H. Pylori IgG Test: What Do Your Results Mean?

An H. pylori IgG test measures antibodies your immune system produced in response to Helicobacter pylori, a bacterium that can live in the stomach lining. A positive result means your body has mounted an immune response to H. pylori at some point, but it does not by itself tell you whether the infection is still active right now. That distinction matters more than most people realize, and it shapes nearly every decision that follows the test.

What a Positive Result Actually Tells You

IgG antibodies are part of your immune system’s long-term memory. Once your body encounters H. pylori, it starts producing IgG antibodies, and those antibodies can remain detectable in your blood for months or even years after the bacteria are gone. So a positive IgG result confirms exposure to H. pylori but leaves open the question of timing. You might have an active, ongoing infection. Or you might have been successfully treated years ago and still carry residual antibodies.

This is the single most important thing to understand about IgG serology: it cannot distinguish past from present infection. If you have never been tested or treated for H. pylori before, a positive IgG result is a reasonable indicator that you are likely infected, especially when combined with symptoms like chronic stomach pain, bloating, or nausea. But if you completed a course of treatment in the past, a positive result does not mean the treatment failed. In a large Japanese study, about 41% of people tested positive for IgG antibodies less than a year after successful eradication therapy, and roughly 11% still tested positive six or more years later.¹ Doctors know this and will often recommend a different type of test to check whether the bacteria are actually still present.

What a Negative Result Means, and When It Can Mislead

A negative IgG result is generally reassuring. If you have never been treated for H. pylori, a negative test makes active infection unlikely. The IgG test has strong sensitivity, meaning it rarely misses people who are truly infected. One study comparing serology to a urea breath test found the IgG test’s sensitivity was about 97%, with a negative predictive value around 98%.² In practical terms, if the test says negative, it is very likely correct.

There are exceptions, though. People with significant stomach lining damage, a condition called gastric mucosal atrophy, sometimes produce lower antibody levels that slip below the test’s positive cutoff. Research has found that negative serology results crop up more frequently in people who have moderate to severe atrophy of the stomach lining, even when H. pylori is still present on endoscopy.³ Another study confirmed that among people whose endoscopy showed signs consistent with H. pylori, antibody titers were still higher than in truly uninfected individuals, but not always high enough to cross the threshold for a “positive” lab report.⁴ In these cases, the immune response has weakened alongside the stomach lining itself, so the blood test underestimates what is happening in the stomach.

Young children represent another group where IgG testing is less reliable. A meta-analysis of antibody-based tests in children found that sensitivity was lower than in adults, partly because younger immune systems may not mount as strong an antibody response to the infection.⁵ For children, doctors generally prefer stool antigen tests or breath tests over serology.

The “Equivocal” or Borderline Zone

Many labs report IgG results in three categories: positive, negative, and equivocal (sometimes called “borderline” or “indeterminate”). The cutoff values vary by manufacturer, but a common scheme uses something like below 10 U/mL as negative, above 15 U/mL as positive, and 10 to 15 U/mL as equivocal. An equivocal result is genuinely ambiguous. It could reflect an early infection where antibodies are still ramping up, a past infection where antibodies are declining, or just normal biological variation around the cutoff.

If your result falls in this range, your doctor will typically recommend a follow-up test using a different method. Repeating the same IgG test a few weeks later rarely helps because antibody levels change slowly. A breath test or stool antigen test, both of which detect active infection rather than immune memory, is the standard next step.

How Antibody Levels Behave After Successful Treatment

One of the biggest sources of confusion is getting a positive IgG test after treatment. Antibody titers do fall after eradication, but not overnight. In the first year after treatment, the median antibody level drops by roughly three-quarters compared to untreated individuals.¹ Over the next several years, levels continue to decline. A separate study tracking patients for over four years after successful eradication found that IgG titers dropped sharply in the first six to nine months and then plateaued, remaining stable at that lower level for years afterward.⁶

The practical implication is straightforward: IgG serology is not the right tool for confirming that treatment worked. Even though titers decline substantially, they can linger above the positive cutoff for a year or more. To verify eradication, guidelines recommend a urea breath test or stool antigen test performed at least four weeks after completing antibiotics.⁷

False Positives and Cross-Reactivity

Another wrinkle with IgG testing is the potential for false positives caused by antibodies to other bacteria. H. pylori shares surface proteins with several other bacterial species. Laboratory research has shown that sera from patients chronically infected with Pseudomonas aeruginosa, Haemophilus influenzae, or Campylobacter jejuni can cross-react with H. pylori antigens, producing antibody titers that look like H. pylori infection when it is not there.⁸ This was identified as a particular concern in patients with cystic fibrosis, who often have chronic Pseudomonas lung infections.

