What are the recommended tests and treatments for Helicobacter pylori (H. pylori) and Giardia infections?

Diagnostic Testing for H. pylori and Giardia Infections

For H. pylori detection, the urea breath test (UBT) or stool antigen test are the preferred non-invasive diagnostic methods due to their high sensitivity and specificity, while for Giardia, stool antigen testing is the recommended approach. 1, 2

H. pylori Diagnostic Testing

Non-Invasive Tests (First-Line)

• Urea Breath Test (UBT): The most accurate non-invasive test with excellent sensitivity (94.7-97%) and specificity (95-95.7%), detecting active infection rather than past exposure 3, 1, 2

• Stool Antigen Test: Directly detects H. pylori bacterial antigens in stool with sensitivity and specificity of approximately 93%, comparable to UBT 3, 1, 4

• Serology Tests: Not recommended as primary diagnostic method as they cannot distinguish between active infection and past exposure (antibodies persist for long periods after eradication), with accuracy averaging only 78% 3, 1

Invasive Tests (When Endoscopy is Indicated)

• Rapid Urease Test: Provides quick results during endoscopy with good sensitivity and specificity 3, 1

• Histology: Allows visualization of bacteria and assessment of mucosal damage 3, 1

• Culture: Permits antimicrobial susceptibility testing, especially valuable after treatment failure 3, 5

Important Testing Considerations for H. pylori

• Stop medications before testing: Proton pump inhibitors should be discontinued at least 2 weeks before testing, and antibiotics/bismuth for at least 4 weeks before testing to avoid false-negative results 3, 1

• Confirmation of eradication: Should be performed using UBT or stool antigen test no earlier than 4 weeks after completion of treatment 1

• Indications for endoscopy: Patients with alarm symptoms (bleeding, weight loss, dysphagia, palpable mass), older patients (≥50 years) with new-onset dyspepsia, or patients who have failed eradication therapy 1

Giardia Diagnostic Testing

• Stool antigen testing: The preferred method for diagnosing Giardia infection with high sensitivity and specificity 6

• Multiple stool samples: May be required (typically three samples collected on alternate days) to increase diagnostic yield due to intermittent shedding of the parasite 7

• Direct microscopic examination: Traditional method that requires expertise but can identify Giardia cysts or trophozoites in stool samples 7, 6

Testing Algorithm

1. For patients <50 years with dyspeptic symptoms and no alarm features:

   • Use non-invasive "test and treat" strategy with UBT or stool antigen test for H. pylori 3, 1
   • For Giardia suspicion, order stool antigen test 6

2. For patients ≥50 years or with alarm symptoms:

   • Proceed with endoscopy and invasive testing for H. pylori 1
   • Collect stool samples for Giardia testing 7, 6

3. For confirmation of H. pylori eradication:

   • Use UBT or stool antigen test at least 4 weeks after treatment completion 3, 1

Pitfalls to Avoid

• Using serology as the primary diagnostic method for H. pylori or to confirm eradication 3, 1
• Testing for H. pylori while patient is on PPIs, antibiotics, or bismuth compounds 3, 1
• Relying on a single stool sample for Giardia diagnosis 7
• Using rapid in-office serological tests for H. pylori due to their limited accuracy 1