Is rheumatoid factor still a superior test for the diagnosis of rheumatoid arthritis?

The diagnosis of rheumatoid arthritis (RA) is based primarily on the 1987 revised American College of Rheumatology criteria for RA, which considers mainly the clinical symptoms. But typical clinical symptoms of RA are not manifested completely in early disease course. On the other hand, appreciable advantages have been made in the therapeutic strategy of RA in the last decade and highly effective disease-modifying anti-rheumatic drugs are available now for the control of RA. The treatment strategy for the control of early RA is aggressive. Thus, a highly specific and early diagnostic marker is needed for the detection of RA. Our study is an attempt to see the role of anti-CCP2 antibody (claimed to be highly specific and early diagnostic tool) in the diagnosis of RA. We studied 119 cases of RA in terms of clinical symptoms, disease duration and various autoantibody [including rheumatoid factor (RF), anti-CCP2 antibody, antinuclear antibody, anti-dsDNA] and C-reactive protein status. All the tests were also performed in 26 age and sex-matched healthy controls. Estimation of antibodies was done by quantitative ELISA. IgM RF was positive in 47.89% cases (p value = 0.000), followed by IgG RF (42.01%, p = 0.000) and IgA RF (36.97%, p = 0.000). RF was positive in 64.7% RA cases (p value = 0.000) when all three isotypes were tested together. RF was also detected in one healthy control. In 92 cases, anti-CCP2 Ab was done, hence other data were analyzed further in 92 cases only. Anti-CCP2 Ab was positive (cut-off = 15.0 U/ml) in only 50% RA patients but none of the healthy controls was positive for it. Swelling of joints was seen in 82.6% anti-CCP2 Ab positive cases (p value = 0.092) when compared with anti-CCP2 Ab negative cases (67.4%) while among RF positive cases, only 65.4% ((p value = 0.010) cases had swelling of joints. Out of 39 RA cases presenting with disease duration less than 1 year, only 48.71% patients were anti-CCP2 Ab positive while RF was positive in 61.53% patients. Utility of various combined autoantibody tests revealed that if one does all isotypes of RF (IgG, IgA and IgM) only, then 64.7% RA cases can be diagnosed and if anti-CCP2 Ab is added to it, the sensitivity increases to 75.56%. Thus, our study concludes that anti-CCP2 Ab is not a sensitive test for the diagnosis of RA neither it is useful in early diagnosis of RA, but it increases the sensitivity if added with all RF isotypes.