What Is Hepatitis a IgM?

Natalie M. Smith

Hepatitis A IgM is an antibody produced by the body after a person has recently contracted hepatitis A, a common and acute form of the many hepatitis liver diseases. Doctors diagnose hepatitis A using a panel of tests, one of which can detect hepatitis A IgM, which is present in the blood up to a year after infection. Some patients who test positive for hepatitis A IgM also test positive for hepatitis A IgG. This second antibody can indicate that a patient had hepatitis A in the past, has developed immunity to the disease post-infection, or has been vaccinated against it.


Diagnosis of hepatitis A requires a hepatitis virus panel, which is a series of tests that detects antigens and antibodies indicative of the disease. One of these antibodies is the hepatitis A antibody immunoglobulin M, or hepatitis IgM. Antibodies are proteins produced by the body to fight off infection; thus, the production of hepatitis antibodies is the body's way of fighting off hepatitis. Testing positive for hepatitis A IgM indicates that a patient actively has the disease or has recently been infected, as it is produced only after the first week or so of infection and disappears within one year. Patients who test negative for hepatitis A IgM might still have had hepatitis A in the past, as indicated by other panel tests.

Results of a hepatitis A virus panel might also reveal the presence of both hepatitis A IgM and hepatitis A IgG, or IgG alone. Hepatitis A IgG is another hepatitis-fighting antibody that is produced eight to 12 weeks after infection, but, unlike hepatitis A IgM, it remains in the blood for life. When a hepatitis A test detects both IgM and IgG, this indicates that the patient contracted the disease less recently. The presence of hepatitis A IgG alone indicates that the patient has had hepatitis in the past, but has also developed lifelong immunity and can no longer spread or contract the disease. Patients who are vaccinated against hepatitis also have hepatitis IgG present in their blood.

Of the different types of hepatitis virus, hepatitis A is one of the most common and mildest forms of this liver disease. It is a contagious condition that is usually contracted by ingesting the fecal matter of infected persons, often through contaminated food or drinks. Although some infected patients become severely ill, hepatitis A patients often get well without treatment, and the disease is not long-term. The hepatitis A vaccine, introduced in 1995, is the best form of prevention.

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