HLA-B and toxic epidermal necrolysis: As mentioned, HLA-B*5801 haplotype is the strongest risk factor for allopurinol-induced SCARs. Screening for HLA-B*5801 is beneficial in populations with high rates of allopurinol-induced toxic epidermal necrolysis/SJS, especially in populations with a higher frequency of the allele (≥ 5%) [92].