From the Guidelines
Hepatitis A is diagnosed primarily through blood tests that detect anti-HAV antibodies, with the most important test being the IgM anti-HAV antibody, which appears early in the infection and indicates acute hepatitis A. The diagnosis of hepatitis A cannot be made on clinical grounds alone; serologic testing also is required 1. The presence of IgM antibody to HAV is diagnostic of acute HAV infection. A positive test for total anti-HAV indicates immunity to HAV infection but does not differentiate current from previous HAV infection 1.
Key Laboratory Tests
- IgM anti-HAV antibody: appears early in the infection and indicates acute hepatitis A, typically becomes detectable 5-10 days after infection and remains positive for 3-6 months 1
- Total anti-HAV antibody testing: measures both IgM and IgG antibodies, can determine if someone has immunity from past infection or vaccination 1
- Liver function tests: including alanine aminotransferase (ALT) and aspartate aminotransferase (AST), which are typically elevated during acute infection 1
- Bilirubin levels: may be increased if jaundice is present 1
Additional Testing
- HAV RNA detection by PCR: can identify the virus in stool or blood during early infection before antibodies develop, although not routinely used for diagnosis 1 These tests help clinicians distinguish hepatitis A from other forms of viral hepatitis or liver disease, which is important for proper patient management and public health interventions 1.
From the Research
Laboratory Tests for Diagnosing Hepatitis A
The diagnosis of Hepatitis A virus (HAV) infection is typically made based on the presence of anti-HAV immunoglobulin M (IgM) antibodies in patients with clinical features of acute hepatitis 2.
- The anti-HAV IgM test is the primary laboratory test used to diagnose acute HAV infection.
- Some patients may show a negative serology at initial presentation, which can complicate the diagnosis of hepatitis A (HA) 2.
- In such cases, the test should be repeated, particularly in patients with features of the initial phase of hepatitis and a high cutoff index (COI) value of anti-HAV IgM 2.
- An avidity test for anti-HAV IgG can also be used to distinguish acute infection from immune reactivation, with low-avidity antibodies indicating acute infection and high-avidity antibodies indicating past infection or immune reactivation 3, 4.
Interpretation of Serological Test Results
The interpretation of serological test results for HAV infection can be challenging, especially in cases with low-level reactive anti-HAV IgM results 5.
- A study found that all confirmed cases of acute HAV infection had anti-HAV IgM > 4.0, and a diagnosis other than acute HA was identified in 63.6% of low-level reactive anti-HAV IgM results 5.
- The use of an interpretive algorithm, including a clinically significant cut-off value for anti-HAV IgM, can improve the accuracy of reports sent to clinicians 5.
- The avidity test for HAV-IgG antibodies can also help improve the diagnostic yield, particularly in elderly patients 3, 4.
Other Laboratory Tests
While the anti-HAV IgM test is the primary laboratory test used to diagnose acute HAV infection, other tests such as the detection of HAV RNA or antigen can also be used in certain cases 2, 6.
- However, these tests are not always necessary and may not be available in all laboratories.
- The diagnosis of acute HAV infection is typically based on the presence of anti-HAV IgM antibodies, and other tests are used to support the diagnosis or to distinguish acute infection from past infection or immune reactivation.