CYP3A4 and chronic kidney disease: We showed the potential of 4β-OHC to 4α-OHC ratio for cross-sectional CYP3A phenotyping in healthy volunteers and CKD patients in this study, but the interindividual variability in 4β-OHC to 4α-OHC ratio was large within each group, although a significant difference was observed among three groups (Fig. 4).