Urea breath test
Encyclopedia
The urea breath test is a rapid diagnostic
procedure used to identify infection
s 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.
labelled with an uncommon isotope
, either radioactive carbon-14
or non-radioactive carbon-13
. In the subsequent 10–30 minutes, the detection of isotope-labelled carbon dioxide
in exhaled breath indicates that the urea was split; this indicates that urease
(the enzyme
that H. pylori uses to metabolize
urea) is present in the stomach
, and hence that H. pylori bacteria are present.
For the two different forms of urea, different instrumentation is required; carbon-14 is normally measured by scintillation
. Carbon-13 can be detected by a breath test using carbon-13 by isotope ratio mass spectrometry or by mass correlation spectrometry. For carbon-13, a baseline breath sample before taking urea is required for comparison with the post-urea sample. In case breath sample analysis is done using isotope ratio mass spectrometry, a 2-point sampling is required with a 20 to 30-minute duration between them. Samples are sent to a reference laboratory for analysis. Mass correlation spectrometry can be performed as an office-based test since breath samples are continuously collected, and results are provided immediately within minutes.
The difference between the pre and post urea measurements is used to determine infection. This value is compared to a cut-off value. Results below the value are assumed to be negative, those above positive. The cut-off value itself is determined by comparing the results of patients with two or more different detection methods. The value is chosen that gives the best combination of sensitivity and specificity.
The test measures active H. pylori infection. If antibiotics are depressing the amount of H. pylori present, or the stomach conditions are less acidic than normal, the amount of urease present will be lessened.
Accordingly the test should only be performed 14 days after stopping acid reducing medication (proton pump inhibitor
s, PPI) or 28 days after stopping antibiotic treatment. Some clinicians believe that a reservoir of H. pylori in dental plaque can affect the result.
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...
procedure used to identify infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
s by Helicobacter pylori
Helicobacter pylori
Helicobacter pylori , previously named Campylobacter pyloridis, is a Gram-negative, microaerophilic bacterium found in the stomach. It was identified in 1982 by Barry Marshall and Robin Warren, who found that it was present in patients with chronic gastritis and gastric ulcers, conditions that were...
, a spiral bacterium implicated in gastritis
Gastritis
Gastritis is an inflammation of the lining of the stomach, and has many possible causes. The main acute causes are excessive alcohol consumption or prolonged use of nonsteroidal anti-inflammatory drugs such as aspirin or ibuprofen. Sometimes gastritis develops after major surgery, traumatic...
, gastric ulcer, and peptic ulcer
Peptic ulcer
A peptic ulcer, also known as PUD or peptic ulcer disease, is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. It is defined as mucosal erosions equal to or greater than 0.5 cm...
disease. It is based upon the ability of H. pylori to convert urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
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.
Principles and mechanism
Patients swallow ureaUrea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
labelled with an uncommon isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
, either radioactive carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...
or non-radioactive carbon-13
Carbon-13
Carbon-13 is a natural, stable isotope of carbon and one of the environmental isotopes. It makes up about 1.1% of all natural carbon on Earth.- Detection by mass spectrometry :...
. In the subsequent 10–30 minutes, the detection of isotope-labelled carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
in exhaled breath indicates that the urea was split; this indicates that urease
Urease
Urease is an enzyme that catalyzes the hydrolysis of urea into carbon dioxide and ammonia. The reaction occurs as follows:In 1926, James Sumner showed that urease is a protein. Urease is found in bacteria, yeast, and several higher plants. The structure of urease was first solved by P.A...
(the enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that H. pylori uses to metabolize
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
urea) is present in the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, and hence that H. pylori bacteria are present.
For the two different forms of urea, different instrumentation is required; carbon-14 is normally measured by scintillation
Scintillation
Scintillation can refer to:*Scintillation , atmospheric effects which influence astronomical observations*Interplanetary scintillation, fluctuations of radio waves caused by the solar wind...
. Carbon-13 can be detected by a breath test using carbon-13 by isotope ratio mass spectrometry or by mass correlation spectrometry. For carbon-13, a baseline breath sample before taking urea is required for comparison with the post-urea sample. In case breath sample analysis is done using isotope ratio mass spectrometry, a 2-point sampling is required with a 20 to 30-minute duration between them. Samples are sent to a reference laboratory for analysis. Mass correlation spectrometry can be performed as an office-based test since breath samples are continuously collected, and results are provided immediately within minutes.
The difference between the pre and post urea measurements is used to determine infection. This value is compared to a cut-off value. Results below the value are assumed to be negative, those above positive. The cut-off value itself is determined by comparing the results of patients with two or more different detection methods. The value is chosen that gives the best combination of sensitivity and specificity.
The test measures active H. pylori infection. If antibiotics are depressing the amount of H. pylori present, or the stomach conditions are less acidic than normal, the amount of urease present will be lessened.
Accordingly the test should only be performed 14 days after stopping acid reducing medication (proton pump inhibitor
Proton pump inhibitor
Proton-pump inhibitors are a group of drugs whose main action is a pronounced and long-lasting reduction of gastric acid production. They are the most potent inhibitors of acid secretion available today. The group followed and has largely superseded another group of pharmaceuticals with similar...
s, PPI) or 28 days after stopping antibiotic treatment. Some clinicians believe that a reservoir of H. pylori in dental plaque can affect the result.
See also
- Rapid urease testRapid urease testRapid urease test, also known as the CLO test , is a rapid test for diagnosis of Helicobacter pylori. 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 bicarbonate.-Process:The test is performed at the time of...
(done on biopsyBiopsyA biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...
specimens after upper endoscopy) - Breath testBreath testA breath test is a type of test performed on air generated from the act of exhalation.Types include:*Breathalyzer - By far the most common usage of this term relates to the legal breath test to determine if a person is driving under the influence of alcohol.*Hydrogen breath test - it is becoming...