In most everyday clinical situations, this cross-reactivity is not a major problem. A separate study testing for cross-reactivity between H. pylori and C. jejuni found that when properly designed assays were used, the cross-reaction did not meaningfully influence the diagnosis.⁹ Modern commercial assays have been refined to reduce false positives, but the possibility is worth noting if you have a chronic bacterial infection elsewhere in your body and an unexpectedly positive H. pylori result.

How Age Affects Accuracy

IgG testing performs differently depending on the patient’s age. In younger and middle-aged adults, both sensitivity and specificity are excellent. One study found sensitivity of 99 to 100% across all age groups, but specificity dropped from 99% in adults aged 15 to 49 down to 75% in those 65 and older.¹⁰ That means the test rarely misses a true infection at any age, but in older adults it more frequently flags people as positive who are not currently infected. Much of this decline in specificity was attributable to atrophic gastritis, which is more common in older people. When those false positives were removed from analysis, specificity improved to over 93% even in the oldest groups.¹⁰

For older adults, this means a positive IgG test deserves a bit more skepticism. It could be a remnant of past infection, cross-reactivity, or a by-product of stomach lining changes that accumulated over decades. Doctors often follow up with a breath test or stool antigen test to settle the question.

Why H. Pylori Infection Matters

Understanding what your IgG result means matters because H. pylori is not a harmless passenger. The bacterium triggers chronic inflammation in the stomach lining that can progress to gastritis, peptic ulcers, and in some cases gastric cancer.¹¹ The International Agency for Research on Cancer classifies H. pylori as a class I carcinogen, meaning there is sufficient evidence it causes cancer in humans.¹² H. pylori is also linked to a type of stomach lymphoma called MALT lymphoma, which in its early stages often regresses after the infection is eradicated.¹³

Most infected people never develop cancer or lymphoma. Many carry the bacterium for years with no symptoms at all. But for those with symptoms like persistent indigestion, unexplained weight loss, or a family history of stomach cancer, testing and treating the infection is genuinely important. The IgG test often serves as the initial screen that sets this process in motion.

Tests That Detect Active Infection

Because IgG serology has the limitations described above, doctors rely on several other tests that specifically detect current, live infection. These are worth understanding, since a follow-up test is commonly ordered after a positive or equivocal IgG result.

Urea breath test: You swallow a small amount of labeled urea. If H. pylori is present in the stomach, its urease enzyme breaks down the urea and releases labeled carbon dioxide, which is measured in your breath. Meta-analyses report pooled sensitivity around 96% and specificity around 93%.¹⁴ This test tells you whether the bacterium is alive in your stomach right now and is recommended for confirming eradication after treatment.
Stool antigen test: A lab detects H. pylori proteins in a stool sample. Tests that use monoclonal antibodies with an ELISA method are the most reliable, with sensitivity and specificity in the mid-90s.¹⁵ This is a practical option when breath testing is not available, and it is equally valid for confirming eradication.⁷
Rapid urease test: Performed during an endoscopy, this test presses a biopsy of stomach tissue into a gel containing urea. If H. pylori’s urease enzyme is present, the gel changes color. It is cheap and fast, with specificity around 90%, but sensitivity can drop if you are taking acid-suppressing medications or antibiotics.¹⁶

Both the breath test and the stool antigen test can be affected by recent use of proton pump inhibitors (PPIs, the acid-suppressing drugs like omeprazole), antibiotics, or bismuth-containing medications. These can temporarily suppress H. pylori without fully clearing it, leading to false-negative results. One study found the stool antigen test maintained reasonable accuracy even during PPI use, but the safest approach is to stop PPIs at least two weeks before testing and antibiotics at least four weeks before.¹⁷ This is one area where the IgG test actually has an advantage: because it measures your immune response rather than the bacteria themselves, antibody levels are unaffected by medications you are currently taking.

