COST-EFFECTIVENESS ANALYSIS OF HLA-B*5801 TESTING IN PREVENTING ALLOPURINOL-INDUCED SJS/TEN IN THAILAND

Purpose: Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), caused by allopurinol therapy, are strongly associated with the human leukocyte antigen (HLA), HLA-B*5801. Identification of HLA-B*5801 genotype before prescribing allopurinol offers the possibility of avoiding this drug in individuals with such susceptibility and preventing allopurinol-induced SJS/TEN. As there is a paucity of evidence about economic value of such testing, this study aims to determine the cost-effectiveness of genetic testing for HLA-B*5801 compared with usual care (no genetic testing) before allopurinol administration in Thailand.

Method: A decision analytical model was used to estimate life year costs and outcomes represented as quality adjusted life years gained (QALY). The use of Markov model is needed to reflect long-term outcomes because some surviving SJS/TEN patients may suffer from long-term sequelae. The model was populated with relevant information of the association between gene and allopurinol-induced SJS/TEN, test characteristics, costs, and epidemiologic data for Thailand from a societal perspective. Input data were obtained from the literature and a retrospective database analysis. The results were expressed as incremental cost per quality-adjusted life years gained (QALY). A base-case analysis was performed for patients at age 30 from the societal perspective. A series of sensitivity analyses including threshold, scenario, one-way, and probabilistic sensitivity analyses were constructed to explore the robustness of the findings. 

Result: Based on a hypothetical cohort of 1,000 patients, the incremental total cost was 923,919 THB and incremental QALY was 4.65 with an ICER of 198,486 THB (USD 6,403) per QALY. Genetic testing for HLA-B*5801 before allopurinol administration was not considered a cost-effective intervention, based on a standard cost-effectiveness threshold of 160,000 THB/QALY in Thailand. However, when the cost of genetic testing was less than 822 THB (USD 26.5), the test becomes cost-effective at the societal willingness-to-pay level of 160,000 THB (USD 5,161)/QALY.

Conclusion: The genetic testing for HLA-B*5801 before allopurinol administration might not be considered as a cost-effective intervention. However, consideration of other factors including ethical, legal, and social implications is needed in order to make an informed policy decision making.