Diagnostic Performance of the Antifilaggrin Antibody in Rheumatoid Arthritis

Choi, Suk Woo; Lim, Mi Kyoung; Sheen, Dong Hyuk; Ihm, Chun Hwa; Shim, Seung Cheol

Abstract

BACKGROUNDS: Rheumatoid factor (RF) is common serological marker for the diagnosis of rheumatoid arthritis (RA), but its sensitivity and specificity are not satisfactory for the diagnosis of RA. Therefore, we investigated the diagnostic performance of a new antifilaggrin antibody test by enzyme linked immunosorbent assay (ELISA) in RA.
METHODS
Recombinant human filaggrin was deiminated in vitro by peptidylarginine deiminase and used as the coating antigen for ELISA. We performed the RF and the antifilaggrin antibody for 324 RA patients, 251 non-RA patients (rheumatic diseases other than RA), and 286 normal individuals and evaluated the sensitivities and specificities of RF and antifilaggrin antibody. Optimal cut off values were calculated as mean+2SD in 95% confidence interval except 3SD for 286 normal individuals. Optimal cut off values of antifilaggrin antibody and RF were 9.6 U/ml and 12 U/ml, respectively.
RESULTS
The sensitivities and specificities of antifilaggrin antibody were 44.8% and 89.2% at optimal cut off values. The sensitivity and specificity of RF were 75.0% and 83.3%. Combination of "antifilaggrin antibody and RF" showed significantly high specificity of 95.2% and that of "antifilaggrin antibody or RF" showed slightly high sensitivity of 79.3% at optimal cut off values. Antifilaggrin antibody was positive in 17.3% among 81 sero-negative RA patients.
CONCLUSION
We considered that antifilaggrin antibody could be used a supplementary test of RF for the diagnosis of RA, because "antifilaggrin antibody and RF" had higher diagnostic specificity than RF alone and antifilaggrin antibody test was easy, convenient ELISA method in performance.