Second, although direct evidence has previously been provided for the correlation between leukocyte expression and hepatic enzyme activities (as well as hepatic expression) of CYP1A2, CYP2C9, CYP2C19 and CYP3A4 [13], it should be validated for patients with end-stage renal disease. This evidence concerns the gene CYP2C9 and stage 5 chronic kidney disease.