Levels of plasma fibrinogen are elevated in well-controlled rheumatoid arthritis

Patients with RA have systemic inflammation and increased risk of cardiovascular (CV) events, including thrombosis. Levels of fibrinogen, a pro-thrombotic protein with predictive value for CV disease (CVD), are elevated during systemic inflammation. We compared circulating fibrinogen levels in patients with RA with healthy controls and evaluated the relationship with measures of disease activity.

Patients with RA and controls were recruited at the University of California, San Francisco (UCSF). Disease activity was evaluated using standard composite indices. Fibrinogen, ESR, serum CRP, acute-phase serum amyloid A and levels of selected cytokines were quantified.

A total of 105 RA patients and 62 controls were studied. Among patients with RA, disease activity ranged from quiescent to highly active disease. Circulating fibrinogen levels were significantly higher in RA than in controls [median (interquartile range) 466 (391-575) vs 367 (309-419) mg/dl, respectively, P < 0.0001]. This difference remained highly statistically significant after adjustment for demographic variables and BMI. Although fibrinogen correlated significantly with clinical measures of disease activity, significantly elevated levels were observed at low levels of activity, even in RA patients with no detectable swollen or tender joints. In multivariable models, ~ 80% of the increased fibrinogen in RA was accounted for by increases in CRP and ESR.

Circulating levels of fibrinogen are elevated in RA and correlated with markers of inflammation, but only modestly correlate with clinical assessments of disease activity. Even RA patients with excellent clinical disease control exhibit elevated levels compared with controls.