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Blood Test Tracker

Hepatitis B Core Antibody, IgM

A short-lived antibody that appears early in a new hepatitis B infection. A positive result is linked to infection within roughly the past six months.

AI-verified against cited sources. Awaiting expert reviewAlso called Anti-HBc IgM, IgM anti-HBc, HBc IgMLOINC 24113-3

What it is

IgM anti-HBc is the early form of the antibody to the core of the hepatitis B virus. Your body makes it when an infection is new, and it fades over the following months. It's usually ordered when someone has symptoms of hepatitis or a possible recent exposure, often together with HBsAg and hepatitis A and C tests in an acute hepatitis panel.

Why it matters

It helps tell a new (acute) infection from an old or long-term one. It's also useful in the short window of a new infection when HBsAg has already cleared but the surface antibody (anti-HBs) isn't detectable yet. The CDC advises ordering it only when new hepatitis B is a concern.

If it’s high

A positive result is usually linked to a recent hepatitis B infection, within about the past six months. Less often, it shows up during a flare of long-term hepatitis B, and it can also be a false positive. Your clinician will read it together with your HBsAg and your other results.

Common causes

  • A new (acute) hepatitis B infection
  • A flare or reactivation of long-term (chronic) hepatitis B
  • The window period of a new infection, when HBsAg has cleared but anti-HBs is not detectable yet
  • A false-positive result

What can help

  • Contact your clinician promptly to go over the result with your other hepatitis B tests
  • Ask about supportive care, liver blood tests, and whether to avoid alcohol while your liver recovers
  • Ask about testing and vaccination for the people you live with and for sexual partners

What can affect your result

  • Timing: it appears around when symptoms begin and fades over several months
  • It can be positive during flares of long-term hepatitis B
  • A negative IgM does not rule out hepatitis B when HBsAg is positive, because long-term infection often has a negative IgM
  • Biotin supplements can interfere with some immunoassays
  • Mayo Clinic Laboratories asks patients to avoid biotin (vitamin B7) supplements for 24 hours before its acute hepatitis profile, which includes this test.
  • It can be positive during a flare or reactivation of long-term hepatitis B, not only in a new infection (CDC).

Appears around the time symptoms start and fades over the following months. CDC describes a positive result as infection within about the past six months, and the Hepatitis B Foundation says it declines within roughly 6 to 9 months.

When to talk to a clinician

Contact your clinician promptly about a positive result. Get urgent care for yellow skin or eyes, dark urine, severe belly pain, repeated vomiting or confusion.

Questions you could ask

  • Why was this test ordered for me?
  • What do my other hepatitis B results say about whether this is a new infection?
  • Which follow-up tests do I need, and when should they be repeated?
  • Should the people close to me be tested or vaccinated?

Questions people ask

Does a positive IgM anti-HBc mean I have a new infection?

Usually, but not always. It is most often linked to an infection within about the past six months. It can also be positive during a flare of long-term hepatitis B. Your clinician will read it along with your HBsAg and other results.

Why was this ordered along with HBsAg?

Each test can miss part of the story. HBsAg can already be gone while anti-HBs hasn't appeared yet. IgM anti-HBc can fill that gap, so the two are often ordered together when someone has symptoms of hepatitis.

Show the science and sources

For clinicians and researchers

IgM anti-HBc is generally detectable when symptoms appear (Hepatitis B Foundation) and marks recent infection (CDC: within less than six months). It can also be positive during severe flares or reactivation of chronic hepatitis B, so it is read with HBsAg, total anti-HBc, anti-HBs and the clinical picture. Mayo Clinic Laboratories advises adding IgM anti-HBc when acute infection is being evaluated, because HBsAg and anti-HBs may both be undetectable during the window period. Typical presentation of acute infection is HBsAg positive, total anti-HBc positive, IgM anti-HBc positive and anti-HBs negative (CDC). Mayo Clinic Laboratories runs an electrochemiluminescence immunoassay and reports a negative reference value. The CDC advises ordering it only when acute infection is a concern.

LOINC 24113-3 (primary), 31204-1, 5185-4. Specimen: serum-or-plasma.

Sources

  1. Clinical Testing and Diagnosis for Hepatitis B, CDC
  2. Acute Viral Hepatitis Profile, Serum (test AHEP), Mayo Clinic Laboratories (Extended Catalog)
  3. Hepatitis B Virus Surface Antigen Screen, Serum (test HBGSN), Mayo Clinic Laboratories (Extended Catalog)
  4. Understanding Your Hepatitis B Test Results, Hepatitis B Foundation

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

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