Nitric oxide production is increased in patients with rheumatoid arthritis but does not correlate with laboratory parameters of disease activity

Background: To investigate whether nitric oxide (NO) production correlates with laboratory parameters of disease activity in patients with rheumatoid arthritis (RA), we measured serum nitrates and nitrites (NOx) concentrations, rheumatoid factor (RF), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and serum iron markers in 115 RA patients. Methods: Serum NOx concentrations were determined after reduction of nitrates to nitrites using the Griess reaction. Serum transferrin receptor (sTfR) and serum ferritin were assayed using an enzyme immunoassay and a chemiluminescence method. Correlation coefficients of CRP, ESR, and RF vs. NOx concentrations were assessed. Results: Serum NOx concentrations averaged 208.3±126.8 μmol/l in RA patients without iron deficiency (n=72) and 267.9±148.4 μmol/l in RA patients with iron deficiency (n=43), which were significantly higher than those of healthy controls (32.7±14.3 μmol/l, p