H. pylori Antibody Testing: When to Use IgG, IgA, and IgM
Do not use serological antibody tests (IgG, IgA, or IgM) as your primary diagnostic method for H. pylori infection—instead, use urea breath test (UBT) or laboratory-based monoclonal stool antigen test, which detect active infection with 93-97% accuracy. 1, 2
Why Serology Tests Are Not Recommended for Routine Diagnosis
Serological tests cannot distinguish between active infection and past exposure because antibody levels persist in blood for long periods after eradication, leading to false-positive results in previously treated patients with an overall accuracy averaging only 78% (range 68-82%). 3, 1
Serology should never be used to confirm eradication after treatment as antibodies remain elevated after H. pylori elimination, making them clinically useless for this purpose. 1, 4
The positive predictive value of serology falls dramatically in populations with low disease prevalence, further limiting clinical utility. 1
Specific Performance of Different Antibody Types
IgG Antibodies
IgG testing is the only antibody test with acceptable performance, showing sensitivity of 94.7-98% and specificity of 71-94% in research studies. 5, 6
IgG serology may be useful in limited situations: when patients have recently used antibiotics, bismuth, or PPIs (which cause false-negative results with other tests), or in patients with gastric atrophy, gastric malignancies, or ulcer bleeding where bacterial load is low. 1, 4
IgA Antibodies
IgA testing has unacceptably low specificity (59-73%) and adds no diagnostic value over IgG testing alone. 5, 6
While IgA sensitivity can reach 93-97%, the poor specificity makes it clinically unreliable, and using panels of IgG, IgA, and IgM provides no added benefit over validated IgG tests alone. 1, 6
Some IgA-positive but IgG-negative results occur in approximately 5% of patients, but this does not justify routine IgA testing given the high false-positive rate. 6
IgM Antibodies
IgM testing has limited clinical utility, with prevalence of only 10.4% in symptomatic patients and 1.1% in asymptomatic individuals. 7
IgM may theoretically indicate acute infection, but this distinction has no practical clinical value since treatment decisions are based on presence of infection regardless of timing. 7
IgM testing is not FDA-approved or recommended by any major guideline society for routine clinical use. 1
Recommended Testing Algorithm
For Initial Diagnosis in Primary Care (<50 years, no alarm symptoms)
First choice: 13C-urea breath test (UBT) with sensitivity 94-97% and specificity 95-97.7%, requiring 6-hour fast before testing. 1, 2, 4
Alternative: Laboratory-based monoclonal stool antigen test with sensitivity and specificity of 93%—avoid rapid in-office immunochromatographic versions which have significantly lower accuracy. 1, 2
For Patients Requiring Endoscopy (≥50 years, alarm symptoms, or treatment failure)
Perform rapid urease test (sensitivity 80-95%, specificity 95-100%) plus histology during endoscopy. 2, 4
Consider culture for antimicrobial susceptibility testing, especially after treatment failure when resistance is suspected. 2, 4
For Confirmation of Eradication
- Use UBT or stool antigen test at least 4 weeks after completing treatment—never use serology. 1, 2, 4
Critical Medication Washout Periods
Stop proton pump inhibitors for at least 2 weeks before testing with UBT, stool antigen, rapid urease test, histology, or culture to avoid false-negative results. 1, 2, 4
Stop antibiotics and bismuth for at least 4 weeks before testing to prevent false-negative results. 1, 2
Serology is the only test not affected by these medications, which is its sole potential advantage in patients who cannot stop these drugs and clinical suspicion remains high. 1
Common Pitfalls to Avoid
Never use rapid in-office serological tests—they have limited accuracy and should be avoided entirely. 1
Do not order panels of IgG, IgA, and IgM tests—they provide no added benefit and may include non-FDA-approved tests of unclear diagnostic value. 1
Remember that serology may be falsely positive in patients with intestinal metaplasia even when H. pylori has been eradicated, further limiting its clinical utility. 6