| Rapid urease test | |
|---|---|
 Rapid urease test | |
| Purpose | test for diagnosis of Helicobacter pylori. |
Rapid urease test, also known as the CLO test (Campylobacter-like organism test), is a rapid diagnostic test for diagnosis of Helicobacter pylori . [1] The basis of the test is the ability of H. pylori to secrete the urease enzyme, which catalyzes the conversion of urea to ammonia and carbon dioxide.
The test is performed at the time of gastroscopy. A biopsy of mucosa is taken from the antrum of the stomach, and is placed into a medium containing urea and an indicator such as phenol red. The urease produced by H. pylori hydrolyzes urea to ammonia, which raises the pH of the medium, and changes the color of the specimen from yellow (NEGATIVE) to red (POSITIVE).
Among different kinds of rapid urease tests (liquid-based, gel-based, dry cool) there is a design type with single-layer sensitive element — a layer impregnated simultaneously with urea and an indicator composition. Such a design bears the risk of false-positive result due to the pH value of the gastric biopsy when it is placed on the sensitive element. Excessive salivation and alkaline bile reflux into the stomach can shift the pH value of the biopsy of the stomach towards alkaline. Drugs that reduce the acidity of the stomach, also contribute to false positive results resulting from the alkalization. In each of these cases, the pH of the biopsy will be shifted to the alkaline side. All of these factors may trigger a non-targeted coloration of the sensitive element in a single-layer rapid urease test. The indicator would change color not in the course of the enzymatic reaction, which then causes alkalization of the medium as a result of ammonia formation, but under the effect of the pH of the gastric biopsy. [2]
Selective urease tests differ from the single-layer rapid urease tests by their design and higher sensitivity and specificity. [3] In contrast to single-layer rapid urease tests, selective urease tests have several layers, enabling separate enzymatic and indicator reactions. The sample is placed on the first layer impregnated with urea. Ammonia formed during the hydrolysis of urea by urease penetrates through a special selective membrane to the layer impregnated with the indicator composition. [4] Accordingly, the color change occurs directly during the enzymatic reaction. This avoids the influence of the pH value of the sample (gastric biopsy) on the result of a selective urease test, which virtually eliminates the occurrence of false-positive results. If the pH value of the sample is shifted to the acidic side, for example, in the case of increased acidity of gastric juice, this also does not distort the result of the selective urease test. [5]
There is evidence to suggest that H. pylori moves proximal in the stomach in patients on therapy with proton pump inhibitors [ citation needed ], and, as such, samples from the fundus and body should be taken in these patients.
Active gastrointestinal bleeding reduces accuracy of the test. [6]
The specificity and sensitivity of this test is high compared with urea breath test [ citation needed ]. The test is often done as part of point-of-care diagnostics, to eliminate the time and expense required to detect H. pylori on pathology testing.
The urea breath test is a rapid diagnostic procedure used to identify infections by Helicobacter pylori, a spiral bacterium implicated in gastritis, gastric ulcer, and peptic ulcer disease. It is based upon the ability of H. pylori to convert urea to ammonia and carbon dioxide. Urea breath tests are recommended in leading society guidelines as a preferred non-invasive choice for detecting H. pylori before and after treatment.
Peptic ulcer disease is a break in the inner lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of the intestines is a duodenal ulcer. The most common symptoms of a duodenal ulcer are waking at night with upper abdominal pain, and upper abdominal pain that improves with eating. With a gastric ulcer, the pain may worsen with eating. The pain is often described as a burning or dull ache. Other symptoms include belching, vomiting, weight loss, or poor appetite. About a third of older people with peptic ulcers have no symptoms. Complications may include bleeding, perforation, and blockage of the stomach. Bleeding occurs in as many as 15% of cases.
Ureases, functionally, belong to the superfamily of amidohydrolases and phosphotriesterases. Ureases are found in numerous bacteria, fungi, algae, plants, and some invertebrates, as well as in soils, as a soil enzyme. They are nickel-containing metalloenzymes of high molecular weight.
Helicobacter pylori, previously known as Campylobacter pylori, is a gram-negative, flagellated, helical bacterium. Mutants can have a rod or curved rod shape, and these are less effective. Its helical body is thought to have evolved in order to penetrate the mucous lining of the stomach, helped by its flagella, and thereby establish infection. The bacterium was first identified as the causal agent of gastric ulcers in 1983 by the Australian doctors Barry Marshall and Robin Warren.
Stomach cancer, also known as gastric cancer, is a cancer that develops from the lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a number of subtypes, including gastric adenocarcinomas. Lymphomas and mesenchymal tumors may also develop in the stomach. Early symptoms may include heartburn, upper abdominal pain, nausea, and loss of appetite. Later signs and symptoms may include weight loss, yellowing of the skin and whites of the eyes, vomiting, difficulty swallowing, and blood in the stool, among others. The cancer may spread from the stomach to other parts of the body, particularly the liver, lungs, bones, lining of the abdomen, and lymph nodes.
Delta cells are somatostatin-producing cells. They can be found in the stomach, intestine and the pancreatic islets. Delta cells comprise ca 5% of the cells in the islets but may interact with many more islet cells than suggested by their low numbers. In rodents, delta-cells are located in the periphery of the islets; in humans the islet architecture is generally less organized and delta-cells are frequently observed inside the islets as well. In both species, the peptide hormone Urocortin III (Ucn3) is a major local signal that is released from beta cells to induce the local secretion of somatostatin. It has also been suggested that somatostatin may be implicated in insulin-induced hypoglycaemia through a mechanism involving SGLT-2 receptors. Ghrelin can also strongly stimulate somatostatin secretion, thus indirectly inhibiting insulin release. Viewed under an electron microscope, delta-cells can be identified as cells with smaller and slightly more compact granules than beta cells.
