Diagnostic Value of the Antiperinuclear Factor by Indirect Immunofluorescence Method

Jung, Kyoung Yun; Kim, Sang Gyung; Suh, Hun Suk; Lee, Jin Bae; Kim, Chae Gi; Song, Yong Ho; Choe, Jung Yoon; Shin, Im Hee

Abstract

BACKGROUND: The antiperinuclear factor (APF) has been reported both as a diagnostic tool and as a prognostic marker for rheumatoid arthritis (RA). Our purpose is to study the diagnostic value of the APF, and to compare the detection method of the indirect immunofluorescence method (IIF) and the citrullinated cyclic peptides enzyme-linked immunosorbent assay (CCP-ELISA).
METHODS
A total of 131 patients were included in this study. The APF were measured with both the IIF and ELISA. The IIF and ELISA procedures were carried out following the kit's instructions. The medical records such as C-reactive protein (CRP), erythroid sedimentation rate (ESR), the Ritchie index and diagnosis were reviewed retrospectively. SPSS (version 10.0, SPSS inc., USA) was used for statistical analysis.
RESULTS
The patients were 94 with RA, 26 with osteoarthritis, 7 with fibromyalgia syndrome, and 3 with palindromic rheumatism, 2 with gout, 2 with systemic lupus erythematosus, 1 with Behcet's disease, and 7 with non specific rheumatic diseases. The sensitivity and the specificity of the APF test in patients with RA were 93%, and 81%, while those with the rheumatoid factor (RF) were 91% and 63% , suggesting the APF has a higher specificity than RF. The area under the curve of APF was 0.87 (95% confidence interval, 0.79 - 0.95), but RF was 0.77 (95% confidence interval, 0.67- 0.87). The kappa statistics between the two detection methods IIF and ELISA was 0.667 (P=0.000), indicating disagreement between these two methods. The detection sensitivety and specificity of APF-IIF were 89% and 73%, while those of ELISA were 80% and 73%. The area under the curve of APF-IIF was 0.82 (95% confidence interval, 0.72- 0.90), but CCP-ELISA was 0.77 (95% confidence interval, 0.67- 0.86). There was a statistically significant correlation between the APF grade and the clinical parameters such as RF (r=0.503, P=0.000), CRP (r=0.333, P=0.000) and ESR (r=0.261, P=0.003).
CONCLUSIONS
Taken together, the APF could play a role in diagnosing RA in addition to RF. APF-IIF showed a higher sensitivity than ELISA.