Helicobacter Pylori Tests
By Jeyashree Sundaram, MBA
H. pylori (Helicobacter pylori) is a bacterium found in the gastric mucosa of humans. H. pylori infections are common. The Centers for Disease Control and Prevention (CDC) has estimated that about two-thirds of the population in the world is infected by H. pylori.
Compared with developed nations, the infection rates in developing countries are much higher. Although H. pylori infection does not create illness in most instances, it is considered to be a primary risk factor for the majority of stomach ulcers, such as peptic ulcers, as well as for diseases in the upper small intestine, and gastric cancer.
Tests for detecting H. pylori are of three types: (1) invasive tests, (2) less invasive tests, and (3) non-invasive tests.
Using endoscopy, biopsy specimens are obtained for evaluation. Various tests are carried out to detect the presence of bacteria in these specimens, and H. pylori is sought to be cultured from the specimen.
To overcome the acidity in the stomach, these bacteria secrete urease – an enzyme that produces ammonia by converting the chemical urea. The biopsy specimens are tested by a card test, which will change its color if urease is present in the specimen. Results can be obtained within a few minutes or sometimes even 24 hours.
H. pylori has a spiral shape which helps it to hide in the less acidic areas of the stomach. For instance, the bacteria may be attached to the cells lining the internal surface of the stomach. As the immune cells are not able to penetrate the lining of the stomach, they fail to eliminate the H. pylori. Due to technical limitations, some invasive tests may not yield accurate results. When the bacteria are hidden in this way, the biopsy may skip the hidden areas.
Advancements in techniques such as endocytoscopy, narrow band imaging, and confocal laser endomicroscopy may allow us to view the abnormalities of the gastric mucosa in a magnified view. In particular, using confocal laser endomicroscopy, H. pylori can be detected by imaging live tissue during endoscopy. Endoscopists are often able to see single bacteria and bacterial clusters present on the surface and hidden in inner portions using contrast stains such as intravenous fluorescein and topical acriflavine in endomicroscope. This advancement is considered to be a breakthrough in the present diagnostic possibilities.
Less Invasive Tests
In less invasive techniques such as the Entero-Test (string test), the patient ingests a capsule that is attached to an absorbent string and the capsule dissolves in the lumen of the stomach. The gastric juice is collected on the string. The physician takes samples from the string which are used for testing and culturing H. pylori.
Gastric juice can also be obtained with the help of a nasogastric tube, and H. pylori infection can be detected from it, instead of using the more invasive endoscopy method.
In the extendable oro-gastric brush method, the patient is asked to swallow the brush assembly of diameter 5 mm. The brush is extended into the stomach and it is used to brush the mucosa 3-4 times. It is then withdrawn into the protective sleeve and removed.
Stains such as gram stain, fluorescent acridine orange stain, rapid Giemsa, Warthin Starry, Cresyl violet, Ziehl-Nielsen, Genta, Gimenez, and H. pylori silver stain are used to visualize various inflammatory cells, with a sensitivity of about 80%, and rapid results.
Blood testing is used to diagnose the infection by measuring the level of antibodies to H. pylori. Repeat tests can also be used to check whether the infection is eradicated, after several months.
Unlike blood tests where the antibody levels are measured and compared within a 6-month window, breath tests are done within 30 days post-treatment. Breath tests are best used to ensure that the bacteria have been eliminated.
Patients are advised to stop consuming bismuth-containing medicines (e.g., proton pump inhibitors, Pepto-Bismol) and antibiotics 2 weeks prior to the test. Patients are supplied with urea in the form of either radioactive or nonradioactive compound, to ingest. The urea is converted into carbon dioxide if H. pyroli is present, and this is detected in the exhaled breath. Performing radioactive urea (breath) tests is comparatively easy as the required equipment is readily available in X-ray units. When compared to taking a chest X-ray, exposure to radiation is less using this method.
It identifies evidence of H. pylori by testing for H. pylori antigens in stool, and is also used to confirm that the infection has been eradicated after the treatment.
H. pylori stool antigen test and urea breath test are best suited to diagnose infection among children. ones. It is safe to use non-radioactive urea tests for children.
Susceptibility testing methods are applied to detect H. pylori resistance to antibiotics. Phenotypic methods such as the agar dilution method, the breakpoint susceptibility testing, and Etest, as well as genotypic methods including the real-time polymerase chain reaction (PCR) and PCR-RFLP (Restriction Fragment Length Polymorphism) are also used for detecting H. pylori.
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Last Updated: Feb 26, 2019
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