The following is a marker of acute hepatitis B infection-

HBV-DNA can be measured by PCR in the blood. Viral loads are usually in excess of 105 copies/mL in the presence of active viral replication, as indicated by the presence of e antigen. In contrast, in individuals with low viral replication, who are HBsAg- and anti-HBe-positive, viral loads are less than 105 copies/mL. The exception is in patients who have a mutation in the pre-core protein, which means they cannot secrete e antigen into serum . Such individuals will be anti-HBe-positive but have a high viral load and often evidence of chronic hepatitis. These mutations are common in the Far East, and those patients affected are classified as having e antigen-negative chronic hepatitis. They respond differently to antiviral drugs from those with classical e antigen-positive chronic hepatitis. Measurement of viral load is impoant in monitoring antiviral therapy and identifying patients with pre-core mutants. Specific HBV genotypes (A-H) can also be identified using PCR. In some settings, these may be useful in guiding therapy, as genotype A tends to respond better to pegylated interferon-alfa compared to genotypes C and D. Ref Davidson edition23rd pg 875