Test Details: Tacrolimus is an immunosuppressant that is used worldwide for the prevention of graft rejection in kidney transplant recipients. Cytochrome P450 (CYP) 3A4 and 3A5 made by CYP3A5 gene are involved in metabolism of tacrolimus. Determination of the CYP3A5 genotype is helpful in the determination of adequate immunosuppressive treatment and in lowering toxicity by predicting the doses of tacrolimus required for the induction and maintenance phases in kidney transplant recipients.