title: The significance of 'anti-HBc only' in the clinical virology laboratory.
abstract: 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.
  
  
  OBJECTIVE
  To determine the prevalence of 'anti-HBc only' in samples referred to a clinical virology laboratory and to evaluate its significance and possible mechanisms.
  
  
  METHODS
  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.
authors.affiliation: Department of Biosciences, University of Westminster, London, UK
authors.forename: Fadel
authors.initials: F
authors.lastname: Alhababi
authors.forename: Talal A
authors.initials: TA
authors.lastname: Sallam
authors.forename: C Y William
authors.initials: CY
authors.lastname: Tong
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D004279:DNA, Viral / Q000097:blood; D005260:Female; D005838:Genotype; D006509:Hepatitis B / Q000097:blood / Q000175:diagnosis*; D006510:Hepatitis B Antibodies / Q000097:blood*; D006512:Hepatitis B Core Antigens / Q000276:immunology*; D006514:Hepatitis B Surface Antigens / Q000235:genetics; D006784:Hospitals, Teaching; D006786:Hospitals, Urban; D006801:Humans; D007755:Laboratories, Hospital / Q000592:standards*; D008131:London; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D016415:Sequence Alignment; D019562:Viral Load
chemical_list: D004279:DNA, Viral; D006510:Hepatitis B Antibodies; D006512:Hepatitis B Core Antigens; D006514:Hepatitis B Surface Antigens