The Hepatitis B Core IgM (Anti-HBc IgM) test is a blood test that detects IgM antibodies against the core antigen of the Hepatitis B virus (HBV). 

• IgM antibodies appear early during acute infection and indicate a recent or current Hepatitis B infection.
• Unlike IgG, which persists long-term, IgM is transient, usually present during the first 6 months of infection.