Anti-cyclic citrullinated peptide (CCP) antibodies and rheumatoid factor (RF) are recommended screening tests for rheumatoid arthritis.1 In a meta-analysis,2 the sensitivity of anti-CCP (67%) for diagnosing rheumatoid arthritis was comparable to the sensitivity of RF (69%).2 The specificity of anti-CCP for rheumatoid arthritis (95%) was higher than the specificity of RF (85%).2 Consequently, the positive likelihood ratio was higher for anti-CCP (12.46) than for RF (4.86).2

Studies that addressed the clinical usefulness of anti-CCP used a single cut-off value and, hence, likelihood ratios were calculated based on a single cut-off. In the present letter, we illustrate how likelihood ratios for anti-CCP and RF …