S100A8 and rheumatoid arthritis: Moreover, the S100A8 protein in sera was significantly more specific (AUC = 0.78, p = 0.006) in all RA patients than the CRP level (AUC = 0.63, p = 0.215), which also indicates that S100A8 was superior to CRP as a biomarker of high disease activity (Figure 5A).