A positive H. pylori IgG result means your immune system has produced antibodies against Helicobacter pylori, a bacterium that colonizes the stomach lining. It confirms exposure to the bacterium but does not, on its own, tell you whether the infection is still active or was cleared long ago. That distinction matters because it shapes what your doctor should do next and what risks you actually face.
What the Antibody Test Actually Detects
When H. pylori takes hold in the stomach, the immune system mounts a response that includes producing IgG antibodies. A blood test picks up those antibodies, and a positive result tells you that your body has encountered the bacterium at some point. The problem is that IgG antibodies are persistent. In one study tracking patients for over three and a half years after successful treatment, roughly seven out of ten still tested positive on standard blood serology despite being genuinely cured.1The American Journal of Medicine. Four-year trends in Helicobacter pylori IgG serology following successful eradication So a positive IgG result alone cannot distinguish someone with an active, ongoing infection from someone who was treated years ago and no longer carries the bacterium.
This is why clinicians sometimes describe IgG serology as a “screening” test rather than a definitive diagnostic. Its overall accuracy sits around 86%, compared with about 96% for a urea breath test.2PubMed Central. Reliability of Diagnostic Tests for Helicobacter pylori Infection Where serology shines is its negative predictive value: if your IgG comes back negative, you can be fairly confident you do not have an active infection.3PubMed Central. Diagnosis of Helicobacter pylori infection: serology vs. urea breath test It is the positive results that need further investigation.
Age and False Positives
Accuracy also shifts with age. In younger adults, the specificity of IgG testing is excellent, around 99% for people under 50. But in adults over 65, specificity drops to roughly 75%, meaning about one in four positive results in older people may be false positives.4PubMed Central. Age-Dependent Accuracy of Helicobacter pylori Antibody Assays for Adults, with Special Emphasis on Atrophic Gastritis The main culprit is atrophic gastritis, a condition where the stomach lining thins over time and can develop independently of H. pylori. When researchers excluded patients whose false positives were driven by atrophic gastritis, specificity in the older groups improved to above 93%. If you are over 65 and receive a positive IgG, a follow-up test to confirm active infection is especially important.
What Happens If the Infection Is Active
H. pylori is remarkably adapted to survive in the stomach’s harsh acid bath. The bacterium produces an enzyme called urease that breaks down urea into ammonia, raising the local pH enough to neutralize stomach acid around it.5PubMed. Mechanisms of acid resistance due to the urease system of Helicobacter pylori This ammonia production also changes the physical properties of the stomach’s protective mucus layer, making it less gel-like and easier for the corkscrew-shaped bacterium to swim through.6PubMed Central. Helicobacter pylori moves through mucus by reducing mucin viscoelasticity Once settled beneath the mucus and against the stomach lining, H. pylori can persist for decades if left untreated.
The body does not tolerate this silently. Infection virtually always triggers chronic inflammation of the stomach lining, called chronic active gastritis, with immune cells flooding into the tissue.7PubMed Central. Pathogenesis of Helicobacter pylori Infection – Section: CLINICAL ASPECTS OF H. PYLORI-ASSOCIATED DISEASES Most people with this inflammation never feel a thing. But this low-grade, persistent gastritis is the foundation on which more serious problems can build over years.
Peptic Ulcers and Who Gets Them
The best-known consequence of H. pylori infection is peptic ulcer disease. Infected individuals face a risk of developing ulcers roughly three to ten times higher than uninfected people, and studies have estimated that about 10 to 15% of those carrying H. pylori develop ulcers during long-term follow-up.7PubMed Central. Pathogenesis of Helicobacter pylori Infection – Section: CLINICAL ASPECTS OF H. PYLORI-ASSOCIATED DISEASES That means the majority of infected people never get an ulcer, which raises the question of why some people get sick and others do not.
Part of the answer lies in the bacterial strain itself. H. pylori is not one uniform organism. Some strains carry a set of genes called the cag pathogenicity island, which allows them to inject a protein called CagA directly into stomach cells. Strains carrying this toolkit cause more severe inflammation and raise the risk of both ulcers and cancer compared to strains that lack it.8PubMed. Pathogenesis of Helicobacter pylori-induced gastric inflammation The other part of the answer is the host: your immune response, your genetics, and your lifestyle habits all influence whether chronic gastritis stays quiet or progresses to an ulcer or something worse.
