What is the preferred test for diagnosing active Helicobacter pylori infection in an adult who is not taking proton‑pump inhibitors, H2‑blockers, antibiotics, or bismuth?

Preferred Test for Active H. pylori Infection

The urea breath test (UBT) or laboratory-based monoclonal stool antigen test are the preferred first-line diagnostic methods for detecting active H. pylori infection in adults not taking PPIs, antibiotics, or bismuth. 1, 2

Why These Tests Are Preferred

Urea Breath Test (UBT)

• The 13C-UBT is considered the most accurate non-invasive test available, with sensitivity of 94.7-97% and specificity of 95-97.7% 2, 3
• The test detects active infection only, not past exposure, making it ideal for confirming current bacterial presence 1, 2
• It is unaffected by patchy distribution of H. pylori in the stomach, unlike biopsy-based methods that can miss infection due to sampling error 4
• The 13C version is non-radioactive and safe for all populations, including children and pregnant women 3

Laboratory-Based Monoclonal Stool Antigen Test

• This test achieves comparable accuracy to UBT, with sensitivity and specificity of approximately 93% 1, 2
• It directly detects H. pylori bacterial antigens in stool, confirming active infection rather than just antibody response 1, 5
• The test is more practical and cost-effective than endoscopy while maintaining excellent diagnostic performance 2

Tests to Avoid

Serology (Blood Tests)

• Serology is generally not recommended and not reimbursed by Medicare 1
• These tests cannot distinguish between active infection and past exposure, as antibodies persist long after eradication (creating a "serologic scar") 1, 2
• The overall accuracy of commercial ELISA serology averages only 78% (range 68-82%), which is inadequate for clinical use 1, 2
• Serology should never be used to confirm eradication after treatment 1, 2

Limited exceptions where serology may be considered: when patients cannot stop PPIs/antibiotics and testing cannot be delayed, or in gastric atrophy, malignancy, or ulcer bleeding where bacterial load is very low 2

Rapid In-Office Tests

• Rapid in-office serological tests and immunochromatographic stool tests have limited accuracy and should be avoided 2
• Only laboratory-based monoclonal antibody stool tests achieve high diagnostic performance 2, 6

Critical Medication Considerations

Since your patient is not taking interfering medications, you can proceed directly with testing. However, be aware that:

• PPIs must be stopped for at least 2 weeks before UBT or stool antigen testing, as they cause 10-40% false-negative rates by reducing bacterial load 1, 2, 6
• Antibiotics and bismuth must be stopped for at least 4 weeks before testing 1, 6
• H2-receptor antagonists do not affect bacterial load and can be substituted if acid suppression is needed 1, 2

Practical Algorithm for Test Selection

For your patient (adult, no interfering medications):

1. First choice: 13C-urea breath test - highest accuracy, no sampling error, widely available 2, 3

2. Equally acceptable alternative: Laboratory-based monoclonal stool antigen test - comparable accuracy, may be more convenient or cost-effective in some settings 2, 5

3. Do NOT use: Serology, rapid in-office tests, or IgA/IgM antibody panels 1, 2

Common Pitfalls to Avoid

• Never order serology panels (IgG/IgA/IgM) - they provide no added benefit over validated IgG alone and often include non-FDA-approved tests of unclear value 1
• Specify "laboratory-based monoclonal" when ordering stool antigen tests - rapid in-office versions have significantly lower accuracy 2, 6
• Do not test patients currently on PPIs unless you deliberately choose serology or can wait 2 weeks after stopping the medication 2, 6
• A positive result on any test (UBT or stool antigen) can be trusted even if medication washout was incomplete, as these medications only cause false-negatives, never false-positives 6