Serological markers are thought to be useful in predicting which patients with early inflammatory arthritis (EIA) will progress to RA. The objective of this study is to determine the per cent RF and anti-CCP seroconversion in EIA patients at 1-5 years of follow-up: 80% of established RA is RF or CCP positive.
We conducted a systematic literature review of all English publications and recent abstracts from ACR and EULAR. Patients ≥16 years of age with at least one swollen joint and symptoms < 2 years were included.
Twelve publications met the criteria: 10 studies included data on RF, while only 5 addressed anti-CCP. Sample sizes ranged from 15 to 395 and follow-up was 6-60 months. There was marked heterogeneity between studies; therefore, results could not be pooled for a meta-analysis. Baseline RF and anti-CCP positivity was also highly variable: 8-55 and 4-45%, respectively. Seroconversion rates for EIA were 1.9-5.0% at up to 30 months follow-up for RF and 1.3-8.9% at up to 60 months follow-up for anti-CCP.
There is minimal change in RF or anti-CCP positivity up to 5 years of follow-up. Prevalence data for RF in established RA is significantly higher than the baseline values reported here. The low rates of seroconversion would suggest a lower prevalence in EIA and the reason for this difference remains unknown. It is unclear whether antibody-negative patients are more likely to remit and be lost to follow-up in established RA populations.