Key result
Primary care RF testing yields a ~21% positive predictive value for diagnosing rheumatoid arthritis.
Why the study?
The diagnostic accuracy of rheumatoid factor as a test for rheumatoid arthritis in primary care and its impact on referral times was not well established.
What is the diagnostic accuracy of rheumatoid factor testing for rheumatoid arthritis in primary care?
Observational (n=62,436)
Yes
What is the diagnostic accuracy of rheumatoid factor testing for rheumatoid arthritis in primary care?
Effect estimate: Positive LR 9.5 (95% CI 9.0-10.0)
Absolute Event Rate: 21.4% vs 1.3%
In primary care, rheumatoid factor testing has high specificity but low sensitivity for rheumatoid arthritis, meaning a positive test is helpful but a negative test performs poorly in excluding the disease and may delay referral.
RF testing supports RA suspicion on positives in primary care but negatives warrant caution; leaves open refined referral strategies in real-world diagnostics.
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.
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Miller et al. (2015) conducted an observational in Rheumatoid arthritis (n=62,436). Rheumatoid factor (RF) testing vs. Negative RF test was evaluated on Diagnosis of rheumatoid arthritis within 2 years (Positive LR 9.5, 95% CI 9.0-10.0). Rheumatoid factor testing in primary care had a sensitivity of 57.8% and specificity of 93.9% for diagnosing rheumatoid arthritis, with a positive predictive value of 21.4%.
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