The Cancer Connection
H. pylori was the first bacterium formally recognized as a cause of human cancer.9PubMed. Malignant Helicobacter pylori-Associated Diseases: Gastric Cancer and MALT Lymphoma It is linked to two distinct types of gastric malignancy: adenocarcinoma (the more common form of stomach cancer) and a rare type of lymphoma called gastric MALT lymphoma. The path to cancer typically unfolds over decades. Persistent inflammation damages stomach-lining DNA, and in a small fraction of infected people, that accumulating damage eventually produces malignant cells.
With MALT lymphoma, the story is more specific. The chronic immune stimulation caused by H. pylori can lead to the formation of organized clusters of immune cells in the stomach wall, in tissue that normally does not have them. Over time, B cells in these clusters can begin proliferating abnormally. CagA-positive strains contribute by activating growth-promoting pathways in those B cells and suppressing the tumor-suppressor protein p53, allowing damaged cells to survive when they would ordinarily die.10PubMed Central. Helicobacter pylori Strains and Gastric MALT Lymphoma – Section: 2. GML and Cytotoxin-Associated Gene A (CagA) In early-stage MALT lymphoma, simply eradicating H. pylori is often enough to put the lymphoma into remission, which underscores how dependent the early tumor growth is on the infection itself.
Your genetic background also shapes cancer risk. Certain variations in genes controlling inflammation, particularly those involved in the interleukin signaling pathways, can interact with H. pylori infection and smoking to dramatically amplify the odds of developing stomach cancer.11PLOS ONE. Effects of Interleukin-10 Polymorphisms, Helicobacter pylori Infection, and Smoking on the Risk of Noncardia Gastric Cancer This gene-environment interplay helps explain why gastric cancer rates vary so much across populations and why two people with the same H. pylori infection can face very different outcomes.
Effects Beyond the Stomach
H. pylori’s reach extends beyond the stomach lining. Two blood-related conditions have strong enough links to the infection that international guidelines now list them as reasons to test and treat. The first is unexplained iron deficiency anemia. In one study, H. pylori infection was found in over 60% of patients with iron deficiency anemia that could not be explained by other causes. Patients who received standard H. pylori eradication therapy alongside iron supplements showed significantly greater improvements in hemoglobin and iron stores compared to those given iron alone.12PubMed Central. Helicobacter pylori associated to unexplained or refractory iron deficiency anemia: an Egyptian single-center experience
The second is immune thrombocytopenia, a condition where platelet counts drop because the immune system destroys them. Research has shown that clearing H. pylori in these patients leads to meaningful increases in platelet counts, with one study reporting a roughly twofold to threefold increase from baseline in the year following successful eradication.13Scientific Reports. Helicobacter pylori eradication affects platelet count recovery in immune thrombocytopenia The recognition of these blood-related diseases as indications for H. pylori testing and treatment represents a shift in how clinicians manage them.14PubMed Central. Hematologic manifestations of Helicobacter pylori infection
What to Do After a Positive IgG
If your IgG test comes back positive and you have symptoms, a personal or family history of ulcers, or any of the conditions listed above, the next step is usually a test that detects active infection rather than past exposure. The urea breath test and stool antigen test are the two most commonly recommended options. Both detect the presence of live H. pylori rather than lingering antibodies.15PubMed. Diagnosis of Helicobacter pylori: invasive and non-invasive tests Positive serology followed by a positive breath test or stool antigen test is strong evidence that you have an active infection worth treating.
One practical point that often gets missed: proton pump inhibitors, the acid-reducing medications many people take for heartburn, can cause false-negative results on breath tests and stool antigen tests. If you are taking a PPI, your doctor will typically ask you to stop it for at least two weeks before running a confirmatory test. Antibiotics and bismuth-containing products (like Pepto-Bismol) can also suppress H. pylori enough to produce a misleading negative result.
A global review of clinical guidelines found that the most frequently recommended reasons to test and treat H. pylori include active peptic ulcer disease, long-term use of NSAIDs like aspirin, and gastric MALT lymphoma. About 40% of reviewed guidelines went further, recommending eradication whenever H. pylori infection is confirmed, regardless of symptoms.16PubMed Central. A scoping review of worldwide guidelines for diagnosis and treatment of Helicobacter pylori infection This “test-and-treat-all” philosophy reflects the view that even asymptomatic infection carries long-term risks, though not every guideline has adopted it.
