Background The low, fluctuating levels of DNA characteristic of occult hepatitis B infection make its detection by nucleic acid testing (NAT) a challenge.
Methods Four year’s routine use of the Ultrio and Ultrio Plus assays in blood donations in New Zealand was analysed.
Results 0·09% of donations tested with Ultrio and Ultrio Plus assays showed reactivity in the multiplex assay, but non-reactivity in all three discriminatory assays and relevant mandatory serological assays (anti-HIV, anti-HCV, HBsAg). These donations were more likely to be anti-HBc reactive (Ultrio, 13%; Ultrio Plus, 57%; random donors, 6·8%). Thirty-four per cent of these anti-HBc-reactive donations were also reactive in either an alternate NAT assay or on repeat multiplex testing. Thirteen per cent of the donors of the discriminatory-negative, anti-HBc-reactive donations who had given other Ultrio- or Ultrio Plus-tested donations had at least one other multiplex reactive donation.
Conclusion These findings suggest that their HBV DNA levels are around the assay’s limit of detection, that false reactivity cannot be presumed when a donor fails to discriminate and that caution should be applied when deciding whether to continue accepting donations from such donors.