Performance characteristics of anti-cyclic citrullinated peptide and rheumatoid factor tests in rheumatoid arthritis and undifferentiated arthritis at Kenyatta National Hospital

Abstract

Background: The rheumatoid factor (RF) test has been the main serological test for diagnosis of rheumatoid arthritis. Reports of it’s low sensitivity and specificity led to the introduction of anti cyclic citrullinated peptide (anti CCP) test, which was added to the diagnostic criteria. The analytical method and cost of the anti CCP test limits its availability in resource constrained environments. Objective: To determine the analytical performance characteristics of anti CCP in patients with rheumatoid arthritis (RA) and undiffentiated arthritis (UA), and compare with those of RF. Design: Cross-sectional study. Methodology: The study subjects comprised 64 RA and 31 UA patients. Serum anti CCP was measured using an automated immunoassay and 3rd generation anti-CCP test. RF was determined using a qualitative particle agglutination method. Manufacturer cut-offs were used for interpretation of results. Sensitivity, specificity, negative and positive predictive values were calculated and compared, for anti-CCP and RF tests. Results: Anti CCP showed a higher sensitivity than RF (62.5% versus 50%). Specificity was however higher with RF (90.3%) than anti-CCP (83.9%). RF also had a slightly higher positive predictive value (91.4%) than anti-CCP (88.9%). Combining RF and anti-CCP tests led to a slightly higher sensitivity and negative predictive values than those obtained with RF alone but not specificity or positive predictive values. Conclusion: Although the anti CCP test has shown better sensitivity than RF in RA, there was slightly higher specificity and positive predictive value with RF compared with anti- CCP. The findings show that the latex RF test is an effective test for initial evaluation of patients with arthritis