Performance of automated measurement of antibodies to cyclic citrullinated peptide in the routine clinical laboratory.

OBJECTIVE

To evaluate the performing technical and clinical characteristics of an automated system for routine measurement of anticyclic citrullinated peptide antibodies (aCCP), a new marker for rheumatoid arthritis (RA).

MATERIAL AND METHODS

Reproducibility, repeatability and linearity of aCCP, as measured by an automated fluorescent enzyme immunoassay (FEIA/Phadia), were evaluated and compared with the performance of a manual ELISA technique (Axis Shield Diagnostics). Clinical verification of both methods included estimation of sensitivity in RA patients (n = 42) and specificity in well-characterized non-RA autoimmune disease controls (n = 49) and healthy subjects (n = 39).

RESULTS

Precision studies showed a coefficient of variation between 4.9 % and 10 % for the FEIA technique and between 6.35% and 19% for the ELISA technique. Both systems showed good linear response. Sensitivity of aCCP for RA was 74% for FEIA and 79% for ELISA. Specificity was 100% for both methods, as calculated for healthy subjects. For non-RA-diseased controls, specificities of 98% and 94% were obtained for FEIA and ELISA, respectively. Both methods were concordant in 97% of cases. Increasing the cut-off for the ELISA system from >5 U/mL to >11 U/mL resulted in lower sensitivity (71.4%) but higher specificity (98.0%), i.e. improved discriminating power between RA and non-RA and 100% agreement between both methods.

CONCLUSION

Automated FEIA measurement of aCCP in the routine clinical laboratory improves imprecision compared to the manual ELISA. Our preliminary results suggest that an increase in cut-off for the ELISA can improve specificity to RA from 94% to 98 %.