Cost-effectiveness of thiopurine methyltransferase genotype screening in patients about to commence azathioprine therapy for treatment of inflammatory bowel disease

Background: Azathioprine is a useful agent in the management of inflammatory bowel disease. Its use is limited by its side-effect profile. Marrow toxicity occurs in approximately 3.2% of patients and is known to be associated with diminished thiopurine methyltransferase enzyme activity resulting from genetic polymorphisms. Aim: To evaluate the cost-effectiveness of screening for thiopurine methyltransferase gene polymorphisms prior to initiation of azathioprine therapy. Methods: Analysis of the literature was undertaken to calculate the expected frequency of leucopenia and its relationship with thiopurine methyltransferase polymorphisms in a model of theoretical inflammatory bowel disease patients. Decision analysis was then applied to assess the cost of a pre-treatment genotyping strategy, taking account of direct costs and cost per life-year saved. Results: In 1000 inflammatory bowel disease patients treated with azathioprine, 32 will develop myelosuppression and one will die because of this. Of those who develop myelosuppression during azathioprine therapy, 32% are attributable to lower thiopurine methyltransferase activity. Pre-treatment genotyping costs pound347 per life-year saved for a 30 year old and pound817 per life-year saved for a 60 year old. This compares favourably with other health care technologies. Conclusion: The use of pre-treatment screening for thiopurine methyltransferase polymorphisms in inflammatory bowel disease patients commencing azathioprine therapy represents good value for money.