Skip to content
Blood Test Tracker

H. pylori Stool Antigen

A stool test that looks for H. pylori proteins and shows an active infection. Recent antibiotics, acid reducers or bismuth can hide a true infection.

AI-verified against cited sources. Awaiting expert reviewAlso called HpSALOINC 17780-8

What it is

H. pylori is a bacterium that can live in the lining of the stomach. It is a common cause of gastritis and ulcers, though many people never have symptoms. This test checks a small stool sample for H. pylori antigens, which are proteins that come from the bacteria. Because these proteins are only in the stool while bacteria are present, a positive result points to a current infection rather than a past one.

Why it matters

Stool antigen and breath tests are the usual ways to find out whether H. pylori is behind symptoms such as upper belly pain, bloating or nausea, and to check whether treatment worked. The monoclonal antibody stool tests are very accurate, with a pooled sensitivity of about 93% and specificity of about 96% in one review. They can miss an infection if you recently used acid reducers, bismuth or antibiotics.

If it’s high

A positive result means H. pylori proteins were found, which points to a current infection. Many people with H. pylori have no symptoms, but treating it can let the stomach lining heal. Your clinician will talk with you about what to do next.

Common causes

  • A current H. pylori infection of the stomach

What can help

  • Talk with your clinician about treatment options
  • Ask when and how to confirm that treatment worked, because tests done too soon can be falsely negative

What can affect your result

  • Recent acid reducers, antibiotics or bismuth: can cause a false negative (Labcorp says within two weeks; some reviews say within a month for antibiotics)
  • Test type: monoclonal antibody tests are more accurate than polyclonal ones
  • Sample handling: keep it refrigerated and deliver it within 72 hours
  • A positive result is reliable even if you were taking these medicines
  • Proton pump inhibitors, antibiotics and bismuth products can suppress the bacteria and cause a false negative. Labcorp says a negative result within two weeks of these may be false and should be repeated on a new sample two weeks after treatment is stopped. Some reviews extend the antibiotic window to a month. Do not stop any medicine unless your clinician tells you to.
  • A positive result is considered accurate even if you were taking these medicines (Labcorp).
  • The sample must be kept refrigerated and reach the lab within 72 hours, or be frozen (Labcorp).
  • Monoclonal antibody tests are more accurate than polyclonal ones, and in children ELISA-based tests performed better than rapid immunochromatography tests in one review.

The test shows whether bacteria are present at the time of the sample. After treatment, testing too soon can miss bacteria that are suppressed but not gone.

When to talk to a clinician

Get medical help right away for signs of stomach bleeding: black or tarry stool, red blood in vomit or vomit that looks like coffee grounds, sudden or severe belly pain that does not go away, dizziness or fainting, or a rapid pulse. Otherwise, talk with your clinician about a positive result soon.

Questions you could ask

  • Do any of my medicines affect how I should time this test?
  • If my result is negative but my symptoms continue, could my medicines have affected it?
  • What treatment options make sense for me?
  • When and how should we check that the infection is gone?

Questions people ask

Can I take my usual stomach medicines before this test?

Acid-reducing medicines, antibiotics and bismuth products can make the test miss an infection. Labcorp says a negative result within two weeks of these may be false and should be repeated on a new sample after they are stopped. Ask your clinician before changing any medicine, and do not stop one on your own.

How is this different from the blood antibody test?

Antibodies in the blood can stay for months after the bacteria are gone. The stool antigen test looks for proteins from the bacteria themselves, so it points to a current infection.

Can I use it to check whether treatment worked?

Yes. A stool antigen or breath test is used to confirm that the infection is gone when endoscopy is not needed. Timing matters, so ask your clinician when to test.

Show the science and sources

For clinicians and researchers

The test detects H. pylori antigen in stool, usually by enzyme immunoassay (Labcorp reports it as 'H. pylori Stool Ag, EIA'). Stool monoclonal antibody tests are superior to polyclonal ones, with a pooled sensitivity of 93% and specificity of 96%, and ELISA-based tests perform better than immunochromatography-based ones, including in children. The stool antigen test and the urea breath test detect active infection, and the monoclonal stool antigen test and the 13C urea breath test are the preferred non-invasive tests of active infection. Any drug that lowers bacterial numbers below the detection limit can cause false negatives, in particular recent proton pump inhibitors, bismuth compounds or antibiotics. Labcorp says a negative result within two weeks of these should be repeated on a new specimen two weeks after stopping, and that a positive result under these conditions is accurate. Where endoscopy is not needed, the stool antigen test or breath test is also used to check that the infection has gone after treatment. The 2024 ACG guideline addresses who should be tested and whether every treated patient needs a test of cure. In a review of 99 studies, stool antigen had a sensitivity of about 83% at a specificity of 90%, a lower figure than the monoclonal-only pooled estimate, which shows that results vary by assay.

LOINC 17780-8 (primary), 31843-6, 80373-4. Specimen: stool.

Sources

  1. Helicobacter pylori Stool Antigen (test 180764), Labcorp
  2. Helicobacter pylori (H. pylori) Tests, MedlinePlus Medical Tests (National Library of Medicine)
  3. What Is New in Helicobacter pylori Diagnosis. An Overview, Journal of Clinical Medicine (2021)
  4. ACG Clinical Guideline: Treatment of Helicobacter pylori Infection, American Journal of Gastroenterology (2024)

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

Related markers