Is the H. pylori stool test or the blood test more accurate?

For finding a current infection, the stool antigen test is the better choice. Before treatment, the monoclonal stool antigen test was positive in about 94% of infected people and negative in about 97% of uninfected people. The blood IgG antibody test cannot separate a current infection from a past one. For that reason, Maastricht VI and ACG 2024 both favor stool, breath or biopsy tests for decisions about active infection.

How long do I need to stop omeprazole or other PPIs before an H. pylori stool test?

Guidelines expect PPIs such as omeprazole to be held for about 2 weeks before a stool antigen or breath test. Antibiotics and bismuth are held for about 4 weeks. Arrange any pause with the prescriber; do not stop on your own. During the gap, get prompt care for black stools, vomiting blood or trouble swallowing.

When should I retest after H. pylori treatment to confirm it is gone?

The ACG 2024 guideline recommends a test of cure for every treated patient, at least 4 weeks after the last treatment dose. The test is a breath, stool or biopsy test, with PPIs held for about 2 weeks beforehand. Your clinician arranges the timing.

Why is my H. pylori blood test still positive after treatment?

The H. pylori IgG antibody is immune memory. It can stay positive for months to years after the bacteria are cleared. A positive blood antibody test after treatment does not show that treatment failed. Only a breath, stool or biopsy test can answer that.

Helicobacter pylori Antigen (Stool): what it measures and how to read it

The distinctions

01
Current infection versus past exposure
The stool antigen test finds pieces of H. pylori living in the stomach now. The blood IgG antibody test finds the immune system's memory of H. pylori, which can last for years after a cure. A positive blood test can therefore reflect an infection that is already gone. Only a stool, breath or biopsy test can show whether the infection is still there or confirm a cure.

The H. pylori stool antigen test looks for pieces of Helicobacter pylori in a small stool sample. H. pylori is a bacterium that lives in the stomach lining. An antigen is a fragment of the bacterium's own protein, so finding one means the bacteria are there now. A positive result points to a current infection. A negative result can be trusted only if you took no proton pump inhibitor (PPI, an acid-reducing pill such as omeprazole) in the 2 weeks before the sample. You also need to have taken no antibiotics and no bismuth (the active ingredient in Pepto-Bismol) in the 4 weeks before ¹².

Key points

01The stool antigen test and the blood antibody test answer different questions. The stool test asks whether H. pylori is there now. The blood IgG antibody test asks whether it was ever there.
02The blood antibody can stay positive for months to years after a successful cure. A positive blood test on its own can therefore reflect an old infection ².
03Before treatment, the monoclonal stool antigen test was positive in about 94% of infected people (its sensitivity) and negative in about 97% of uninfected people (its specificity) ³. Monoclonal means the lab test is built on antibodies that each target one H. pylori protein.
04The 2024 American College of Gastroenterology (ACG) guideline calls for a test of cure for every treated patient, at least 4 weeks after treatment ends ¹.
05Black or bloody stools, vomiting blood or trouble swallowing need prompt care, whatever the stool result says. The full list is in the alarm box further down.

What a positive or negative stool antigen result means

The H. pylori stool antigen result comes back as positive, negative or, now and then, indeterminate. There is no number to place on a scale. With a yes-or-no result, the conditions of the test matter most; our guide on how to read any lab result covers this in general. For the stool antigen test, the condition that matters most is which medicines you took beforehand. Guidelines recommend the monoclonal version of the test ², and the figures below come from it.

Result	What it means	Usual next step
Positive	H. pylori antigen was found, so an active infection is likely. False positives are uncommon: about 97 in 100 uninfected people test negative ³.	The clinician usually prescribes an acid-reducing pill plus antibiotics, often for 14 days and sometimes with bismuth. A test of cure follows at least 4 weeks after the last dose ¹.
Negative, with no PPI in 2 weeks and no antibiotics or bismuth in 4 weeks	An active infection is unlikely but not ruled out. The test finds about 94 in 100 active infections, so about 6 in 100 are missed ³.	If symptoms continue, H. pylori is a much less likely cause. The clinician decides whether to look for other causes or to retest. Alarm symptoms still need prompt care.
Negative, but a PPI, antibiotic or bismuth was taken inside the washout window	The negative may be false. These medicines suppress the bacteria below the level the test can detect ¹².	Ask the ordering clinician whether to repeat the test after a washout arranged with your prescriber.
Negative, tested less than 4 weeks after treatment ended	This negative does not count as a test of cure. Suppressed bacteria can grow back after the sample ¹.	Guidelines call for a repeat test at least 4 weeks after the last treatment dose. The ordering clinician arranges it ¹.
Indeterminate	The lab could not call the result either way.	The test is usually repeated on a fresh sample.

