Hepatitis A virus (HAV)

• Virus that causes an acute hepatitis illness that self-resolves.
• Can very rarely cause liver failure.
• Doesn’t cause chronic infection like hepatitis B and C.
• Life-long immunity develops after infection or vaccination.
• Very uncommonly acquired in NZ unless known outbreak e.g. related to imported frozen berries. More common if recent history of overseas travel.

HAV is related to enteroviruses and spreads by faecal-oral transmission. Not considered a ‘blood-borne virus’ like hepatitis B and C.

Test people with acute hepatitis that isn’t due to another cause e.g. medications, alcohol.

• Don’t test people with chronic or low-level (<200) elevations in ALT/AST.
• If testing for immunity is required, this should be stated clearly on the request form.
• Mimics to consider in patients with hepatitis: hepatitis B and C, HIV, syphilis

Request Hep A serology, but must specify reason for test (immunity vs infection)

Hepatitis A total antibody detects both IgM and IgG antibodies and is the first test that is performed.

• Excellent sensitivity – a negative result excludes acute or past infection, as it means there is no detectable IgM or IgG.
• A positive result can be due to the presence of IgG, IgM or both.
  • In well patients where evidence of immunity is required, this is assumed to be IgG, which indicates immunity due to past infection or vaccination.
  • In patients with acute hepatitis, the laboratory will usually add on IgM testing.

Hepatitis A IgM is a marker of acute infection, and is detectable from time of symptom onset, but can persist for many months.

• Excellent sensitivity – a negative result makes acute infection very unlikely
• Moderate specificity – a positive result is supportive, but not confirmatory, as false positives due to cross reactions can occur.

Hepatitis A PCR

• This is usually performed on stool, but sometimes can be performed on blood also.
• Has excellent specificity, so can confirm hepatitis A in patients with a positive IgM.
• There is limited laboratory capacity to perform this test currently, so it is generally reserved for Public Health investigations.