Hepatitis B vaccine as a cause of false positive hepatitis B surface antigen.

The hemodialysis unit at The Toronto Hospital routinely vaccinates its patients against hepatitis B using Engerix B Hepatitis B Vaccine (Recombinant). A new positive hepatitis B surface antigen (HBsAg) was flagged by the lab, but upon investigation it was discovered that the patient had received hepatitis vaccine two days earlier. The infectious diseases service was consulted and the case was referred to the microbiologist. Subsequent testing showed a conversion to negative antigen. We decided to test other patients who had just been vaccinated to see if we could replicate our results. Seven other patients were selected, and we found the incidence of false positive HBsAg to be 50%. The duration of the vaccine-induced positive HBsAg lasted no more than two weeks. Our results are compatible with the results found in the current literature.