H. Pylori Antibody IgG Test

About half the world's population carries Helicobacter pylori, a bacterium that burrows into the stomach lining and, left untreated, can cause ulcers, chronic inflammation, and the precancerous changes that precede gastric cancer. Most people with the infection never feel a thing. An H. pylori IgG (immunoglobulin G) antibody test is one of the simplest ways to find out whether your immune system has encountered this bacterium, using a standard blood draw with no fasting, no breath collection, and no stool sample.

What makes this test especially valuable for prevention is its sensitivity. In large studies, IgG serology (blood-based antibody testing) catches more than 90% of people who have been infected, making it an effective first screen. The trade-off is that a positive result tells you your immune system has seen H. pylori at some point, but it cannot tell you, on its own, whether the infection is still active right now or was cleared years ago. That distinction matters for deciding next steps, and this article will walk you through it.

What This Test Actually Measures

When H. pylori colonizes your stomach, your immune system responds by producing IgG antibodies, a class of immune proteins that circulate in your blood and represent your body's long-term memory of the infection. This test uses an ELISA (enzyme-linked immunosorbent assay) technique to measure the concentration of those specific antibodies in your blood sample.

A key feature of IgG is its persistence. These antibodies appear roughly three weeks after infection and can remain detectable for months to years after the bacterium has been eradicated. In a Japanese cohort of over 55,000 adults, IgG titers (antibody levels) dropped significantly within one year of successful treatment (from a median of 34 to 7.9 U/mL), but about 41% of people still tested positive more than a year later. This slow antibody decay is why IgG works well as a screening tool for lifetime exposure but poorly as a standalone test for confirming that treatment worked.

In a Yemeni study of 200 adults classified by both IgG and stool antigen testing, the combination revealed distinct infection categories: about 40.5% were positive on both tests (active chronic infection), 38% were IgG positive only (chronic or past infection), and 13.5% were stool antigen positive only (likely acute, recent infection). This pattern illustrates why a single IgG result benefits from a companion test to clarify your current infection status.

Gastric Cancer Risk

The strongest and most consistent outcome linked to H. pylori IgG seropositivity (testing positive for the antibody) is gastric cancer, particularly cancers of the lower stomach (the non-cardia region). In the China Kadoorie Biobank, a large prospective study using sensitive antibody testing, people with confirmed H. pylori infection had about six times the risk of non-cardia gastric cancer and about three times the risk of upper-stomach (cardia) gastric cancer compared with uninfected individuals. The researchers estimated that roughly 79% of non-cardia cases and 63% of cardia cases in the study population were directly attributable to the infection.

The risk signal gets even clearer when antibodies to specific bacterial proteins are measured alongside general IgG. In a combined analysis of Chinese and European data, people who tested positive for multiple harm-related bacterial proteins, known as virulence factors (including CagA, HP1564, and HP0305), had about 5.6 times the risk of non-cardia gastric cancer compared with those positive for CagA alone. This means the type of H. pylori strain you carry matters, not just whether you carry it.

The China Kadoorie Biobank and other prospective studies with long follow-up consistently show that the association between H. pylori and gastric cancer strengthens when blood samples are drawn many years before diagnosis. This long latency is precisely why screening with IgG years before symptoms develop has the most preventive value.

If you test positive, the actionable question is whether eradication therapy can reduce your future gastric cancer risk. A pooled analysis of large Japanese cohorts found that among people who were H. pylori positive and had atrophic gastritis (a condition where the stomach lining thins and loses its normal acid-producing cells), successful eradication with at least six years of follow-up reduced gastric cancer risk by more than half (about 56% reduction).

Heart Disease Risk

The link between H. pylori and cardiovascular disease is real but much more modest than the gastric cancer connection. A meta-analysis of 41 cohort studies covering over 230,000 people found that H. pylori infection (mostly detected by IgG serology) was associated with about a 10% higher risk of cardiovascular disease and coronary heart disease. A separate Mendelian randomization study, a research method that uses genetic variation to test whether a relationship is truly causal, supported a similarly modest causal link: genetically higher anti-H. pylori IgG levels were associated with about a 10% increase in heart attack risk.

The mechanism may involve metabolic disruption. The Mendelian randomization data linked higher H. pylori IgG to lower HDL cholesterol (the "good" cholesterol), and a NHANES-based study of nearly 9,400 adults found that the cardiovascular risk was concentrated in people who were both H. pylori positive and had high insulin resistance. In that subgroup, all-cause mortality was about 23% higher. For people without metabolic risk factors, the cardiovascular signal from H. pylori seropositivity alone appears weak.

Pregnancy Complications

In a study of 1,372 European women across three birth cohorts, H. pylori seropositivity was associated with a higher likelihood of experiencing two or more adverse pregnancy outcomes (about 32% higher odds). The strongest signal came from antibodies to specific bacterial outer membrane proteins, where positive women had roughly double the odds of multiple complications. Among women of Western European origin specifically, seropositivity was linked to about a 3.4-fold higher risk of hypertensive disorders during pregnancy.

Mendelian randomization data further support a causal relationship: genetically predicted higher H. pylori IgG was associated with about a 12% increase in risk of preeclampsia and a 17% increase in risk of premature rupture of membranes. If you are planning a pregnancy or are in early pregnancy, knowing your H. pylori status could flag a modifiable risk factor worth discussing with your care team.

Other Cancer Associations

Beyond the stomach, there is weaker evidence linking H. pylori to colorectal cancer. In the large European EPIC cohort (485 cases, 485 controls), H. pylori seropositivity was associated with about a 36% higher odds of colorectal cancer, driven by antibodies to specific bacterial proteins (HcpC and VacA). However, a Mendelian randomization analysis found no causal effect of H. pylori IgG on colorectal cancer risk, suggesting the observational association may reflect shared risk factors rather than a direct biological pathway.

