What this test measures
Helicobacter pylori is the bacterium that colonises the stomach lining and causes chronic gastritis, peptic ulcers, and (rarely) gastric cancer and MALT lymphoma. IgA antibodies are produced locally at mucosal surfaces and circulate in low concentrations in serum. The IgA assay measures these antibodies as an alternative or adjunct to the more sensitive IgG antibody.
IgA is considered less sensitive than IgG for diagnosis but may be useful in IgG-equivocal cases or in young patients. Modern guidelines prefer non-invasive active-infection tests (urea breath test, stool antigen) over antibody testing in most situations, because antibodies persist after eradication and cannot distinguish active from past infection.
Why it matters
In India, H. pylori prevalence is high — up to 60–80% of adults have evidence of past or current infection. Most are asymptomatic, but H. pylori causes the majority of peptic ulcer disease in non-NSAID users. Eradication relieves dyspepsia, heals ulcers, and significantly reduces gastric cancer risk in high-incidence populations.
The IgA antibody is most useful as an adjunct to IgG in evaluating chronic dyspepsia and atypical symptoms. For diagnosis of active infection, the urea breath test or stool antigen is preferred. For test-of-cure after eradication therapy, antibody tests are NOT suitable — use urea breath test or stool antigen 4–6 weeks after completing treatment.
How to prepare
No fasting required. Continue all medications. Antibody tests are not affected by proton-pump inhibitors (unlike breath and stool antigen tests). Stop biotin supplements 48 hours before testing as they can interfere with some immunoassays.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| H. pylori IgA (Index / U/mL)[1][2][3] | Negative (assay-specific cut-off) | Negative: low likelihood of current or past mucosal H. pylori infection. Does not exclude infection in early disease or in patients with poor mucosal IgA production. If clinical suspicion remains, perform urea breath test or stool antigen. | Positive: supports H. pylori exposure — current or past infection. Cannot distinguish active from healed infection (antibodies persist for months to years after eradication). Confirm active infection with urea breath test or stool antigen before starting eradication therapy. |
H. pylori test choice by clinical question
| Question | Best test |
|---|---|
| Is there active H. pylori infection? | Urea breath test or stool antigen |
| Has the patient ever been exposed? | IgG / IgA antibody |
| Did the treatment work? (test of cure) | Urea breath test or stool antigen, 4–6 weeks after treatment |
| Need biopsy at endoscopy anyway? | Rapid urease test + histology |
Frequently asked questions
Why is the urea breath test or stool antigen preferred over antibody?
Active-infection tests (urea breath, stool antigen) tell you whether the bacterium is in the stomach right now. Antibody tests tell you whether the immune system has ever seen H. pylori — they can stay positive for months to years after successful eradication.
When is the IgA test useful?
As an adjunct to IgG in suspected H. pylori where IgG is equivocal, in patients with mucosal antibody responses (rare clinical scenarios), and in some research and epidemiological studies. It is rarely a stand-alone test.
Can I be tested while on a proton-pump inhibitor (PPI)?
Yes — antibody tests are not affected by PPIs. (Urea breath and stool antigen tests can give false negatives on PPIs; you need to stop the PPI for 2 weeks before those tests.)
How is H. pylori treated?
Standard "triple therapy" is a PPI plus two antibiotics (amoxicillin + clarithromycin) for 14 days, or "quadruple therapy" (PPI + bismuth + tetracycline + metronidazole) in areas with high clarithromycin resistance — which now includes much of India. Always confirm cure 4–6 weeks later.
Will the IgA become negative after treatment?
Eventually, over months to years — but slowly and unpredictably. Antibody tests should NOT be used to confirm cure. Use urea breath test or stool antigen 4–6 weeks after treatment.
Should everyone with positive H. pylori be treated?
Indications for treatment include peptic ulcer disease, MALT lymphoma, dyspepsia, family history of gastric cancer, long-term NSAID or aspirin use, iron-deficiency anemia of unclear cause, and ITP. Asymptomatic colonisation without these risks is not routinely treated — discuss with your doctor.
Related Immunology tests
Tests commonly ordered alongside HELICOBACTER PYLORI - IgA, or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Helicobacter pylori · accessed 2026-05-30T00:00:00.000Z
- ACG Guideline — Treatment of Helicobacter pylori Infection · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — H. pylori Tests · accessed 2026-05-30T00:00:00.000Z
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