NUDT15 R139C was comfirmed to be associated with thiopurine-induced leukopenia inflammatory bowel disease (IBD) cohort.The present study aim to explor the following questions:can optimizing thiopurine dose by NUDT15 genotype reduce thiopurine-induced leucopenia?What is the influence of this optimizing strategy on clinical outcome?Thus,we conduct a randomised controlled study.Subject in the conventional group detect NUDT15 genotype before thiopurine use and optimise dosage according to the genotype.While the subjects in the control group follow the conventional monitor strategy.The primary endpoint was the rate of leukopenia.The secondary endopoint was the efficacy of thiopurine.The follow up duration was 1 year.