Rheumatoid factor is an autoantibody used in the classification of rheumatoid arthritis. It can also be present in other inflammatory conditions and is seen in people without known inflammatory conditions. Some studies suggest that the prevalence of rheumatoid factor positivity in the general population increases with age and smoking status.1 2 As a consequence, merely being rheumatoid factor positive, without any symptoms, rarely prompts follow-up aimed at early identification of rheumatoid arthritis today.

In a linked research paper (doi:10.1136/bmj.e5244), Nielsen and colleagues investigated the long term risk of rheumatoid arthritis in the Danish general population according to titre of rheumatoid factor. They used national hospital registers to detect rheumatoid arthritis in a sample of the general population in whom plasma samples had been collected and frozen in 1981-83.3 Around 4.3% of the cohort were seropositive—a proportion generally comparable to other studies in non-rheumatoid arthritis populations.1 2 4 The authors reported that the risk …