When including only IL-6 levels of 20 pg/ml or lower, the correlation for SLE was lost (r = 0.18, P = 0.29), whereas the correlation for RA was maintained (r = 0.38, P = 0.04) (Supplementary Fig. S2, available at Rheumatology online). Here, IL6 is linked to systemic lupus erythematosus.