Haematological abnormalities in new onset rheumatoid arthritis and risk of common infections: a population-based study

Objectives: To describe the prevalence of haematological abnormalities in individuals with rheumatoid arthritis (RA) at the point of diagnosis in primary care, and the associations between haematological abnormalities, vaccinations and subsequent risk of common infections.

Methods: We studied 6,591 individuals with newly diagnosed RA between 2004 and 2016 inclusive using the UK Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) primary care database. The prevalence of haematological abnormalities at diagnosis (anaemia, neutropenia and lymphopenia) was established. Cox proportional hazards models were used to evaluate i) the association between each haematological abnormality and time to common infections; ii) the influence of vaccination status (influenza and pneumococcal vaccine) on time to common infections in individuals with RA, compared with a matched cohort of individuals without RA.

Results: Anaemia was common at RA diagnosis (16.1% of individuals), neutropenia (0.6%) and lymphopenia (1.4%) less so. Lymphopenia and anaemia were associated with increased infection risk (respective hazard ratios (HR) 1.18 (95%CI 1.08-1.29); HR 1.37 (95%CI 1.08-1.73)). There was no evidence of an association between neutropenia and infection risk (HR 0.94 (95%CI 0.60-1.47). Pneumonia was much more common in individuals with early RA compared with controls. Influenza vaccination was associated with reduced risk of influenza-like illness only for individuals with RA (HR 0.58 (95% CI 0.37-0.90).

Conclusion: At diagnosis, anaemia and lymphopenia, but not neutropenia, increase the risk of common infections in individuals with RA. Our data support the effectiveness of the influenza vaccination in individuals with RA.