Rapid urease test, also known as the CLO test (Campylobacter-like organism test), is a

rapid diagnostic test A rapid diagnostic test (RDT) is a medical diagnostic test that is quick and easy to perform. RDTs are suitable for preliminary or emergency medical screening and for use in medical facilities with limited resources. They also allow point-of-care ...

for diagnosis of ''

Helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...

''. The basis of the test is the ability of ''H. pylori'' to secrete the

urease 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-contai ...

enzyme, which catalyzes the conversion of

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

and

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

Process

The test is performed at the time of

gastroscopy Esophagogastroduodenoscopy (EGD) or oesophagogastroduodenoscopy (OGD), also called by various other names, is a diagnostic endoscopic procedure that visualizes the upper part of the gastrointestinal tract down to the duodenum. It is considered ...

. A

biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a dise ...

of mucosa is taken from the

antrum ''This is a disambiguation page for the biological term. For the 2018 horror movie, see Antrum (film)'' In biology, antrum is a general term for a cavity or chamber, which may have specific meaning in reference to certain organs or sites in the bod ...

of the

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

, and is placed into a medium containing urea and an indicator such as

phenol red Phenol red (also known as phenolsulfonphthalein or PSP) is a pH indicator frequently used in cell biology laboratories. Chemical structure and properties Phenol red exists as a red crystal that is stable in air. Its solubility is 0.77 grams per ...

. 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.

Selective urease test

Selective urease tests differ from the single-layer rapid urease tests by their design and higher sensitivity and specificity. 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. 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. 106 0A AMA RUT EXPERT 80

Limitations

There is evidence to suggest that ''

H. pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...

'' moves proximal in the stomach in patients on therapy with

proton pump inhibitors Proton-pump inhibitors (PPIs) are a class of medications that cause a profound and prolonged reduction of stomach acid production. They do so by irreversibly inhibiting the stomach's H+/K+ ATPase proton pump. They are the most potent inhibitor ...

, and, as such, samples from the fundus and

body Body may refer to: In science * Physical body, an object in physics that represents a large amount, has mass or takes up space * Body (biology), the physical material of an organism * Body plan, the physical features shared by a group of anima ...

should be taken in these patients. Active gastrointestinal bleeding reduces accuracy of the test. The specificity and sensitivity of this test is high compared with

urea breath test 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 con ...

. 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 Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in ...

testing.

References

{{Clinical microbiology techniques Medical tests Digestive system procedures Helicobacter pylori