Hepatitis A Serology

Diagnostic Use

Hepatitis A virus (HAV) is a ss RNA virus belonging to the family Picornaviridae.

Hepatitis A is commonly transmitted via the faecal/oral route and has an incubation period of 3-6 weeks. It occurs throughout the year but tends to peak in Autumn. It usually occurs through intra-household or sexual contact in conditions of poor personal hygiene or inadequate sanitation. Individuals most at risk for contracting the disease include (a) patients and staff in custodial institutions (b) those in close personal contact with infected persons (c) travellers to areas of endemic disease (d) children in day care centres (e)male homosexuals and (f) IV drug users. Clinical infection is usually abrupt in onset with symptomatic disease increasing with increasing age.

After an average incubation of 28 days, there is a rapid onset of symptoms (fever, abdominal pain, RUQ pain, pale stools, dark urine and jaundice) which persist for 1-2 weeks. HAV can be detected in faeces prior to and for approximately 1-2 weeks after symptom onset. Most adult cases (80%) are symptomatic however, there is a very high (90%) asymptomatic rate in children. The total antibody response commences shortly after symptom onset.

Complications are uncommon and there is no chronic carriage. The mortality rate in icteric cases is < 0.5% overall.

Positive anti-HAV (IgM) – indicates current or recent Hepatitis A infection

Anti-HAV IgG in the absence of IgM indicates past infection or seroconversion post vaccination. Confirms immunity to Hepatitis A. Roche Laboratories state that the assay cut-off (1.0) was standardised against the 20 IU/L considered as the quantitative level for HAV immunity.

Patients are infectious during the incubation period and for approximately one week after the development of jaundice.

Diagnosis of acute infection is by the detection of anti-HAV IgM antibodies.

Hepatitis A is a notifiable disease and it is important that cases with acute infection be notified promptly so that immunoprophylaxis can be considered for contacts.
References

1. Roche Laboratories anti-HAV IFU