Evaluation of the Randox full range C reactive protein assay on the Abbott Aeroset system

The reference interval for C reactive protein (CRP) is approximately 0-6 mg/L with concentrations of 10-40 mg/L associated with mild inflammation and concentrations of 40-200 mg/L found in acute inflammation and bacterial infection. Elevated CRP levels within the 0-6 mg/L interval have been implicated in cardiovascular morbidity and mortality and serial CRP levels within this range are also useful in early neonatal sepsis as a guide to antibiotic therapy. A recently developed CRP assay (Randox Laboratories, Crumlin, N Ireland) with a reported range of 0-160 mg/L has been adapted for use on our high throughput automated analyser, Abbott Aeroset. At mean concentrations of 2.18, 4.89 and 22.10 mg/L, intra-assay imprecision was 1.10%, 0.91%, 1.01%, n=20. Between-assay imprecision was 1.82%, 1.85%, (n=95) at mean concentrations of 2.18, 4.93 mg/L and 2.38% at a mean of 21.50 mg/L (n=70). Linearity assessed by comparison of triplicate assays of a serially diluted control and comparison of expected and measured results was 1.6-172 mg/L. Detection limit determined by the mean of 20 replicates of saline plus 2 SD of 20 replicates of the lowest concentration calibrator was 0.05 mg/L. Functional sensitivity assessed by analysis of 10 replicates of 5 patient specimens diluted to near the expected limit of detection range showed %CVs of 12.2, 11.2, 13.9, 17.7, 28.1 at means of 0.30, 0.25, 0.18, 0.10, 0.09 mg/L respectively. Functional sensitivity is therefore around 0.10 mg/L Duplicates of 12 NEQUAS samples showed the % mean bias from the all laboratory trimmed mean ranged from (-2.5%) at a mean concentration of 1.2 mg/L to (-0.92%) at 134.1 mg/L with a maximum on one control of 19.5% at a concentration of 15.9 mg/L. CRP in the clinically useful range can be measured quickly and reliably on the Aeroset analyser within and outside normal working hours.