Significance of anti-HBc only in blood donors: a serological and virological study after hepatitis B vaccination.

Background: Blood donors positive only for anti-HBc may have a resolved hepatitis B virus (HBV) infection, low grade chronic infection or infection with variant strains of HBV. We aimed to assess the significance of this serological pattern after hepatitis B vaccination in such cases.
Materials and Methods: Twenty-four anti-HBc only blood donors were vaccinated with the Engerix HBV vaccine and a serological and virological evaluation was performed before HBV vaccination and 7-10 days after each dose. Subjects were classified as non-responders if their anti-HBs levels stayed below 10 IU/L after full vaccination, while the response was considered secondary (anamnestic) if anti-HBs levels rose over 10 IU/L after the first vaccine dose, and primary if anti-HBs levels rose over 10 IU/L only after the second or third vaccine dose.
Results: Of the 21 fully evaluable donors, six had no response, eight showed a primary response and seven had an anamnestic response. One non-responder had transient positivity for HBV-DNA at low levels (12 IU/mL) with persistent negativity for HBsAg.
Discussion: Anti-HBc-only positive blood donors are a heterogeneous population including HBV naïve subjects with a likely false-positive anti-HBc reactivity, subjects with a resolved HBV infection, and subjects with persistent low-level HBV replication. The analysis of the anti-HBs response after a dose of HBV vaccine may help to distinguish among the different causes of the isolated anti-HBc positivity, thereby enabling proper counselling and potential readmission to blood donation.