Serology

There is a rise in serum transaminases 22-40 days after exposure. (1)

Serum antibody to HAV appears as the stool becomes negative for virus:

• serum IgM anti-HAV (2)
  • implies recent infection
  • detectable about 3 weeks after exposure and increases in titre over 4–6 weeks, it persists for 2-6 months (rarely for up to one year) in low titre then declines to non-detectable levels
  • negative tests should be repeated if taken <5 days after the onset of symptoms to exclude a false-negative result
  • when the test result is reactive but probable non-specific IgM reactivity, repeat the test
  • false positive IgM are more common in the elderly and should be interpreted with caution (since they are likely to have had hepatitis A in childhood)
• serum IgG anti-HAV
  • persists for many years (usually lifelong)
  • probably conveys immunity to further infection with HAV (1)

Other investigations include: (3)

• serum/plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels – 500-10,000 i.u./l
• bilirubin – up to 500 micromoles/litre
• alkaline phosphatase levels
• prothrombin time – if prolonged for more than 5 seconds suggests developing hepatic decompensation and severe infection.

Reference:

1. Castaneda D, Gonzalez AJ, Alomari M, et al; From hepatitis A to E: A critical review of viral hepatitis. World J Gastroenterol. 2021 Apr 28;27(16):1691-1715.
2. Nelson NP, Weng MK, Hofmeister MG, et al. Prevention of hepatitis A virus infection in the United States: recommendations of the Advisory Committee on Immunization Practices, 2020. MMWR Recomm Rep. 2020 Jul 3;69(5):1-38.
3. United Kingdom National Guideline on the Management of the viral hepatitides A, B and C; British Association for Sexual Health and HIV (2015)