“Physicians should recognize that C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are affected by obesity in patients with and without rheumatoid arthritis, especially in women,” Dr. Michael D. George from the University of Pennsylvania in Philadelphia told Reuters Health by email.
CRP and ESR are commonly used in the diagnosis and management of rheumatoid arthritis. In the general population, higher levels of CRP have been linked to greater body mass index (BMI) and adiposity, particularly among women. Elevated ESR has also been associated with higher BMI and adiposity in the general population.
Dr. George and colleagues evaluated associations between BMI and inflammatory markers in two groups of RA patients: the “Body Composition” cohort of 451 patients and the VA RheumatoidArthritis (VARA) registry cohort of 1652 patients. They derived their control group from the National Health and Nutrition Examination Survey (NHANES).
In both RA cohorts and in the general population, BMI was positively associated with CRP and ESR among women, especially among those who were severely obese (BMI of 35 or higher).
Among men in the general population, BMI was also positively associated with CRP and ESR, according to the April 10th Arthritis Care and Research online report.
Among men with RA, however, BMI was not associated with CRP or ESR, except that underweight men had significantly higher CRP and ESR than normal-weight men. In the VARA cohort, normal-weight men had higher CRP and ESR than men who were overweight or obese.
In women, CRP and ESR were positively associated with fat mass (but not lean mass), whereas neither biomarker was associated with fat or lean mass in men.
Based on these findings, women with severe obesity would be expected to have DAS28-CRP scores 0.29 point higher in the Body Composition group and 0.15 point higher in the VARA group. If their CRP levels were corrected to what would be expected for normal-weight individuals, 9.8% of DAS28 measurements in the Body Composition group and 11.4% of DAS28 measurements in the VARA group among severely obese women would be recategorized to lower disease activity categories.
“The increase in inflammatory markers seemed to be directly related to obesity and entirely independent of rheumatoid arthritis,” Dr. George said.
“Physicians should recognize that patients with obesity, especially severe obesity, may have modest elevations of CRP or ESR just because of their obesity,” he said. “For example, if a patient with obesity has joint pain that seems to be non-inflammatory based on history and exam but mild elevations in CRP, her physician should consider that the CRP elevation may be from obesity. Similarly, if a patient with rheumatoid arthritis who is obese is feeling well on therapy but CRP remains elevated, obesity may well explain the results and increasing therapy is probably not necessary.”