Evaluation of performance of a rapid immunofluorescence method for assaying plasma NT-proBNP

Abstract

Objective To analyze the performance of a rapid immunofluorescence assay for plasma NT-proBNP. Methods Human plasma NT-proBNP was measured by RAMP in 264 healthy cases and 78 patients with heart failure. The precision, stability, linearity and interference factors of RAMP were evaluated according to the protocold from America CLSI. Meanwhile, the results were compared with those obtained by Elecsys. Results Functional sensitivity of RAMP in 20% CV and 10% CV were 48 ng/L and 57 ng/L respectively. The linear range was 18-8 000 ng/L. NT-proBNP in plasma samples detected by RAMP were stable at room temperature for 24 hours, 4 ℃ for 3 days and - 20 ℃ for 20 days. No influences on results were observed throughout three freeze-thaw cycles. The results measured by RAMP were compared between EDTA-K2 anticoagulant plasma and heparin anticoagulant plasma, which showed that YEDTA-K2 =0. 953 9 Xheparin + 0. 365 2 ( R2 = 0. 982, P < 0. 01, n = 40 ). The results of EDTA-K2 and heparin anticoagulant plasma using RAMP and Elecsys showed no significant difference( P ＞0. 05). Slight hemolysis( Hb 2 g/L)had small effect on the results of PAMP and Elecsys assays and deviations of them were below 5%. However median and heavy hemolysis( Hb 3-4 g/L )obviously influenced the results with deviation were more than 15%. The values measured by RMAP fell from 390 ng/L to 82 ng/L, and those measured by Elecsys method fell from 390 ng/L to 178 ng/L when 3 different concentrations of triacylglycerol were added, the values measured by two methods fell from 7 777 ng/L to 7 741 ng/L when bilirubin ( 16-330 μmol/L) was added. The anti-interference ability of RAMP method was similar to Elecsys. Results detected with two methods in 45 EDTA-K2 anticoagulant plasma samples were analyzed with Passing and Bablok regression.The regression equation was YRAMP = 0. 972 8XElecsys - 0. 035 2 (R2 = 0. 994, P ＞ 0. 05, n = 45 ). When heparin anticoagulant plasma samples increased to 78 samples, Passing and Bablok regression equation showed:YRAMP= 0. 983 2XElecsys - 0. 037 6 ( R2 = 0. 991, P ＞ 0. 05, n = 78 ). NT-proBNP levels in healthy adults were elevated along with age and related to the gender. The median value of female[105(60-120) ng/L] was higher than that of male [59 ( 44-91 ) ng/L, Z = 3. 264, P < 0. 01] significantly. Conclusions RAMP method has good repeatability, outstanding stability, and broad linear range. The results detected by RAMP is consistent with results detected by Elecsys. Key words: Peptide fragments; Natriuretic peptide, brain; Fluoroimmunoassay; Heparin; Evalution studies