CRP and rheumatoid arthritis: Furthermore, there is no standardized reference range or unit of measure for CRP values; these vary between laboratories [29]. In the RA synovium, there is an overabundance of pro-inflammatory cytokines that stimulate the production of CRP by the liver, thus making it an attractive candidate as a disease activity biomarker [30]. However, CRP measurement in RA is not foolproof.