Interpretation of Reactive Hepatitis B Core Antibody IgM
A reactive Hepatitis B core antibody IgM (IgM anti-HBc) test strongly indicates acute hepatitis B virus infection and is the primary serologic marker for diagnosing acute HBV infection. 1, 2
Clinical Significance of IgM Anti-HBc
- 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
- A positive IgM anti-HBc result during acute hepatitis is indicative of acute HBV infection even in HBsAg-negative patients 2
- IgM anti-HBc is the most reliable marker for distinguishing acute from chronic HBV infection 1, 3
- The presence of IgM anti-HBc helps identify otherwise undiagnosed HBV infections in HBsAg-negative patients during the "window period" 2, 4
Complete Serologic Interpretation
The interpretation of IgM anti-HBc must be considered alongside other serologic markers:
- HBsAg positive + IgM anti-HBc positive + Anti-HBs negative: Acute hepatitis B infection 1
- HBsAg negative + IgM anti-HBc positive + Anti-HBs negative or positive: Acute resolving hepatitis B infection (window period) 1
- HBsAg positive + IgM anti-HBc negative + Anti-HBs negative: Chronic hepatitis B infection 1
Important Clinical Considerations
- 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 due to its low positive predictive value in asymptomatic persons 1
- In patients with chronic HBV infection, IgM anti-HBc can persist at low levels during viral replication or during exacerbations of chronic infection 1
- Quantitative measurement of IgM anti-HBc can help differentiate between acute infection (high titers) and chronic infection with reactivation (lower titers) 2, 5
- Persistence of IgM anti-HBc beyond 6 months may indicate progression to chronic hepatitis 6, 5
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
- Patients with chronic HBV infection should be referred for evaluation to a physician experienced in the management of chronic liver disease 1
- Close contacts of patients with acute HBV infection should be screened and offered vaccination if susceptible 1
Pitfalls and Caveats
- False-positive IgM anti-HBc test results can occur, particularly in asymptomatic persons 1
- A negative IgM anti-HBc test in patients with acute HBsAg-positive hepatitis may indicate that another factor (such as delta virus, hepatitis A, or cytomegalovirus) is the cause of liver damage in a previously unrecognized HBsAg carrier 3
- The presence of rheumatoid factor can potentially cause false-positive results in some assays 4
- Different assays may have different cutoff values, affecting interpretation of results 2, 5