This practical procedure indicates that in patients with HLA-A (or -B) allele mismatch, HLA-B (or -A) allele is more likely to be matched, while in patients with HLA-C mismatch, the disparity of HLA-A and -B alleles are determined randomly (independent of HLA-C mismatch status), resulting in larger number of overall HLA class I mismatch alleles in the patients with HLA-C mismatches; this selection bias may contribute to a higher incidence of viral infections in those with HLA-C mismatches. Here, HLA-B is linked to viral infectious disease.