What is the preparation required for an H. pylori test?

Preparation for H. pylori Testing

For accurate H. pylori testing, patients must fast for at least 6 hours before the test and discontinue proton pump inhibitors (PPIs) for at least 7 days, antibiotics and bismuth compounds for at least 4 weeks, and H2-receptor antagonists for at least 24 hours prior to testing. 1

Types of H. pylori Tests

There are two main categories of tests for H. pylori:

Non-invasive Tests (No Endoscopy Required)

1. Urea Breath Test (UBT)

   • Considered the gold standard for active H. pylori infection diagnosis
   • Uses labeled urea (13C or 14C) metabolized by H. pylori
   • Sensitivity and specificity >90%
   • Requires fasting for at least 6 hours

2. Stool Antigen Test (SAT)

   • Comparable accuracy to UBT (sensitivity and specificity >90%)
   • Requires proper laboratory processing
   • Needs an acorn-sized stool sample

3. Serology

   • Not recommended for confirming eradication after treatment
   • May remain positive for months after successful eradication
   • Takes up to six months for antibody titers to fall by 50% after successful treatment 2

Invasive Tests (Requiring Endoscopy)

1. Rapid Urease Test (RUT)

   • Based on H. pylori urease enzyme activity
   • Sensitivity 80-95%, specificity 95-100% in pretreatment settings 2

2. Histological Examination

   • Requires gastric biopsies (at least two from antrum and body)
   • Various staining methods available (modified Giemsa recommended) 2

3. Culture and Susceptibility Testing

   • Recommended after two failed treatment attempts 2
   • Requires special handling of biopsy specimens

Medication Interference with Testing

Must Be Discontinued Before Testing

• Proton Pump Inhibitors (PPIs): Stop for at least 7 days
• Antibiotics and Bismuth compounds: Stop for at least 4 weeks
• H2-receptor antagonists: Stop for at least 24 hours 1

Medications That Do Not Interfere

• Ondansetron (Zofran)
• Fish oil supplements 1

Post-Treatment Testing

• Wait at least 4 weeks after completion of treatment before testing for eradication 2, 1
• Use UBT or SAT to confirm eradication, not serology 1

Common Pitfalls to Avoid

1. Inadequate medication washout period

   • PPIs can cause false-negative results if not discontinued for sufficient time

2. Testing too soon after treatment

   • Must wait at least 4 weeks after completion of therapy

3. Improper test selection

   • Serology should not be used to confirm eradication

4. Incorrect sample collection

   • For SAT, ensure proper stool sample size and handling

Test Selection Algorithm

1. For initial diagnosis in primary care:

   • Choose UBT or SAT based on local availability and patient preference 1
   • Consider "test and treat" strategy for patients under 45 years without alarm symptoms 2

2. For post-treatment confirmation:

   • UBT or SAT at least 4 weeks after treatment completion 2, 1

3. For patients with complicated peptic ulcer, gastric ulcer, or MALT lymphoma:

   • Endoscopy-based testing with biopsies from antrum and body 2

4. After two failed treatment attempts:

   • Consider culture and antibiotic susceptibility testing 2

By following these preparation guidelines, clinicians can maximize the accuracy of H. pylori testing and improve patient outcomes by ensuring appropriate diagnosis and treatment verification.