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OBJECTIVE: To investigate the diagnostic accuracy of RF as a test for RA in primary care and its impact on referral times using the Clinical Practice Research Datalink. METHODS: We identified all patients with a first RF test recorded in the Clinical Practice Research Datalink between 1 January 2000 and 31 December 2008 and those diagnosed with RA within 2 years of testing. We calculated likelihood ratios (LRs), sensitivity, specificity and predictive values of RF for a diagnosis of RA. We compared time to hospital referral in those testing positive and negative using Kaplan-Meier failure curves and log-rank tests. RESULTS: Of 62 436 first RF tests, 4679 (7.5%) were positive. There were 1753 incident cases of RA, of which 57.8% were seropositive. The positive LR for RF was 9.5 (95% CI 9.0, 10.0) and the negative LR was 0.5 (95% CI 0.4, 0.5). Sensitivity and specificity were 57.8% (95% CI 55.4%, 60.1%) and 93.9% (95% CI 93.7%, 94.1%) and the positive predictive value and negative predictive value were 21.4% (95% CI 20.3%, 22.6%) and 98.7% (95% CI 98.6%, 98.8%), respectively. Median time to first hospital contact after the first RF test in those with seropositive vs seronegative results was 54 days (95% CI 49, 58) vs 150 (95% CI 147, 152). CONCLUSION: Only 2.8% of patients undergoing RF testing were diagnosed with RA, suggesting that RF is used to screen patients with musculoskeletal symptoms rather than those with more specific features of RA. A positive RF test may be helpful in diagnosing RA in primary care but performs badly in excluding RA and may delay referral.

Original publication




Journal article


Rheumatology (oxford)

Publication Date





1882 - 1889


primary care, rheumatoid arthritis, rheumatoid factor, sensitivity, specificity, Adult, Aged, Arthritis, Rheumatoid, Biomarkers, Databases, Factual, Female, Humans, Kaplan-Meier Estimate, Longitudinal Studies, Male, Middle Aged, Practice Patterns, Physicians', Predictive Value of Tests, Primary Health Care, Prognosis, Referral and Consultation, Retrospective Studies, Rheumatoid Factor, Risk Factors, Sensitivity and Specificity, United Kingdom