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Microbiology

H. pylori Detection

Helicobacter pylori is a significant cause of chronic gastritis, peptic ulcers, and gastric cancer. Accurate and reliable detection methods are crucial for diagnosis, treatment, and eradication monitoring

General Principles

  • Gastric Colonization: H. pylori colonizes the gastric mucosa, causing inflammation and damage
  • Diagnostic Goals: To detect the presence of H. pylori and/or its effects on the stomach
  • Methods
    • Invasive Tests: Require endoscopy and biopsy
    • Non-invasive Tests: Do not require endoscopy
  • Treatment and Monitoring: The identification of H. pylori is used to guide treatment and to monitor the effectiveness of eradication therapy

Detection Methods

Invasive Tests (Endoscopy Required)

  • Gastric Biopsy
    • Procedure: Endoscopy is performed, and biopsies are taken from the gastric mucosa
    • Histology: Examination of the biopsy tissue under a microscope
      • Staining: Hematoxylin and eosin (H&E) stain to visualize the inflammatory changes
      • Special Stains: Stains (e.g., Giemsa, Warthin-Starry) to visualize H. pylori
    • Advantages: Direct visualization of H. pylori and the degree of inflammation
    • Disadvantages: Invasive, requires expertise
  • Rapid Urease Test (CLO Test)
    • Principle: H. pylori produces urease, which breaks down urea into ammonia and carbon dioxide
    • Procedure: A gastric biopsy specimen is placed in a test well containing urea and a pH indicator
    • Result: A color change (usually yellow to red) indicates the production of ammonia and a positive test
    • Advantages: Rapid, inexpensive, easy to perform
    • Disadvantages: False negatives are possible
  • Culture
    • Procedure: A gastric biopsy specimen is cultured on selective media (e.g., Skirrow’s medium)
    • Incubation: Incubate microaerophilically (low oxygen, high CO2) for several days
    • Identification: Identify H. pylori based on its characteristic morphology and biochemical tests
    • Advantages: Allows for antibiotic susceptibility testing
    • Disadvantages: Can be slow and technically demanding

Non-Invasive Tests (No Endoscopy Required)

  • Urea Breath Test (UBT)
    • Principle: Based on the urease activity of H. pylori
    • Procedure: The patient drinks a solution containing urea labeled with a carbon isotope (e.g., 13C or 14C). If H. pylori is present, the urea is broken down to labeled carbon dioxide, which is exhaled and detected in the breath
    • Advantages: Non-invasive, accurate, relatively inexpensive
    • Disadvantages: False negatives are possible
  • Fecal Antigen Test (FAT)
    • Principle: Detects H. pylori antigens in stool
    • Procedure: Stool sample is tested using an immunoassay (e.g., EIA)
    • Advantages: Non-invasive
    • Disadvantages: The sensitivity can vary
  • Serology (Antibody Detection)
    • Principle: Detects antibodies to H. pylori in the blood
    • Procedure: A blood sample is tested using an immunoassay (e.g., ELISA)
    • Advantages: Non-invasive
    • Disadvantages: Cannot distinguish between past and present infection. The antibodies can persist for months

Test Selection and Interpretation

  • Choice of Test: The selection of the test depends on:
    • Clinical Presentation
    • Availability of Resources
    • Patient Factors
  • Diagnostic Algorithm
    • Initial Diagnosis: UBT or FAT are often used
    • Endoscopy: If UBT/FAT is inconclusive or if there are signs of complications (e.g., ulcers, bleeding)
    • Eradication Monitoring: UBT, FAT, or biopsy with culture are often used to confirm eradication
  • Interpretation
    • Positive Test: Indicates the presence of H. pylori
    • Negative Test: Indicates that H. pylori is not present
    • False Positives/Negatives: Possible with any test. This can be related to:
      • Antibiotic Use: May cause a false negative
      • PPI Use: May cause a false negative
      • Bleeding: May cause a false negative

Additional Considerations

  • Patient Preparation: Some tests require the patient to stop taking medications
  • Test Performance: Proper technique is critical
  • Eradication Therapy: Treatment of H. pylori infection typically involves a combination of antibiotics and acid-suppressing medications
  • Follow-Up Testing: To confirm eradication after treatment

Key Terms

  • Helicobacter pylori (H. pylori): A bacterium that colonizes the gastric mucosa
  • Gastritis: Inflammation of the stomach lining
  • Peptic Ulcer: A sore in the lining of the stomach or duodenum
  • Gastric Cancer: Cancer of the stomach
  • Endoscopy: A procedure to visualize the inside of the digestive tract
  • Biopsy: The removal of a tissue sample for examination
  • Urease: An enzyme produced by H. pylori that breaks down urea
  • Urea Breath Test (UBT): A non-invasive test
  • Fecal Antigen Test (FAT): A non-invasive test
  • Serology: Testing for antibodies in the blood
  • Immunoassay: A laboratory test that uses antibodies to detect a substance
  • Microaerophilic: Requiring low oxygen and high CO2
  • Eradication Therapy: Treatment to eliminate H. pylori infection
  • PPI: Proton Pump Inhibitor. A medication that reduces stomach acid
  • ELISA: Enzyme-linked immunosorbent assay. A serology test