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Abacavir, a human immunodeficiency virus-1 (HIV-1) nucleoside-analogue reverse transcriptase inhibitor, causes severe hypersensitivity in 4–8% of patients. HLA B*5701 is a known genetic risk factor for abacavir hypersensitivity in Caucasians. Our aim was to confirm the presence of this genetic factor in our patients, and to determine whether genotyping for HLA B*5701 would be a cost-effective use of healthcare resources.Patients with and without abacavir hypersensitivity were identified from a UK HIV clinic. Patients were genotyped for HLA B*5701, and pooled data used for calculation of test characteristics. The cost-effectiveness analysis incorporated the cost of testing, cost of treating abacavir hypersensitivity, and the cost and selection of alternative antiretroviral regimens. A probabilistic decision analytic model (comparing testing versus no testing) was formulated and Monte Carlo simulations performed.Of the abacavir hypersensitive patients, six (46%) were HLA B*5701 positive, compared to five (10%) of the non-hypersensitive patients (odds ratio 7.9 [95% confidence intervals 1.5–41.4], P = 0.006). Pooling of our data on HLA B*5701 with published data resulted in a pooled odds ratio of 29 (95% CI 6.4–132.3; P< 0.0001). The cost-effectiveness model demonstrated that depending on the choice of comparator, routine testing for HLA B*5701 ranged from being a dominant strategy (less expensive and more beneficial than not testing) to an incremental cost-effectiveness ratio (versus no testing) of €22 811 per hypersensitivity reaction avoided.Abacavir hypersensitivity is associated with HLA B*5701, and pre-prescription pharmacogenetic testing for this appears to be a cost-effective use of healthcare resources.