Objectives Around 1% of the population test positive for anti-cyclic citrullinated peptide (anti-CCP) antibodies. This biomarker predicts the progression to rheumatoid arthritis (RA) but over a variable time frame. To increase its clinical relevance, this study sought to determine (1) if the proportion of anti-CCP-positive individuals could be enriched by case selection of people attending primary care with new non-specific musculoskeletal (MSK) symptoms but without clinical synovitis (CS) and (2) whether these individuals progress rapidly to inflammatory arthritis (IA), in particular RA.

Methods In this prospective cohort study, individuals aged ≥18 years with new non-specific MSK symptoms, without CS, were recruited from primary care in the UK. Anti-CCP-positive individuals were invited for follow-up in the rheumatology department, Leeds. Those who tested negative were sent questionnaires 12 months later.

Results 2028 individuals were recruited. Of these, 2.8% (57/2028) were anti-CCP positive, of whom 47% (27/57) developed IA – 24 RA, 1 undifferentiated IA (UIA), 2 polymyositis; 92.6% (25/27) within 12 months, median 1.8 months (IQR 1.0–4.3, range 0.3–16.1). Of the anti-CCP-negative individuals, 1.3% (20/1559) developed IA (1 UIA, 13 RA, 6 psoriatic arthritis); 75% (15/20) within 12 months. The relative risk for developing RA within 12 months in the anti-CCP-positive group was 66.8 (95% CI 32.2 to 138.4, p<0.001); for IA, it was 45.5 (95% CI 25.4 to 81.6, p<0.001).

Conclusions Selecting individuals with new non-specific MSK symptoms without CS enriched the prevalence of anti-CCP positivity to 2.8%. Those who tested positive had a high risk of rapidly developing RA. The cost-effectiveness of this approach will need to be determined.

Trial registration number NCT02012764.