In men with RA, BMI was not associated with CRP level. This finding differed from the general population in which BMI as a continuous variable was positively associated with CRP level in men. Men with RA and high BMIs did not have significantly higher CRP levels compared with normal-weight men. However in both RA cohorts, underweight men had significantly higher CRP levels than normal-weight men. “This inverse association between BMI and CRP level in men is an RA-specific phenomenon and not a direct causal effect of adiposity,” note the authors.
Additionally, ESR was only modestly associated with BMI in men in the general population, while ESR was not associated with BMI among men with RA in the BC cohort and was negatively associated with BMI in the VARA registry.
“The current study is the largest to address this issue and illustrates the effect of inflammatory markers in specific BMI categories,” write the authors. “The inclusion of a non-RA control population demonstrates the normal relationship between BMI and inflammatory markers as a reference. … The effect of obesity on the CRP level may alter its performance as a biomarker of disease activity in clinical trials and in practice. … Furthermore, because obesity may be expected to impact the reliability of other component measures of disease activity, clinicians may tend to rely more on objective measures, such as CRP, for diagnosis or to make treatment decisions.”
George MD, Giles JT, Katz PP, et al. Impact of obesity and adiposity on inflammatory markers in patients with rheumatoid arthritis. Arthritis Care Res (Hoboken). 2017 Dec;69(12): . doi: 10.1002/acr.23229.