Interpretation of Reactive Hepatitis B Core Antibody IgM
A reactive Hepatitis B core antibody IgM (IgM anti-HBc) test indicates acute hepatitis B virus infection or an acute exacerbation of chronic hepatitis B infection. 1
Primary Clinical Significance
- IgM anti-HBc appears at the onset of symptoms or liver test abnormalities in acute HBV infection and typically persists for up to 6 months if the infection resolves 1, 2
- IgM anti-HBc is the most reliable marker for distinguishing acute from chronic HBV infection in symptomatic patients 1
- A strong positive reaction for IgM anti-HBc during acute hepatitis is indicative of an acute HBV infection even in HBsAg-negative patients (during the "window period") 3
Complete Serologic Interpretation
The interpretation of a reactive IgM anti-HBc depends on other serologic markers:
- HBsAg positive + IgM anti-HBc positive + Anti-HBs negative = Acute hepatitis B infection 1, 2
- HBsAg negative + IgM anti-HBc positive + Anti-HBs negative or positive = Acute resolving hepatitis B infection (window period) 1, 2
- HBsAg positive + IgM anti-HBc negative + Anti-HBs negative = Chronic hepatitis B infection 1, 2
Quantitative Considerations
- High titers of IgM anti-HBc (cut-off index >2.0) are typically seen in acute hepatitis B infection 4
- Lower titers of IgM anti-HBc (cut-off index <2.0) may be detected in patients with chronic HBV infection, particularly during flares of disease activity 4, 2
- In chronic HBV infection, IgM anti-HBc is predominantly of the 7-8S (low molecular weight) variety, whereas in acute infection it is predominantly 19S (high molecular weight) 5
Clinical Applications
- Testing for IgM anti-HBc should be limited to persons with clinical evidence of acute hepatitis or an epidemiologic link to a person with HBV infection 1, 2
- IgM anti-HBc testing helps identify HBV infection in HBsAg-negative patients during the "window period" when HBsAg has disappeared but anti-HBs has not yet appeared 3, 6
- A negative IgM anti-HBc test in an HBsAg-positive patient with acute hepatitis suggests that the patient is a chronic carrier with liver damage due to another cause (such as hepatitis delta virus, hepatitis A, or other viral infections) 7
Prognostic Value
- Patients with acute hepatitis B who are positive for IgM anti-HBc have a much lower risk of developing chronic infection (4%) compared to those who are negative for IgM anti-HBc (84%) 7
- The presence of IgM anti-HBc in chronic HBV carriers correlates with the degree of inflammatory activity in the liver 4
Management Implications
- No specific treatment exists for acute hepatitis B; supportive care is the mainstay of therapy 1
- Patients with confirmed acute HBV infection should be monitored for resolution of the infection or progression to chronic infection 1
- If chronic HBV infection is diagnosed, referral to a specialist experienced in managing chronic liver disease is recommended 1, 8
- Close contacts of patients with acute HBV infection should be screened and offered vaccination if susceptible 1
Important Caveats
- False-positive IgM anti-HBc test results can occur, particularly in asymptomatic persons 1, 2
- In patients with chronic HBV infection, IgM anti-HBc can persist at low levels during viral replication or during exacerbations of chronic infection 1, 2
- The positive predictive value of IgM anti-HBc testing is low in asymptomatic persons 2