ERFE and chronic kidney disease: In both cohorts, serum levels of ERFE had a left skewed distribution with a median value of 4.5 ng/mL and a wide range (from 1.6 to 140.4 ng/mL; mean value of 7.8 ±10.5 ng/mL) in HD patients, and a median of 1.6 ng/mL and a similarly wide range (from 1.6 to 127.8 ng/mL; mean of 3.4 ± 7.5 ng/mL) in CKD patients with no difference among sexes (HD cohort (males: median 4.47 ng/mL and females: median 4.69 ng/mL; p = 0.29); CKD cohort (males: median 1.65 ng/mL and females: median 1.62 ng/mL; p = 0.92)) (Figure S1).