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The presence of IgM antibody to hepatitis B core antigen (Anti-HBc-IgM) is a crucial indicator of acute hepatitis B infection. This specific antibody typically appears during the early phase of infection and signifies that the virus is actively replicating within the body. In a patient presenting with symptoms such as abdominal pain, nausea, and jaundice (change in skin color), the detection of this IgM antibody can help confirm a recent infection with the hepatitis B virus.

When evaluating other test options, Anti-HBe represents the presence of antibodies indicating resolution of infection or lower levels of viral replication, rather than an acute phase. Anti-HBs signifies recovery and immunity from hepatitis B, often occurring after the infection has resolved, thereby not indicating acute infection. Lastly, while the presence of IgG antibody to hepatitis B core antigen (Anti-HBc-IgG) suggests past infection, it does not indicate an ongoing acute infection. Therefore, the test that confirms the acute phase of hepatitis B, particularly in the context of the symptoms presented, is indeed the IgM form of the antibody to hepatitis B core antigen.