Significance of anti-HBc IgM in the differential diagnosis of viral hepatitis.

IgM antibody to hepatitis B core antigen (anti-HBc IgM) as determined by IgM capture immunoassay is generally present in high titer during acute hepatitis B infection. A strong positive reaction for anti-HBc IgM during acute hepatitis is indicative of an acute HBV infection even in hepatitis B surface antigens (HBsAg)-negative patients. With the help of anti-HBc IgM otherwise unidentified HBV infection can be diagnosed in HBsAg-negative patients and an optimal combination of diagnostic tests for acute hepatitis B infection would therefore include assays for both HBsAg and anti-HBc IgM. In the HBsAg carrier with or without chronic liver disease the presence and meaning of anti-HBc IgM is still a matter for discussion. Detection of a weak positive result for anti-HBc IgM in HBsAg-positive patients without a recent history of acute hepatitis cannot always be regarded as a definite marker of recent hepatitis B infection. However, quantitation of the anti-HBc IgM results seems to improve the clinical value of the test. Comparison of the available anti-HBc IgM assays is needed and may well establish a reliable cut-off level that would differentiate acute from chronic hepatitis B and ongoing from resolving hepatitis B in HBsAg-positive patients.