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Blood Test Tracker

Hepatitis A antibody, IgM

An early antibody to the hepatitis A virus. A positive result can mean a current or recent hepatitis A infection.

AI-verified against cited sources. Awaiting expert reviewAlso called HAV IgM, anti-HAV IgM, IgM anti-HAVLOINC 13950-1

What it is

Hepatitis A is a viral infection of the liver. It spreads through contaminated food or water, or through close contact with an infected person. IgM is the first antibody the body makes against a new infection. This test looks for IgM against the hepatitis A virus (anti-HAV IgM). Labs report the result as negative (non-reactive) or positive (reactive). IgM usually becomes measurable within about 5 to 10 days of symptoms starting and fades within 6 months.

Why it matters

Symptoms of hepatitis A look like other kinds of viral hepatitis, so a blood test is needed to tell them apart. IgM is the standard antibody test for a current or recent infection. Most people recover fully and become immune for life, according to the WHO. In young children most infections cause no symptoms. The CDC advises doing this test only in people who have symptoms and a suspected infection, because tests done without a reason are more likely to give a false positive.

If it’s high

A positive IgM suggests a current or recent hepatitis A infection, especially if you have symptoms such as tiredness, nausea, dark urine or yellow skin or eyes. It can also be a false positive, and it can appear in the weeks after the hepatitis A vaccine. Your clinician reads it with your symptoms, exposures and liver tests.

Common causes

  • A current or recent hepatitis A infection
  • A recent hepatitis A vaccine dose, when IgM can still be found
  • A false-positive result, which is more likely when the test is done without symptoms or a known exposure

What can help

  • Ask your clinician about liver blood tests (ALT, AST and bilirubin) to see how your liver is doing
  • Ask about rest, fluids and what to avoid while your liver recovers
  • Ask which close contacts should speak with their own clinician about protection after exposure, since the CDC says protection given to contacts within 2 weeks of exposure is highly effective

What can affect your result

  • Timing: IgM may not be measurable in the first days of symptoms
  • Recent hepatitis A vaccination can cause a positive result
  • Testing without symptoms or a known exposure raises the chance of a false positive
  • IgM has occasionally been reported more than a year after an infection
  • Recent hepatitis A vaccination can cause a positive IgM. IgM has been found 2 to 3 weeks after one dose in 8% to 20% of adults.
  • False positives happen, mostly when people with no symptoms and no known exposure are tested. The CDC advises testing only people with symptoms and suspected hepatitis A.
  • High-dose biotin supplements can affect some immunoassays. Mayo asks people to avoid biotin for 24 hours before the draw.

IgM usually becomes measurable within about 5 to 10 days of symptoms starting, peaks within a month and fades to undetectable within 6 months (ACIP).

When to talk to a clinician

A positive IgM is something to discuss with your clinician soon, especially if you feel ill. Contact a clinician promptly if you have yellow skin or eyes, dark urine, pale stools, belly pain, or nausea that keeps you from drinking fluids. Call 911 or your local emergency number for confusion, trouble staying awake, or bleeding that does not stop.

Questions you could ask

  • Why was this test ordered, and how will the result change what we do?
  • Should we repeat the test if my symptoms started only a few days ago?
  • Could this be a false positive, for example from a recent vaccine?
  • Do we need liver blood tests or a test for the virus itself?
  • Which people around me should talk to their own clinician about protection?

Questions people ask

Does a positive hepatitis A IgM mean I have hepatitis A?

It suggests a recent infection, especially with symptoms, but it is not proof. False positives happen, and a recent vaccine can cause a positive result. Your clinician will look at your symptoms, exposures and liver tests.

Can the hepatitis A vaccine make this test positive?

Yes. The vaccine can produce IgM that tests pick up in the first weeks after a dose. In one set of data, IgM was found 2 to 3 weeks after a single dose in 8% to 20% of adults.

How long does hepatitis A IgM last?

It usually peaks within a month and fades to undetectable within 6 months of infection. In rare cases a positive result has been reported more than a year later.

Show the science and sources

For clinicians and researchers

Anti-HAV IgM is measured by qualitative immunoassay: Mayo uses electrochemiluminescence (ECLIA), ARUP chemiluminescent immunoassay (CLIA), and Quest an immunoassay, with reference results of negative (Mayo, ARUP) or non-reactive (Quest). Per the ACIP (2020), diagnosis requires IgM anti-HAV in serum or HAV RNA in serum or stool. IgM becomes detectable within 5 to 10 days of symptom onset in most persons, usually peaks within 1 month and falls to undetectable within 6 months after infection. Positive IgM more than 1 year after infection has been reported, as have likely false positives in persons without evidence of recent HAV infection, so testing is advised only for symptomatic persons with suspected hepatitis A. HepA vaccination can induce detectable IgM anti-HAV, particularly within a few weeks (8% to 20% of adults 2 to 3 weeks after one dose). The CDC serologic-course text gives a slightly different window, with IgM present from about 5 to 10 days before symptoms to 6 months after infection. The WHO notes that RT-PCR for HAV RNA can detect infection early, before IgM appears. When IgM is positive and total anti-HAV is positive, the CDC lists current infection, recent infection or recent vaccination as possibilities, and IgM alone can be a current infection or a false positive or cross-reaction.

LOINC 13950-1 (primary), 22314-9, 22315-6, 5181-3. Specimen: serum.

Sources

  1. Clinical Screening and Diagnosis for Hepatitis A, US Centers for Disease Control and Prevention
  2. Prevention of Hepatitis A Virus Infection in the United States: Recommendations of the Advisory Committee on Immunization Practices, 2020, MMWR Recommendations and Reports (2020)
  3. Hepatitis A, World Health Organization
  4. Hepatitis A Virus IgM Antibody, Serum (test HAIGM), Mayo Clinic Laboratories (via testcatalog.org)
  5. Hepatitis A Virus Antibody, IgM (test 0020093), ARUP Laboratories
  6. Hepatitis A IgM Antibody (test code 512), Quest Diagnostics

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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