBNP, and (b) whether NTproBNP assays demonstrated crossreactivity 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 NTproBNP, 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, OrthoClinical 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) EDTAplasma 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 crossreactivity 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.Recoveries and cross-reactivity percentages between peptides and BNP and NT-proBNP assays are displayed in Table 1. The BNP assays were more specific for the BNP peptides, with recovery ranging from 79% to 199%, compared to 5% to 38% cross-reactivity to the proBNP peptides and Ͻ1% to 7% cross-reactivity to the NTproBNP peptides. Similarly, the NT-proBNP assays were more specific for the NT-proBNP peptides, showing 47% to 243% recovery, with substantial crossreactivity to proBNP peptides (Ͻ1% to 249%), and no crossreactivity to the BNP peptides (Ͻ1% across all assays).This study demonstrates th...

Circulating N-terminal pro-B-type natriuretic peptide in fetal anemia before and after treatment

“…However, values are assay-specific with limited comparability (11,12). In addition, cross-reactivity with pro-BNP, the precursor form with six-to eightfold lower biological activity, and glycosylated forms of BNP has been demonstrated (13). This is of particular importance as patients with heart failure have evidence of increased levels of circulating pro-hormone (14,15).…”

Natriuretic Peptides and Analytical Barriers

“…Indeed, there is extensive variation depending upon the nature of the natriuretic peptide calibrators used and their glycosylation ( Table 2). Cross-reactivity of BNP with proBNP was also demonstrated; this is particularly important in HF patients since proBNP is more prevalent in these patients (36 ). A summary of crossreactivity of BNP and NT-proBNP assays currently in clinical use is presented in Fig.…”

New issues on measurement of B-type natriuretic peptides

“…Moreover, a recent study [34] suggested that the commercial immunoassays, commonly used for NTproBNP assay, employ non-glycosylated calibrator materials and mostly antibodies directed against epitopes with potential O-glycosylation site occupancy. Because the most part of circulating inactive peptides related to NT-proBNP and proBNP are O-glycosylated [7,18,35], these immunoassays cannot measure some glycosylated peptides [34,36]. Moreover, the commercially available immunoassays for NT-proBNP are interfered by the intact peptide proBNP (especially non-glycosylated peptide) [36] and also by some other shorter peptides derived from the proteolytic degradation of this pro-hormone [1] (Figure 2).…”

“…Because the most part of circulating inactive peptides related to NT-proBNP and proBNP are O-glycosylated [7,18,35], these immunoassays cannot measure some glycosylated peptides [34,36]. Moreover, the commercially available immunoassays for NT-proBNP are interfered by the intact peptide proBNP (especially non-glycosylated peptide) [36] and also by some other shorter peptides derived from the proteolytic degradation of this pro-hormone [1] (Figure 2). In conclusion, the commercially available immunoassays for NT-proBNP do not allow an accurate measurement of this peptide.…”

“…In addition to the peptide hormone BNP and the inactive peptide NT-proBNP, a huge numbers of other circulating peptides derived from the pro-hormone proBNP can be identified by chromatographic procedures in human plasma, including the intact and glycosylated forms of proBNP itself [29][30][31][32][33]38] (Figure 2). Furthermore, the active hormone BNP may be produced even in vivo from the circulating intact precursor proBNP through enzymatic cleavage by some plasma proteases (such as corin) [35,36,39] (Figure 2). Indeed, a recent study, using an in vivo experimental rat model, demonstrated that the split of proBNP into BNP and NT-proBNP can actually occur in circulation [40].…”