Performance characteristics of a point of care C-reactive protein assay

C-reactive protein (CRP) is a non-specific marker of inflammation that can be used for atherosclerotic risk assessment. This application requires increased precision at low CRP concentrations compared to traditional assays.

The Micros CRP analyzer (ABX Diagnostics) is a small bench top device. Its limit of detection, limit of quantitation, linearity and imprecision were assessed. Method comparison studies were performed using samples both inside and outside the reference interval. Anticoagulant effects and the prozone effect were also evaluated.

The limit of detection was 0.1 mg/l. The method was linear from 2 to 60 and 0.3 to 60 mg/l using systematic error limits of 10% and 20%, respectively. The total imprecision was <8% for CRP concentrations from 0.7 to 9.1 mg/l. A prozone effect was seen at CRP concentrations >500 mg/l. Using samples from 120 apparently healthy adults, the Micros CRP method demonstrated excellent concordance with the BN II high sensitivity CRP (hs-CRP) method. The Micros CRP method compared well with a nephelometric method using samples with elevated CRP concentrations.

The Micros CRP method is adequate for atherosclerotic risk prediction in clinical practice but does not have adequate accuracy at CRP concentrations <2 mg/l for epidemiological studies.