Objective: To examine the rates of and risk factors for neutropenia together with the dynamics of neutrophil and other white cell subset counts in a cohort of patients treated with a tumor necrosis factor (TNF) inhibitor for inflammatory arthritis.
Methods: We performed a retrospective cohort study examining the association between baseline demographics, clinical features, medications used, and development of neutropenia, and behavior of neutrophil and other white cell subset counts during TNF inhibitor therapy.
Results: In 367 patients (298 [81.2%] with rheumatoid arthritis, 38 [10.4%] with ankylosing spondylitis, and 31 [8.4%] with psoriatic arthritis), 69 (18.8%) had at least one episode of neutropenia (<2.0 x 10(9)/liter) during TNF inhibitor therapy, and of these, 6% developed serious infections secondary to neutropenia. There was no significant difference in disease, demographic, or drug variables between patients with and without neutropenia. However, patients with neutropenia had significantly lower baseline neutrophil counts (4.2 x 10(9)/liter; 95% confidence interval [95% CI] 3.8, 4.6 versus 6.2 x 10(9)/liter; 95% CI 6.0, 6.5), and a previous history of neutropenia while receiving disease-modifying antirheumatic drugs increased the risk while receiving TNF inhibitors (hazard ratio 2.97; 95% CI 1.69, 5.25). A significant drop in mean neutrophil count (1.12 x 10(9)/liter; 95% CI 0.92, 1.32) was observed after 2 weeks of TNF inhibitor therapy. Other white cell subsets tended to significantly increase.
Conclusion: TNF inhibitor therapy is associated with a significant reduction in peripheral blood neutrophil count, leading to 19% of patients becoming neutropenic. Risk of neutropenia is significantly higher in patients with a low baseline neutrophil count or previous history of neutropenia. We suggest that patients receiving TNF inhibitor therapy would benefit from regular complete blood cell count monitoring.