Stool test or blood test: which shows a current infection

Stool antigen shows a current infection; the blood antibody shows past exposure

Stool antigen test✓ Use for diagnosis and test of cure

Monoclonal stool antigen

What it detectsPieces of live H. pylori in stool today

Positive after a cure?No, it turns negative once the bacteria are gone

Usable as a test of cureYes, at least 4 weeks after treatment ends

Affected by PPIs, antibiotics, bismuthYes, they can cause a false negative

Typical accuracyPositive in about 94 in 100 infected people; negative in about 97 in 100 uninfected people, before treatment

Blood antibody test (IgG)Not for checking a cure

Serology

What it detectsAntibodies your immune system made at some point

Positive after a cure?Often yes, for months to years

Usable as a test of cureNo

Affected by PPIs, antibiotics, bismuthNo, because it does not measure the bacteria

Typical accuracyCannot tell a current infection from a past one

Sources: Maastricht VI/Florence consensus, Gut 2022 ²; Chey et al., ACG Clinical Guideline, Am J Gastroenterol 2024 ¹; Gisbert et al., Am J Gastroenterol 2006, for stool antigen accuracy ³.

The blood test measures IgG, a type of antibody the immune system makes after it meets H. pylori. IgG works like a memory of that meeting. The memory fades slowly, so the blood test can stay positive long after the bacteria are gone ². A positive H. pylori antibody test therefore cannot tell a current infection from one cured years ago. Maastricht VI and ACG 2024 both name three kinds of test for active infection: the urea breath test, the stool antigen test and biopsy-based tests. Both rule out serology (the blood antibody test) for confirming a cure ¹².

	Stool antigen	Urea breath test	Blood IgG antibody	Biopsy (during endoscopy)
What it measures	H. pylori protein in stool	Gas that live H. pylori make when they break down a swallowed test dose of urea	Antibodies from any past exposure	The bacteria in a tissue sample from the stomach
Shows a current infection?	Yes	Yes	No	Yes
Usable as a test of cure?	Yes	Yes	No	Yes
Thrown off by recent PPIs, antibiotics, bismuth?	Yes	Yes	No	Yes
Preparation	No fasting; collect a small sample	Usually a short fast; the lab sets the window	None	Fasting and sedation for the endoscopy
When it is the usual choice	Diagnosis or test of cure without endoscopy	Diagnosis or test of cure without endoscopy	Rarely the right choice for a treatment decision	When endoscopy is already planned, for example for dyspepsia at age 60 or over ⁵

Fecal calprotectin is a different stool test. It measures inflammation in the bowel wall and says nothing about H. pylori. The two stool tests are usually ordered for different symptoms, so do not read one against the other.

Medicines that can hide H. pylori

PPIs, antibiotics and bismuth all suppress H. pylori. With fewer bacteria in the stomach, less antigen reaches the stool, and the test can read negative while the infection is still there. That is why Maastricht VI and ACG 2024 set washout windows before a stool antigen or breath test ¹².

Medicine type	Common examples	Usual washout before testing	Effect on the test
Proton pump inhibitors (PPIs)	Omeprazole (Prilosec), esomeprazole (Nexium), pantoprazole, lansoprazole	About 2 weeks ¹²	Suppress the bacteria; can cause a false negative
Antibiotics	Any course, including amoxicillin, clarithromycin or metronidazole taken for another illness	About 4 weeks ¹²	Can reduce the bacteria below detection
Bismuth	Bismuth subsalicylate (Pepto-Bismol)	About 4 weeks ¹²	Acts directly against H. pylori; can cause a false negative ²
H2 blockers and antacids	Famotidine (Pepcid), calcium carbonate antacids	No standard window; check with the lab	They suppress acid less than PPIs, so they are less likely to cause a false negative

Active bleeding from an ulcer also makes the stool antigen test and the other tests less sensitive. Maastricht VI advises that a negative test taken during upper gut bleeding be confirmed with a later test ².