A Japanese cohort of about 5,000 adults followed for eight years found that H. pylori antibody positivity was associated with 59% higher overall cancer incidence but no difference in cancer mortality. This pattern suggests that H. pylori may increase the chance of a cancer diagnosis without necessarily worsening outcomes once diagnosed, though more data are needed.

How Accurate Is This Test?

Performance varies meaningfully by assay brand and population. Here is a snapshot from published validation studies:

The pattern is consistent: IgG serology is excellent at catching people who have been infected (high sensitivity) but less precise at ruling out false positives, especially in older adults, people with gastric atrophy, or those who have been previously treated. This is why a positive IgG result should prompt a confirmatory test such as a stool antigen test or urea breath test before starting treatment.

When Results Can Be Misleading

The single most common source of misinterpretation is treating a positive IgG as proof of active, current infection. IgG can stay positive for years after the bacterium has been cleared, whether through treatment or spontaneous resolution. If you have been treated for H. pylori in the past, a positive IgG does not mean treatment failed.

• Prior eradication therapy: IgG titers fall after successful treatment but often remain above the positive cutoff for a year or more. One study found specificity for detecting treatment failure was as low as 22 to 24% using a single post-treatment IgG. Use stool antigen or breath testing to confirm eradication, not IgG alone.
• Assay and kit differences: Sensitivity ranges from about 60% to nearly 100% across commercial kits, and cutoff values differ by manufacturer and population. Results from one lab's kit are not directly comparable to another's.
• Borderline titers: Values near the positive/negative cutoff (for example, 3 to 10 U/mL on certain assays) have high rates of misclassification. If your result falls in this gray zone, a confirmatory test is especially important.
• Chronic NSAID use: In people taking non-steroidal anti-inflammatory drugs long-term, several IgG assays show reduced specificity (more false positives), likely because NSAIDs cause a type of stomach inflammation that keeps antibody levels elevated even when bacterial load is low.

H. pylori IgG does not fluctuate with meals, time of day, exercise, or short-term illness. It is a stable, slowly changing marker, which means you do not need to fast or time your blood draw. The confounders that matter are long-term: your treatment history, the specific lab kit used, and whether you have advanced stomach lining changes.

Reference Ranges

There are no universal clinical cutpoints for H. pylori IgG because results depend heavily on the specific assay your lab uses. Each commercial kit defines its own positive, negative, and equivocal ranges. The numbers below are drawn from commonly used assays in published research and are meant to orient you, not to replace the reference range printed on your lab report.

Always compare your results within the same lab and the same assay over time. Switching labs or kit brands between tests makes trend comparisons unreliable.

Who Gets Infected and How Common Is It?

H. pylori is one of the most common chronic infections worldwide, usually acquired in childhood through person-to-person contact or contaminated water. Seroprevalence surveys (population-level antibody testing) using IgG show striking numbers: about 57% of Hispanic/Latino adults in the US test positive, about 44% of asymptomatic Korean adults, and nearly two-thirds of asymptomatic patients in a US safety-net healthcare system. Rates are consistently higher in older adults, men, people born outside the US, smokers, and those from lower socioeconomic backgrounds.

These numbers mean that even if you feel perfectly healthy, the probability of a positive IgG is far from trivial, especially if you belong to a higher-prevalence group. Screening catches infections that would otherwise go undetected until they cause damage.

Tracking Your Trend

A single H. pylori IgG result gives you a yes-or-no answer about exposure, which is useful but incomplete. Serial testing adds a dimension that a single draw cannot: the trajectory of your antibody titer. A declining titer over six to twelve months after treatment suggests successful eradication, even if the result remains technically positive. Research shows that a drop of 25% or more at about six months is a reliable signal of clearance.

If you have never been treated and your baseline is positive, the next step is to confirm active infection with a stool antigen test or urea breath test, then pursue eradication if confirmed. After treatment, retest with stool antigen or breath test at four to six weeks (the standard confirmation window), and consider a follow-up IgG at six to twelve months to verify the titer is trending down. For people at higher gastric cancer risk (family history, prior precancerous stomach changes, certain ethnic backgrounds), an annual or biannual recheck gives you ongoing reassurance that you remain clear.

What to Do With Your Result

If your IgG is negative, you most likely have not been infected. No further testing is needed unless you have unexplained stomach symptoms, in which case a stool antigen test can catch very recent infections that IgG has not yet responded to.

If your IgG is positive and you have never been treated, order a stool antigen test or urea breath test to confirm active infection. If active infection is confirmed, standard eradication therapy (a combination of a proton pump inhibitor, a medication that reduces stomach acid, and antibiotics, prescribed by a physician) is the next step. If you have risk factors for gastric cancer, such as a family history, East Asian ancestry, or a prior finding of stomach lining changes, consider a referral to a gastroenterologist for an upper endoscopy, which can directly visualize and biopsy the stomach lining for precancerous changes.

If your IgG is positive but you have been treated in the past, do not assume the infection has returned. Confirm with a stool antigen test or breath test. If those are negative, your positive IgG is simply residual immune memory, not a sign of failure.

For anyone with a confirmed positive, the broader workup should include a standard metabolic panel to check for the metabolic disruptions (lipid changes, insulin resistance) that research links to chronic H. pylori infection. If you are pregnant or planning pregnancy, share your result with your obstetrician, given the associations with preeclampsia and other complications.