Barry James Marshall is an Australian physician, Nobel Prize Laureate in Physiology or Medicine, Professor of Clinical Microbiology and Co-Director of the Marshall Centre at the University of Western Australia. Marshall and Robin Warren showed that the bacterium Helicobacter pylori plays a major role in causing many peptic ulcers, challenging decades of medical doctrine holding that ulcers were caused primarily by stress, spicy foods, and too much acid. This discovery has allowed for a breakthrough in understanding a causative link between Helicobacter pylori infection and stomach cancer.
Proteus vulgaris is a rod-shaped, nitrate-reducing, indole-positive and catalase-positive, hydrogen sulfide-producing, Gram-negative bacterium that inhabits the intestinal tracts of humans and animals. It can be found in soil, water, and fecal matter. It is grouped with the Morganellaceae and is an opportunistic pathogen of humans. It is known to cause wound infections and other species of its genera are known to cause urinary tract infections.
Alkaline mucus is a thick fluid produced by animals which confers tissue protection in an acidic environment, such as in the stomach.
Gastritis is inflammation of the lining of the stomach. It may occur as a short episode or may be of a long duration. There may be no symptoms but, when symptoms are present, the most common is upper abdominal pain. Other possible symptoms include nausea and vomiting, bloating, loss of appetite and heartburn. Complications may include stomach bleeding, stomach ulcers, and stomach tumors. When due to autoimmune problems, low red blood cells due to not enough vitamin B12 may occur, a condition known as pernicious anemia.
Achlorhydria and hypochlorhydria refer to states where the production of hydrochloric acid in gastric secretions of the stomach and other digestive organs is absent or low, respectively. It is associated with various other medical problems.
John Robin Warren is an Australian pathologist, Nobel Laureate and researcher who is credited with the 1979 re-discovery of the bacterium Helicobacter pylori, together with Barry Marshall. The duo proved to the medical community that the bacterium Helicobacter pylori is the cause of most peptic ulcers.
MALT lymphoma is a form of lymphoma involving the mucosa-associated lymphoid tissue (MALT), frequently of the stomach, but virtually any mucosal site can be affected. It is a cancer originating from B cells in the marginal zone of the MALT, and is also called extranodal marginal zone B cell lymphoma.
In medicine, the urea-to-creatinine ratio (UCR), known in the United States as BUN-to-creatinine ratio, is the ratio of the blood levels of urea (BUN) (mmol/L) and creatinine (Cr) (μmol/L). BUN only reflects the nitrogen content of urea and urea measurement reflects the whole of the molecule, urea is just over twice BUN. In the United States, both quantities are given in mg/dL The ratio may be used to determine the cause of acute kidney injury or dehydration.
This is a timeline of the events relating to the discovery that peptic ulcer disease and some cancers are caused by H. pylori. In 2005, Barry Marshall and Robin Warren were awarded the Nobel Prize in Physiology or Medicine for their discovery that peptic ulcer disease (PUD) was primarily caused by Helicobacter pylori, a bacterium with affinity for acidic environments, such as the stomach. As a result, PUD that is associated with H. pylori is currently treated with antibiotics used to eradicate the infection. For decades prior to their discovery, it was widely believed that PUD was caused by excess acid in the stomach. During this time, acid control was the primary method of treatment for PUD, to only partial success. Among other effects, it is now known that acid suppression alters the stomach milieu to make it less amenable to H. pylori infection.
Stomach diseases include gastritis, gastroparesis, Crohn's disease and various cancers.
The proton-gated urea channel is an inner-membrane protein essential for the survival to Helicobacter pylori. It enables the rapid influx of urea into the bacterium. It is closed at pH 7.0 and fully open at pH 5.0. Urease activity buffers the periplasm to pH 6.1. Using multiwavelength anomalous dispersion (MAD), its structure, a compact hexameric ring about 95 Å in diameter and 45 A ̊ in height, was determined. The centre is filled with a lipid plug that forms an asymmetric bilayer. Amino residues that can be protonated in the periplasmic domain are important for proton sensing or gating.
Helicobacter felis is a bacterial species in the Helicobacteraceae family, Campylobacterales order, Helicobacter genus. This bacterium is Gram-negative, microaerophilic, urease-positive, and spiral-shaped. Its type strain is CS1T. It can be pathogenic.
Diagnostic microbiology is the study of microbial identification. Since the discovery of the germ theory of disease, scientists have been finding ways to harvest specific organisms. Using methods such as differential media or genome sequencing, physicians and scientists can observe novel functions in organisms for more effective and accurate diagnosis of organisms. Methods used in diagnostic microbiology are often used to take advantage of a particular difference in organisms and attain information about what species it can be identified as, which is often through a reference of previous studies. New studies provide information that others can reference so that scientists can attain a basic understanding of the organism they are examining.
Helicobacter cetorum is a Gram-negative, microaerophilic, spiral (helical) bacterium that is usually found in the stomachs of whales and dolphins. Based on 16S rRNA sequencing, its genome is very similar to that of Helicobacter pylori in that it can cause gastric disease in these animals. Originally isolated among Atlantic white-sided dolphins and Beluga whales in 2000, H. cetorum has been associated with hemorrhages throughout its entire gastrointestinal tract, but its role has not yet been discovered. Prior to the discovery of H. cetorum, there have not been any other Helicobacter species reported in dolphins.