The research, which will be presented at the British Society for Rheumatology’s conference Rheumatology 2014, showed that of 64,000 patients undergoing rheumatoid factor testing in primary care, 1,800 were diagnosed with rheumatoid arthritis within two years. Of those, only 1,000 had had a positive result from the test.
Rheumatoid factor (RF) testing is typically used during patient assessments in specialist rheumatology departments. But 70% of RF tests take place in primary care where they may be used in referral decisions for patients with possible early rheumatoid arthritis. Here false negative results can have serious implications for referral times.
Rheumatoid factor is an antibody present in the blood of most, but not all patients with rheumatoid arthritis. A positive result supports the diagnosis, when clinical features are present. However, a negative RF result does not exclude this diagnosis.
The study, led by researchers from the University of Oxford and the University of Bath, used information from the Clinical Practice Research Datalink, a large UK primary care database. It found that of 64,000 patients tested with the RF test between 2000-2008, 1,800 were diagnosed with rheumatoid arthritis within two years. Of this group, 1,000 showed a positive RF test result and 800 showed a negative result, suggesting a prevalence of false negative results when the test is used in primary care.
Patients whose RF test was negative were not referred as promptly as those with a positive test. Their referral was typically 45 days later, generally taking 67 days. When treatment is not given within a 12-week window of opportunity following the disease onset it is more likely that there will be subsequent damage to joints and other organs, reduced function and lower likelihood of disease remission.
Lead researcher Anne Miller said: “It is important that rheumatoid factor tests are not used to rule out possible rheumatoid arthritis in primary care, and that patients with symptoms suggestive of inflammatory arthritis are referred for specialist assessment without delay.”
President of the British Society for Rheumatology, Dr Chris Deighton, said: “It is important to address all components of delay to people with early RA getting onto disease-modifying medication. This involves raising the profile of early inflammatory arthritis through campaigns like Simple Tasks, so that people do not delay seeing their GPs, and also that GPs realise that the diagnosis of early inflammatory arthritis is largely a clinical one, relying on symptoms and signs of inflammation, rather than tests which may be misleading.”
The research “A negative rheumatoid factor in primary care delays referral of patients with rheumatoid arthritis” will be presented at Rheumatology 2014 as an oral abstract.