tokens: HBsAg , anti - HBs , anti - HBc , and anti - HIV 1 / 2 were determined as part of routine diagnosis using Axsym assays ( Abbott Laboratories , North Chicago , IL ). Serum samples were PCR amplified with HBV reverse transcriptase ( RT ) primers , followed by direct sequencing across the tyrosine - methionine - aspartate - aspartate ( YMDD ) motif of the major catalytic region in the C domain of the HBV RT enzyme .