ANALYTICAL EVALUATION OF PARTICLE-ENHANCED IMMUNONEPHELOMETRIC ASSAYSFOR C-REACTIVE PROTEIN, SERUM AMYLOID-A AND MANNOSE-BINDING PROTEIN IN HUMAN SERUM

Against a background of growing interest in more sensitive assays for quantifying various acute phase proteins, we evaluated the performance of recently developed tests for C-reactive protein (CRP), serum amylo id A (SAA) and mannose-binding protein (MBP) on the Behring nephelomet er II (BN II). Sample results outside the calibration ranges of 3.5 to 220 mg/L for CRP, 3.3 to 215 mg/L for SAA and 0.09 to 5.6 mg/L for MB P were automatically re-measured at another dilution. The lower limits of detection were 0.01, 0.7 and 0.01 mg/L for CRP, SAA and MBP, respe ctively. The coefficients of variation (CV) for intra- (n greater than or equal to 20) and inter- (n greater than or equal to 15) assay prec ision were <5.2% and <8.5%, respectively, for the three proteins at co ncentrations representing low, normal and high. Linearity for each met hod was within 5% of the expected values throughout the calibration ra nge. We observed no significant interference from bilirubin (up to 300 mg/L) or haemoglobin (up to 10 g/L) for the three tests. Method compa rison studies performed for CRP and SAA yielded the following results: y (CRP on BN II) = 0.75x (ELISA, Hemagen) -0.25 mg/L (r = 0.981, S-y/ x = 2.1 mg/L; y (SAA on BN II) = 1.44x (ELISA, Hemagen) -9.9 mg/L (r = 0.972, S-y/x = 6.9 mg/L), where ELISA is enzyme-linked immunosorbent assay. Reference intervals established in 261 adult blood donors (aged 36.2 +/- 9.0 years) were found to be log-normal with 2.5th, 50th and 97.5th centiles of <0.17, 1.00 and 10.1 mg/L for CRP, <0.84, 2.10 and 9.70 mg/L for SAA; and 0.30, 1.28 and 4.10 mg/L for MBP. We observed n o relationship with CRP concentration and age; however, SAA levels inc reased with age while MBP levels decreased. The BN II provides a simpl e, rapid and sensitive system for measuring CRP, SAA and MBP in human serum.