Analytical performance and clinical results of a fully automated MEIA system for brain natriuretic peptide assay: comparison with a point of care testing method

The aim of this study was to evaluate the analytical performance of a recently available immunoassay for brain natriuretic peptide (BNP), based on microparticle enzyme immunoassay (MEIA, AxSYM System, Abbott Laboratories), whose analytical characteristics and clinical results were compared with those of a point of care testing (POCT) method (TRIAGE system, Biosite Diagnostics). The withinrun and total imprecision of the MEIA system were 18.4% and 19.8% at 21 ng/l, 8.0% and 14.8% at 183 ng/l, and 5.7% and 14.0% at 319 ng/l, respectively. The detection limit of the MEIA system was tested by repeatedly measuring (n=20) the 0 calibrator in four different runs; a mean +3 SD value of 5.6 +/- 4.8 ng/l (range 1.8-12.6 ng/l) was obtained. A close linear relationship (MEIA= 22.5+1.71 POCT method, R=0.950, n=296) was found (BNP concentration: 5-5500 ng/l), with a significant bias (mean difference: 164.8 ng/l, p<0.0001). Mean BNP concentration measured in 94 reference subjects (57 women and 37 men; mean age 43.5 +/- 14.0 years) was higher with MEIA than POCT, (25.9 +/- 32.7 ng/l vs. 11.7 +/- 8.9 ng/l, p<0.0001). The same trend was observed also in 202 cardiac patients (620.6 +/- 1082.2 ng/l vs. 386.1 +/- 594.5 ng/l, p<0.0001). Our data suggest that MEIA and POCT have quite similar analytical performance but different clinical results. Then, different reference values, as well as cutoff values, should be taken into account for the clinical use of these two immunoassays.