Helicobacter pylori (H.pylori) is a gram negative, curved or spiral shaped bacteria. It is the major cause of peptic ulcer disease and gastritis. Approximately two-thirds of the world’s population are infected with H.pylori. H.pylori is found in the gastric mucous layer or adherent to the epithelial lining of the stomach and causes more than 90% of duodenal ulcers and up to 80% of gastric ulcers.
Persons with active gastric or duodenal ulcers or documented history of ulcers should be tested for H. pylori.
Various tests are available to diagnose H. pylori infection. These tests can be categorized into those that are based on direct assessment of gastric biopsies (endoscopic testing) and indirect tests (nonendoscopic testing) that detect an immunological response (i.e. antibodies against H. pylori) or metabolic products (i.e. urease activity) of H. pylori.
In order to optimize the diagnosis of H. pylori, it is usually recommended that several tests be used together. The choice of particular tests will depend on the locally available facilities, cost consideration and clinical circumstances in which the diagnosis of H. pylori is made.
The different tests for the detection of H. pylori are;
- Serology: Serological tests that measure specific pylori IgG antibodies can determine if a person has been infected. The sensitivity and specificity of these assays range from 80% to 95% depending upon the assay used. A positive serology indicates present or past infection. A positive antibody screen should be confirmed by a different tests such as fecal antigen, urea breath test or other invasive tests.
- Urea breath test: In this test, the patient is given either 13C- or 14C-labeled urea to ingest/drink (depending on the form; capsule or liquid). H. pylori metabolizes the urea rapidly, and the labeled carbon is absorbed into the blood and exhaled via the breath. This labeled carbon can then be measured as CO2 in the patient’s expired breath to determine whether H.pylori is present. The sensitivity and specificity of the breath test ranges from 94% to 98%.
- Fecal antigen test (FAT): H. pylori stool antigen is a reliable noninvasive tool to screen H. pylori infection. The fecal antigen test identifies H. pylori antigen in the stool by enzyme immunoassay with the use of polyclonal anti-H. pylori antibody.
Tests mentioned below require biopsy specimens of the stomach or duodenum. Test sample is taken during upper esophagogastroduodenal endoscopy.
- Microscopy: Histologic identification of organisms – considered the gold standard of diagnostic tests. Microscopy of gram-stained smears or imprint of gastric biopsies reveals curved gram-negative rods resembling Helicobacter.
- Culture: Culture of biopsy specimens for H. pylori requires sophisticated conditions. H. pylori can grow on different solid media containing blood or blood products (blood or lysed blood agar plates) but requires a microaerophilic (less oxygen tolerance) bacteria. Culture is necessary to isolate agents to perform antimicrobial susceptibility testing.
- Rapid Urease Testing (RUT): Rapid Urease testing identifies active H. pylori infection through the organism’s urease activity. Gastric biopsies are obtained and placed into an agar gel or on a reaction strip containing urea, a buffer, and a pH-sensitive indicator. In the presence of H. pylori’s urease, urea is metabolized to ammonia and bicarbonate leading to a pH increase in the micro-environment of
the organism. A change in color of the pH sensitive indicator signifies the presence of active infection. Commercially available kits yield results in 1–24 h.
- Molecular Tests: PCR is a DNA amplification technique that utilizes the rapid production of multiple copies of a target DNA sequence to identify H. pylori. This testing method is highly specific and may be more sensitive than other biopsy-based diagnostic techniques.
Advantages and disadvantages of diagnostic testing for Helicobacter pylori
|Histology||Excellent Sensitivity and specificity||Expensive and requires infrastructure and trained personnel|
|Rapid Urease Testing||Inexpensive and provides rapid results. Excellent specificity and very good sensitivity in properly selected patients.||Sensitivity significantly reduced in post- treatment setting|
|Culture||Excellent specificity. Allows determination of antibiotic sensitivities.||Expensive, difficult to perform, and not widely available.|
|Antibody testing (quantitative and qualitative)||Inexpensive, widely available, very good negative predictive value (NPV).||Positive predictive value (PPV) dependent upon background H. pylori prevalence. Not recommended after H.pylori therapy.|
|Urea breath tests
|Identifies active H.pylori infection. Excellent PPV and NPV regardless of H.pylori prevalence.|
|Fecal antigen test
|Identifies active H.pylori infection. Excellent positive and negative predictive values regardless of H.pylori prevalence. Useful before and after H.pylori therapy.||Polyclonal test less well validated than the UBT in the post-treatment setting. Monoclonal test appears reliable before and after antibiotic therapy. Unpleasantness associated with collecting stool.|