Diagnostic utility of anti-cyclic citrullinated peptide antibodies for rheumatoid arthritis in patients with active lung tuberculosis

This study was intended to evaluate the utility of anti-cyclic citrullinated peptide antibodies (second generation, anti-CCP2) as a diagnostic marker for rheumatoid arthritis (RA) in patients with active tuberculosis. Among 89 patients with active tuberculosis, anti-CCP2 was detected in six (6.7%), and three of these (3.4%) were strongly positive for anti-CCP2. The positive rate of anti-CCP2 in patients with newly diagnosed RA was 82.1% (87 of 106 cases), while the rate in healthy control subjects was 0.4% (one of 237 individuals). The mean level of anti-CCP2 among the RA group was 159.3 U/ml, which was significantly higher than both that among the tuberculosis group (15.4 U/ml) and that among the healthy controls (0.7 U/ml). IgM rheumatoid factor (RF) was detected in 16 patients from the tuberculosis group (18.0%) with a mean serum level of 18.6 IU/ml and in 77 patients of the RA group (72.6%) with a mean level of 164.0 IU/ml. Only two cases in the tuberculosis group were positive for both anti-CCP2 and IgM RF. These observations show that measurement of anti-CCP2 seems to be a reliable serological tool for identifying early RA in patients with active tuberculosis.