Interpretation
Background
H. pylori is a micro-aerophilic, spirally-shaped, gram-negative bacterium with unipolar flagella, requiring carbon dioxide and a rich growth media. It lives on the human gastric mucosa, and colonization stops abruptly where gastric mucosa ends. H . pylori causes chronic gastritis, duodenal and stomach ulcers, and is associated with an increased risk of gastric cancer. Transmission is by ingestion, such as via the faecal-oral route. Once colonization in the stomach is established, H. pylori will usually persist indefinitely unless antimicrobial therapy is given. Its elimination allows healing of ulcers without recurrence.
H. pylori colonizes the stomach by the use of its flagella to burrow through the mucus to reach the stomach epithelial cell layer. In addition, urease, produced by H. pylori , is important for its survival in the harsh acidic environment in the stomach as urease is able to degrade urea into carbon dioxide and ammonia, which helps in neutralizing the gastric acid.
Diagnositic Interpretation
| Results |
Interpretation |
| Negative |
Indicates absence of H. pylori stool antigen, (or the antigen level is below that can be detected by the assay) |
| Equivocal |
For samples with equivocal results on initial testing, a new specimen should be collected |
| Positive |
Indicates the presence of detectable H. pylori stool antigen |
The faecal antigen test has been reported to have a sensitivty of 94-95%, specificity of 94-97%, and positive predictive value of 84%. Sensitivity and specificity of the test are comparable to carbon-13 urea breath testing for H. pylori diagnosis.
False-negative results can occur if the patient has used antimicrobials in the last 4 weeks, or used proton pump inhibitors/bismuth in the last 2 weeks prior to testing. Accuracy of the test can also be reduced if the patient had upper GI bleeding or if the faecal specimen is unformed or watery consistency.
Test Method
Principle: Sandwich chemiluminescent immunoassay
Assay: Diasorin
Analyser: Liaison XL
Uncertainty of Measurement
Faecal H. pylori antigen is currently reported qualitatively. In addition to analytical variation in the method itself, there is also variation due to stool sampling variability, and variation in antigen excretion from day to day. Further discussions can be directed to the on call Chemical Pathologist via LabPlus Lablink.