PTPRC and rheumatoid arthritis: To test whether ct‐CD45 levels were directly linked to clinical parameters of RA patients, we performed linear regression analysis with levels of C‐reactive protein (Supporting Information Fig. 8A) and rheuma factor (Supporting Information Fig. 8B) as well as with the disease activity scores CDAI and DAS28 (Supporting Information Fig. 8C and D), but found no statistically significant correlation.