Why H. pylori is worth finding

4.4 billionPeople estimated to carry H. pylori worldwide in 2015Prevalence is lower in North America than in much of Africa, Latin America and Asia ⁴

H. pylori is common ⁴ and often causes no symptoms. It is still a leading cause of peptic ulcers, which are sores in the lining of the stomach or the first part of the small intestine ². The International Agency for Research on Cancer classes H. pylori as a Group 1 carcinogen, its category for definite causes of cancer, because long-term infection raises the risk of stomach cancer ². H. pylori can also contribute to iron deficiency and low vitamin B12. For that reason, an unexplained low ferritin or hemoglobin can lead a clinician to test for it ².

Who should be tested

Maastricht VI and the ACG and Canadian Association of Gastroenterology (CAG) dyspepsia guideline recommend testing for active H. pylori infection in these situations ²⁵:

A current or past peptic ulcer ².
Dyspepsia (recurring upper-belly pain, burning or fullness after eating) in people under 60, where the ACG/CAG guideline favors a test-and-treat approach ⁵.
Iron deficiency anemia with no other explanation ².
Vitamin B12 deficiency with no other explanation ².
People on long-term aspirin or NSAIDs (anti-inflammatory painkillers such as ibuprofen) who have had ulcers before ².
Immune thrombocytopenia (ITP, an immune condition that lowers platelets; see the blood count hub for the basics) and gastric MALT lymphoma, a rare lymphoma of the stomach lining ².
First-degree relatives (parents, siblings, children) of people with stomach cancer ².

How to confirm the treatment worked

H. pylori treatment does not clear the infection in every patient, and most people feel the same whether it worked or not. For that reason, the ACG 2024 guideline recommends a test of cure for every treated patient ¹.

1Treatment endsStart counting from the last dose of the prescribed H. pylori treatment.
2Wait at least 4 weeksA test taken sooner can miss bacteria that are suppressed but still alive, so an early negative can falsely reassure you ¹.
3Hold PPIs beforehand, as arranged with the prescriberThe ACG 2024 guideline expects PPIs to be held for about 2 weeks before the test of cure ¹.
4Take a breath, stool or biopsy testThe test of cure is a urea breath test, a stool antigen test or a biopsy-based test. It is never the blood antibody test, which can stay positive after a cure ¹².
5Read the result with the clinicianA negative test of cure taken outside the washout windows means the infection has very likely been cleared. A positive one means the first treatment did not clear it, and the clinician chooses the next step.

How the test works in practice

The stool antigen test needs no fasting. You collect a small sample with a kit from the lab, at home or on site, and return it within the time the kit states.
The stool antigen test is ordered on its own. Routine blood panels do not include it, so the clinician has to request it by name.
Coverage for H. pylori testing depends on the plan and the reason for the test, so check with your insurer or the lab. Self-pay prices vary by lab.
One stool antigen test answers the diagnostic question, and one test of cure after treatment answers whether it worked. More testing usually happens only if symptoms return or an earlier sample fell inside a washout window.
Testing people with no symptoms and no risk factor is not routine in the US. Maastricht VI names close relatives of people with stomach cancer as a group to test. It also supports screening in regions where stomach cancer is common ².

Link · American Journal of Gastroenterology, 2024ACG Clinical Guideline: Treatment of Helicobacter pylori infectionThe current US guideline on treatment and test of cure, including washout timing before testing.doi.org

For related subjects, see the gut hub, the infections hub and the cancer screening hub. If the H. pylori result came with low iron or B12, see the iron and vitamin B12 pages. A clinician works out the cause of a deficiency before any supplement is started. If treatment is about to start, the probiotics page covers the evidence on taking them alongside antibiotics. Check with the prescriber before adding anything to a treatment course.

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Citations

Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.