Helicobacter pylori Ag / IgG / IgM Tests
🦠 Helicobacter pylori Antigen (Ag), IgG, and IgM Tests — Complete Guide
Diagnosis, ICA/CLIA/ELISA Methods, Reference Ranges, Interpretation Tips, and Clinical Significance
📝 Meta Description
A complete guide to Helicobacter pylori antigen (Ag), IgG, and IgM tests, including diagnostic purpose, ICA/CLIA/ELISA methods, reference ranges, interpretation points, and clinical implications for gastric diseases.
🦠 Helicobacter pylori Antigen (Ag), IgG, and IgM Tests: Complete Medical Guide
Helicobacter pylori (H. pylori) is a gram-negative bacterium that colonizes the gastric mucosa and is strongly associated with chronic gastritis, peptic ulcer disease, MALT lymphoma, and gastric cancer.
H. pylori infection is diagnosed using both antigen tests (Ag)—which detect active infection—and antibody tests (IgG, IgM)—which suggest current or past infection.
This guide reviews the purpose, methods (ICA, CLIA, ELISA), interpretation, reference ranges, and clinical significance.
1. Purpose of H. pylori Testing
✔ Detect current H. pylori infection
✔ Evaluate risk of peptic ulcer disease or gastric cancer
✔ Monitor response to eradication therapy (Ag test preferred)
✔ Assist in the evaluation of dyspepsia or chronic gastritis
✔ Screen high-risk patients for gastric cancer prevention
2. Test Methods (Ag / IgG / IgM)
🔬 1) ICA (Immunochromatographic Assay)
A rapid test for detecting stool antigen (Ag) or serum IgG/IgM.
Characteristics
- Results within 10–15 minutes
- Simple POC (point-of-care) method
- Useful for initial screening
Pros
✔ Fast, inexpensive
✔ Easy to perform
Cons
✖ Lower sensitivity/specificity vs. laboratory methods
✖ False negatives with recent treatment or PPI use
🔬 2) CLIA (Chemiluminescent Immunoassay)
A widely used automated method for IgG and IgM quantification.
Characteristics
- High sensitivity and specificity
- Provides quantitative/semiquantitative values
- Standard method in clinical laboratories
Pros
✔ Reliable & reproducible
✔ Suitable for follow-up testing
✔ Lower false results than ICA
🔬 3) ELISA (Enzyme-linked Immunosorbent Assay)
A traditional and well-validated method for detecting IgG and IgM antibodies.
Characteristics
- Excellent accuracy
- Suitable for high-volume testing
- IgG remains positive long after treatment → limited for follow-up
3. Characteristics of Each Test
📌 A) H. pylori Antigen (Ag) Test
Best marker for active infection.
Commonly performed using stool antigen tests (ICA or EIA).
Important Points
- False negatives if taking PPI, antibiotics, bismuth → stop for 2 weeks before testing
- Best method for confirming eradication therapy (after ≥4 weeks)
📌 B) H. pylori IgG
- Indicates past or current infection
- IgG persists for months to years, even after eradication
→ Not suitable for assessing treatment success - Useful for screening
📌 C) H. pylori IgM
- May indicate early infection
- Lower sensitivity/specificity
→ Not recommended as a standalone diagnostic marker
4. Reference Ranges
| Test | Normal (Negative) | Positive Criteria |
|---|---|---|
| Antigen (Ag) | Not detected | Detected (+) |
| IgG | Below cut-off | At or above cut-off |
| IgM | Below cut-off | At or above cut-off |
⚠ Cut-off values vary by platform (ICA, CLIA, ELISA).
⚠ IgG positivity does not necessarily mean active infection.
5. Clinical Significance & Related Conditions
🩺 Conditions associated with H. pylori infection
- Chronic superficial gastritis
- Atrophic gastritis
- Gastric and duodenal ulcers
- MALT lymphoma
- Gastric cancer (IARC Group 1 carcinogen)
- Functional dyspepsia
- Unexplained iron-deficiency anemia
😷 Interpretation
🔹 1) Antigen (Ag) Positive
→ Indicates active infection
→ Requires eradication therapy
→ Retesting recommended ≥4 weeks after treatment
🔹 2) IgG Positive
→ Past or present infection
→ Not reliable for treatment confirmation
→ Evaluate PPI use, symptoms, and endoscopic findings
🔹 3) IgM Positive
→ Possible early infection
→ Low specificity → requires confirmation with IgG or Ag test
🔹 4) Ag(-) + IgG(+)
→ Likely past infection
→ Could be false negative Ag due to medications
→ Review PPI/antibiotic use
6. Important Interpretation Considerations
✔ 1) Antibody dynamics after treatment
IgG remains elevated long-term → do not use to confirm eradication.
✔ 2) PPI, antibiotics, or bismuth increase false negatives
Stop for at least 2 weeks before stool antigen test.
✔ 3) Acute GI bleeding can decrease Ag test accuracy
✔ 4) IgM alone is unreliable
Always reassess with IgG or Ag.
✔ 5) Antibody tests are less accurate in children
Prefer Ag test or urea breath test.
7. Summary: Which Test Should You Choose?
| Test | Strengths | Limitations | Recommended Use |
|---|---|---|---|
| Antigen (Ag) | Best for active infection & post-treatment confirmation | Affected by PPI/antibiotics | First-line test; eradication assessment |
| IgG | Good screening tool | Cannot confirm active infection | Initial evaluation |
| IgM | May indicate early infection | Low sensitivity/specificity | Limited use; supplementary testing |
8. References
- Chey WD et al. ACG Clinical Guideline: Treatment of H. pylori Infection. Am J Gastroenterol.
- Malfertheiner P et al. Maastricht VI/Florence Consensus Report. Gut.
- Korean Society for Laboratory Medicine. Guidelines for Infectious Serology Testing.
- Megraud F. Diagnosis of H. pylori Infection: ELISA, CLIA, and Antigen Tests. Clin Microbiol Rev.
- WHO IARC Monographs: Helicobacter pylori and Gastric Cancer.