Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1368 page)

   The total assay detects the presence of anti-HAV total (both IgG and IgM combined). A positive result indicates that the patient had hepatitis A either recently or in the past. IgM antibodies against HAV are detected soon after the onset of symptoms. Persistence of the IgM response is extremely variable, with specific IgM detected for <1 month in some cases to >1 year in others. In most cases, IgM antibodies against HAV persist for a period of 3–6 months, after which they decline to levels that are below detection.

HEPATITIS B CORE ANTIBODY (HBcAb; TOTAL AND IgM)

   Definition

   Hepatitis B core antibodies appear shortly after the onset of symptoms of hepatitis B infection and soon after the appearance of HBsAg and persists for life. Initially, anti-HBcAb consists almost entirely of the IgM class, followed by appearance of anti-HBc IgG, for which there is no commercial diagnostic assay. The anti-HBc total antibodies test, which detects both IgM and IgG antibodies and is the test for anti-HBc IgM antibodies, may be the only markers of a recent hepatitis B infection detectable in the “window period.” The window period begins with the clearance of HBsAg and ends with the appearance of antibodies to HBsAg.

   
Normal range:
Negative.

   Use

   Differential diagnosis of hepatitis; diagnosis of recent or past resolved hepatitis B infection.

Determination of occult hepatitis B infection in otherwise healthy HBV carriers with negative test results for HBsAg, anti-HBs Ab, anti-HBc IgM Ab, HBeAg, and antibodies to HBeAg.

   Interpretation

Increased In

   HBcAb total assay: Acute, chronic, or past resolved hepatitis B infection

   HBcAb IgM assay: Recent infection with hepatitis B virus (≤6 months)

Decreased In

   Normal finding.

   Limitations

   Not produced after hepatitis B immunization.