The significance of 'anti-HBc only' in the clinical virology laboratory.

BACKGROUND: Isolated detection of hepatitis B core antibody (anti-HBc) in the absence of surface antigen (HBsAg) or antibody (anti-HBs) has been reported, particularly among individuals infected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV). The significance of this phenomenon is unknown and it is unclear whether all individuals with such serological pattern need further molecular investigations. OBJECTIVES: To determine the prevalence of 'anti-HBc only' in samples referred to a clinical virology laboratory and to evaluate its significance and possible mechanisms. STUDY DESIGN: Samples identified as anti-HBc positive (389/4359, 8.9%) during an 11-month period were investigated for HBsAg, anti-HBs, anti-HCV and anti-HIV. 'Anti-HBc only' samples were tested for HBV DNA using a nested qualitative PCR. Viral loads were measured in samples with detectable HBV DNA and the DNA sequences were analysed. RESULTS: Of 379 samples with detectable anti-HBc, 155 (40.9%) were 'anti-HBc only'. HBV DNA was detected in 6/151 (4%), all of which had a viral load <400 copies per ml. Anti-HIV was found in 50/151 (33.1%) and anti-HCV in 14/151 (9.3%). Of these, only one of the HIV infected patients had detectable HBV DNA. Phylogenetic analysis of the HBV surface gene from three patients showed a variety of genotypes (A, E and G). One sequence had a mutation in codon 144, which has previously been reported to give false negative HBsAg results. CONCLUSIONS: 'Anti-HBc only' is a common phenomenon in the clinical virology laboratory but only a small proportion of samples had detectable HBV DNA. The presence of HBsAg mutants with possible false negative HBsAg test result is of concern. Samples with 'anti-HBc only' could be used to monitor the emergence of these mutants.