Hepatitis B virus

• Hepatitis B is now uncommonly acquired in NZ, mostly due to routine immunisation.
• People born in countries where perinatal or childhood acquisition has still occurred more recently e.g. the Pacific, SE Asia have a higher likelihood of HBV infection.
• Long-term active infection carries a risk of cirrhosis and hepatocellular carcinoma.

• HBV ‘hides’ its DNA in the nucleus of liver cells.
• People whose surface antigen becomes negative are often described as having ‘past’ or ‘cleared’ infection. However, this ‘hidden’ DNA persists in these people, meaning the infection can return if they become significantly immune compromised.

Request serology, but need to specify which from below:

Hep B surface antigen (sAg, HBsAg) demonstrates active replication of virus in the liver

• Request this to diagnose active infection e.g. investigation of deranged LFTs.
• The terms ‘active’ vs ‘past’/‘cleared’ relate to HBsAg being present or absent.

Hep B surface antibody (anti-HBs, HBsAb) demonstrates immunity to HBV if the level is >10. This can be due to past infection or vaccination.

• Request this if demonstration of immunity is required e.g. pre-employment.
• People who have ever had a level >10 are considered immune, even if the anti-HBs level wanes over time.

Hep B core antibody (anti-HBc, anti-core, HBcAb) demonstrates infection at some point

• Request this if need to know if have ever been infected e.g. before immune suppression
• If combined with:
  • detectable HBsAg = current active infection
  • non-detectable HBsAg = ‘past’/’cleared’ infection

Hep B core IgM antibody is a subset of core antibody and is produced in acute infection.

• e.g. investigation of patient with markedly deranged LFTs and positive HBsAg
• Many labs will add this on automatically if new diagnosis of HBV and deranged LFTs
• Specificity is only moderate – a positive test doesn’t necessarily confirm acute HBV infection and can be due to other things.

HBV DNA (HBV viral load, HBV PCR)

• This is used for monitoring of patients with known HBV infection and is not part of the standard initial diagnostic pathway for HBV.

Acute hepatitis B is a notifiable disease.