How Treatment Works and When It Fails
Standard first-line treatment for H. pylori involves a combination of antibiotics and an acid-suppressing medication, taken for 10 to 14 days. The regimens usually involve two or three antibiotics because single-drug approaches fail at unacceptably high rates. The bacterium sits beneath the stomach’s mucus layer, which limits how much drug can reach it, and antibiotic resistance is a growing global problem.
Resistance to clarithromycin, one of the most commonly used antibiotics in H. pylori treatment, is the single biggest predictor of treatment failure. A meta-analysis found that clarithromycin resistance had a larger impact on cure rates than resistance to metronidazole, another frequently used drug. Quadruple-therapy regimens that combine multiple antibiotics with bismuth remain effective in over 80% of cases, even when resistance to one of the antibiotics is present.17PubMed. Meta-analysis: the effect of antibiotic resistance status on the efficacy of triple and quadruple first-line therapies for Helicobacter pylori
If the first round fails, choosing the next regimen works best when guided by susceptibility testing, which identifies which antibiotics the particular strain is vulnerable to. When that testing is not available, an acceptable alternative is simply avoiding the antibiotics that were already used. The key principle is not to repeat clarithromycin or levofloxacin if they were part of a failed course.18PubMed Central. Treatment of Refractory Helicobacter pylori Infection-Tailored or Empirical Therapy – Section: OPTIMIZATION OF THIRD-LINE TREATMENT
Why Serology Is Useless After Treatment
Here is a point that trips up many patients and even some clinicians: you cannot use IgG blood tests to check whether treatment worked. Because H. pylori-specific antibodies can remain detectable indefinitely after successful eradication, a post-treatment blood test may still read positive even though the bacterium is gone.19PubMed Central. Clinical Rationale for Confirmation Testing After Treatment of Helicobacter pylori Infection: Implications of Rising Antibiotic Resistance – Section: Serology This is the same persistence of antibodies discussed earlier, and it means that confirming cure requires a test that detects live organisms, not immune memory.
Doctors typically wait at least four weeks after finishing antibiotics (and at least two weeks after stopping a PPI) before running a breath test or stool antigen test to confirm eradication. Checking too early risks a false negative, because antibiotics may have suppressed the bacterium without fully eliminating it.
How H. pylori Spreads and Whether Reinfection Is Common
H. pylori is predominantly acquired in childhood, most likely through person-to-person contact. Studies have linked infection to overcrowding, lower socioeconomic conditions, and sharing a bed as a child.20BMJ. Relation between infection with Helicobacter pylori and living conditions in childhood: evidence for person to person transmission in early life The rising prevalence seen with older age in population surveys largely reflects a cohort effect: people born in earlier decades were more likely to be infected as children because of more crowded living conditions, not because adults keep acquiring new infections throughout life.
Reinfection after successful treatment is uncommon in developed countries. Most apparent “reinfections” that show up within the first couple of years are actually recrudescence, meaning the original infection was never fully cleared and slowly rebounded. In patients whose breath test stayed negative for a full year after treatment, the true reinfection rate was less than half a percent per year.21QJM: An International Journal of Medicine. Reinfection or recrudescence after apparently successful eradication of Helicobacter pylori infection: implications for treatment of patients with duodenal ulcer disease This is reassuring: once you have genuinely cleared the infection and confirmed it, the odds of catching it again are low.
The Flip Side of Eradication
An ongoing and genuinely complicated debate in the research community is whether wiping out H. pylori across whole populations might have unintended consequences. Some epidemiological data show that H. pylori infection is inversely associated with conditions like allergic asthma, gastroesophageal reflux disease (GERD), and Barrett esophagus. Concerns have been raised that widespread eradication campaigns, while reducing ulcers and gastric cancer, could contribute to rising rates of these conditions.22PubMed Central. The Protective Effects of Helicobacter pylori Infection on Allergic Asthma – Section: Treatment of Asthma Related to H. pylori Infection There is also the practical worry about antibiotic resistance: mass eradication means mass antibiotic use, which accelerates resistance not only in H. pylori itself but in other bacteria too.
None of this changes the calculation for an individual patient who has a confirmed active infection and symptoms or risk factors. The benefits of eradication for people with ulcers, MALT lymphoma, unexplained iron deficiency anemia, or a family history of gastric cancer are well established. But it does add nuance to the “treat everyone who tests positive” approach and helps explain why guidelines worldwide have not reached full consensus on universal eradication. For now, if your IgG test comes back positive, the most useful next step is a conversation with your doctor about whether your symptoms and history warrant confirmatory testing, and from there, a clear plan for treatment if the infection turns out to be active.