Hepatitis A Virus Antibodies

Hepatitis A virus (HAV) is a small, 27 nm RNA virus that is the most common cause of hepatitis worldwide. It is primarily transmitted by the fecal-oral route after close contact with an infected person. It is acquired through ingestion of contaminated food or water. After decades of improved sanitation and hygiene and the introduction of HAV vaccination in 1995, the number of infections in the US declined from 31,032 to 1,398 cases per year between 1996 and 2011.  

However, HAV infections increased between 2016 and 2018. CDC received approximately 15,000 reports of HAV infections from US states and territories. The vast majority of these cases were associated with drug use and homelessness. Other infections in the US have occurred among  men who have sex with men (MSM). A small number of cases have been caused by consumption of imported HAV-contaminated food. 

Historically, genotype IA has been the most common genotype circulating in North and South America. HAV genotype IB has been predominant in the most recent outbreaks. Increasing numbers of genotype IIIA were also seen, which used to be rare in the United States.

HAV is generally a self-limited infection that does not have a chronic phase. Symptoms of hepatitis A infection include nausea, vomiting, abdominal pain, fever, jaundice, and pruritus. Hepatitis A infection is typically self-limited and does not lead to chronic liver disease or to a persistent carrier state. There is a 1% incidence of fulminant liver failure due to acute hepatitis A infection, predominantly in patients with underlying liver disease.

The incubation period is short, averaging 28 days and ranging from 15 to 45 days. Viral shedding in stool usually peaks 2 weeks prior to the development of symptoms. Prolonged viral shedding can occur in children. 

Symptoms of HAV infection are indistinguishable from other causes of viral hepatitis, so diagnosis must be established by serological testing. A positive result for anti-HAV IgM establishes the diagnosis of acute hepatitis A. Anti-HAV IgM is detectable at the time of symptom onset and can remain elevated for 3 to 12 months following infection. 

An indeterminate IgM result should be followed-up by repeat testing. 

A positive IgM anti-HAV test result in a person without symptoms of hepatitis A might indicate:

• Asymptomatic acute HAV infection
• Previous hepatitis A infection with prolonged presence of IgM anti-HAV
• False positive test result 

Anti-HAV IgG antibodies become detectable early in the convalescent phase of an acute infection or after HAV vaccination. HAV IgG is detectable for decades following infection or vaccination. A positive anti-HAV IgG result is indicative of protective immunity. 

For diagnosis of acute HAV infection, physicians should order both hepatitis A IgM and hepatitis A IgG antibodies. For confirmation of immunity, HAV IgG antibody is the test of choice.

Results are reported as positive or negative. Reference value is negative.

Specimen requirement is one red top serum gel tube of blood.

HAV nucleic acid amplification testing (PCR) for HAV RNA is also available for detection of virus in blood or feces, but is usually not required for diagnosis. 

References

Lemon SM, et al, Type A viral hepatitis: a summary and update on the molecular virology, epidemiology, pathogenesis and prevention, J Hepatol.2017;SO168-8278

Foster MA et al. Increase in hepatitis A infections-United States, 2013-2018. MMWR Morb Mortal Wkly Rep. 2019;68(18):413-415.

Desai AN and Kim Ay, Management of Hepatitis A in 2020-2021, JAMA, published online July 6, 2020, E1-E2.