Introduction:
Obesity is known to be associated with elevated levels of inflammatory markers. The aim of the study was to assess the confounding effect of obesity on the levels of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in patients with rheumatoid arthritis (RA) in low disease activity state or remission as indicated by clinical disease activity index (CDAI).

Material and methods:
Adult RA patients with CDAI less than 10 were divided into two groups: obese and non-obese, based on body mass index. Relevant exclusions were applied to eliminate causes of raised inflammatory markers other than obesity. The difference of CRP and ESR levels between the obese and non-obese groups was analyzed.

Results:
Obese patients with RA (n = 85) had higher CRP and ESR than non-obese patients (n = 66) (p-values 0.008 and 0.000005, respectively). In addition, obese females with RA had significantly higher CRP and ESR as compared to non-obese females. However, the difference was not significant in males. Twenty-one obese (24.7%) and two non-obese RA patients (3%) had elevated CRP (difference of approximately 22% [24.7 minus 3]). Forty obese (47%) and 16 non-obese RA patients (24.2%) had elevated ESR (difference of approximately 23% [47 minus 24.2]). Thus, obesity was the attributable cause of falsely elevated CRP and ESR in 22% and 23% of patients, respectively.

Conclusions:
About one-fifth of patients with RA, who are actually in low disease activity, may have elevated inflammatory markers, primarily because of obesity. Therefore, elevated CRP and ESR in obese patients with RA should be interpreted with caution because it may lead to unnecessary overtreatment.