The Hepatitis immunoglobulin M (IgM) anti-HAV test is a serologic test that assesses the presence of the acute-phase IgM antibody. Recall that IgM is the first antibody to be produced upon a new infection. Thus, for all infections, IgM serves as a marker of recent infection. This is in contrast to IgG which is produced later in the course of infection and typically endures much longer. IgM antibodies for a specific antigen will spike early in the course of disease and then wane. Anti-HAV IgM levels usually peak within the first month after exposure/infection and levels will remain detectable for 3-6 months. Anti-HAV IgM will also be present after HAV vaccination. Anti-HAV IgG is also a common test for HAV infection but it is not typically found on the acute hepatitis panel since the presence of IgG is more indicative of a chronic, or resolved infection rather than an acute one.
The anti-HAV IgM assay is initially performed as a qualitatively test, that is, it is simply reported as 'reactive' or 'nonreactive'. Many immunoassay platforms will also have an intermediate or 'gray zone' in which a result is deemed neither reactive nor nonreactive. When an indeterminant result is obtained it is common practice to repeat the assay after checking the specimen and recentrifugation. If the specimen still repeats in the gray zone, then a new specimen should be obtained, or a quantitative confirmation is ordered.
Anti-HAV IgM indicates relatively recent infection with HAV.