When IgG Testing Is the Right Choice

Given its inability to distinguish past from present infection, you might wonder why the IgG test is used at all. It fills specific roles well. Serology is useful for large-scale screening and epidemiological studies, where the goal is estimating how common H. pylori exposure is in a population rather than making individual treatment decisions. It also works well as a first-line screen in primary care for patients with persistent stomach symptoms who have never been tested or treated before, particularly in regions where H. pylori is common. In those situations, a positive IgG result in a symptomatic, treatment-naive patient usually leads directly to treatment without additional testing.

IgG serology also sidesteps the medication timing issues that plague breath and stool tests. If you just finished a course of antibiotics for something unrelated, or you are in the middle of PPI therapy and your doctor wants a preliminary read on whether H. pylori might be involved in your symptoms, the IgG test can provide useful information without waiting for a medication washout period. The result still needs to be interpreted carefully, but it will not be distorted by whatever you are currently taking.

Rapid Whole-Blood and At-Home Tests

You can find rapid H. pylori antibody tests sold online or in pharmacies, often marketed as fingerstick blood tests with results in minutes. These work on the same IgG principle as the standard lab serology but use a simplified format. Their convenience comes with a trade-off in accuracy. In one study of 300 patients, a rapid whole-blood test achieved a sensitivity of 85% and specificity of 78%, compared with 95% sensitivity and 70% specificity for a standard laboratory serum test.¹⁸ A German primary care study found a similar overall accuracy of about 77% for a rapid test, with a negative predictive value of only 57%, meaning that a negative result from the rapid test was wrong nearly half the time.¹⁹

These numbers are substantially worse than what you get from a lab-processed IgG blood draw. A rapid at-home test that comes back positive is at least a signal worth following up on, but a negative result from one of these kits is not very reliable. If you are using a rapid test because you want a quick answer before deciding whether to see a doctor, treat a positive as a reason to go in and a negative as inconclusive rather than comforting. The standard lab-based serology, and especially a breath or stool test, should follow if your symptoms persist.

Understanding the Numbers on Your Lab Report

Lab reports typically display your IgG level as a numerical value in units per milliliter (U/mL), along with reference ranges and a qualitative interpretation. The exact cutoffs vary by assay manufacturer, so comparing numbers between labs is unreliable. What matters is whether your result falls in the positive, negative, or equivocal range as defined by that particular lab’s kit.

If you have serial results from the same lab using the same assay, trending the numbers over time can be informative. A steadily falling titer after treatment is a good sign, even if the value has not yet dropped below the positive cutoff. As noted earlier, the steepest decline happens in the first several months, and some people plateau at a low-positive level that may persist for years. Conversely, a rising titer in someone who was previously treated could suggest reinfection, though this would need confirmation with a breath or stool test.

One subtle point: a titer that sits just above the cutoff is not necessarily “less infected” than a very high titer. Antibody levels reflect the immune response’s intensity, not the bacterial load in any straightforward way. People with extensive stomach atrophy may paradoxically have lower titers despite ongoing infection because their damaged stomach lining generates a weaker immune signal.⁴ So resist the urge to read too much meaning into the absolute number. The qualitative result, positive, negative, or equivocal, combined with your clinical history, is what guides the next step.

IgG vs. IgA and IgM Antibodies

You may occasionally see references to IgA or IgM antibody tests for H. pylori. IgM antibodies appear early during a new infection and fade quickly, so in theory an IgM test could help identify recent acquisition of H. pylori. In practice, IgM tests for H. pylori are not reliable enough for clinical use and are rarely ordered. IgA antibodies are present in mucosal secretions and blood, and some studies have explored IgA-based detection, but IgA testing has not demonstrated consistent enough accuracy to replace IgG serology or the active-infection tests. When your doctor orders “H. pylori antibodies,” they almost always mean IgG.

The broader point is that no single antibody class solves the fundamental limitation of serology for H. pylori. The immune system produces antibodies in response to infection, and those antibodies persist even after the infection resolves. To know whether the bacteria are still there, you need a test that looks for the organism itself or its metabolic activity, not the immune footprint it left behind.