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GPs should not rely on the rheumatoid factor (RF) test to rule out arthritis, experts have said, after research found it often misses cases of the disease and causes delays in diagnosis.

Rheumatoid arthritis patient referrals delayed by test results
Drs Kamal Mahtani & Tim Holt, Nuffield Department of Primary Care Health Sciences, University of Oxford

The study, led by researchers from the University of Oxford and the University of Bath, 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. 

The Rheumatoid Factor test may confuse GPs , who should rely more on clinical assessment than on blood tests in deciding whom to refer". - Dr Tim Holt (co-author), Nuffield Department of Primary Care Health Sciences, University of Oxford

Most RF tests take place in primary care and are used in referral decisions. However, RF antibodies are only detected in around eight out of 10 patients with arthritis and do not always show up in the early stages of the condition. 

The research “A negative rheumatoid factor in primary care delays referral of patients with rheumatoid arthritis” from Anne Miller, Alison L. Nightingale, Cormac J. Sammon, Kamal R. Mahtani, Tim Holt, Neil McHugh, Corinne S. de Vries, Raashid A. Luqmani will be presented at Rheumatology 2014 as an oral abstract.