When evaluated by CXCL13 tertile analysis, the highest tertile had much higher IgA RF values than the first and second tertiles in the Dartmouth RA Cohort (third-tertile geometric mean (95% CI) 45.0 IU/ml (28.0 to 72.3), first- and second-tertile geometric mean (95% CI) 11.2 IU/ml (7.6 to 16.3); P < 0.0001) (Figure 4B). This evidence concerns the gene CXCL13 and rheumatoid arthritis.