Comparison and evaluation of two C-reactive protein assays based on particle-enhanced immunoturbidimetry

The use of C-reactive protein (CRP) assays is increasing for a wide range of clinical conditions, and consequently the analytical performance requirements for CRP assays are also changing. For this reason, manufacturers have been developing CRP assays based on different methodologies to provide both high sensitivity and a wide measuring range. However, it is questionable whether these methods can meet the desired requirements for CRP assays. CRP Latex on the Cobas Integra 400 and CRP Tina-quant Latex on the Modular Analytics-P were evaluated in terms of detection limit, linearity, intra- and interassay precision, and comparability with 268 patient samples. The intra- and interassay precision of the two methods was <4.1% in the three pools with CRP concentrations ranging from 6.9 to 215 mg/L, and >10% in the pool with concentrations of approximately 0.60 mg/L. The detection limits for CRP Latex and Tina-quant Latex were 0.20 and 0.22 mg/L, respectively. Both methods were linear up to 215 mg/L. There was a good agreement between the two assays, except for a scattering at concentrations near the detection limits. Deming regression analysis for CRP Latex (x-axis) and Tina-quant Latex (y-axis) yielded a slope of 1.067+/-0.018, an intercept of -0.148+/-0.358, and an S(y/x) of 5.10 (r=0.996, P<0.0001). The two assays gave comparable results. Low precision was determined for both assays, except for the low pool with a concentration of approximately 0.60 mg/L. We concluded that both of these assays should be improved to meet high-sensitivity criteria.