Dear Editor,

The administration of the hepatitis B virus (HBV) vaccine to patients undergoing renal replacement therapy using the technique of haemodialysis is common in haemodialysis units, given that these patients are considered high risk. The vaccines used are made up of recombinant particles, which are mostly main surface proteins.1 The vaccine used in our hospital is Engerix-B which involves an intramuscular injection of 40 micrograms at the following times: 0, 1, 2 and 6 months; in nonresponsive patients, this is administered a second time.

The case of two patients who presented positive results for hepatitis B surface antigen (HbsAg) following vaccination is described here. The first case involves a 60-year-old woman who began renal replacement therapy (RRT) using the haemodialysis technique (HD) in April 2009 because of chronic kidney disease (CKD), secondary to  mesangiocapillary glomerulonephritis, and received the first monthly dose of the vaccine on 30 May 2009. The second case involves a 51-year-old woman who began RRT via HD in March 2009 because of CKD secondary to Wegener¿s granulomatosis and received the second monthly dose of the vaccine on 30 May 2009. Viral marker testing was carried out on 2 June 2009 in accordance with the protocol established in our hospital and both patients were HbsAg positive. Therefore, it was decided that they should be isolated and that all patients and staff in the unit should be tested for hepatitis B virus DNA and transaminases. The results were negative and both patients also presented negative results for HbsAg.

To summarise, in the cases presented, false positive results for HbsAg were observed following vaccination.2,3,4 The objective of describing these cases is to highlight the possibility of obtaining false positive results following vaccination and to remind others that serological tests should be carried out at least 2-3 weeks after vaccinations are administered.2,3,4