The urea breath test is a rapid
diagnostic
Diagnosis (: diagnoses) is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in a lot of different academic discipline, disciplines, with variations in the use of logic, analytics, and experience, to determine " ...
procedure used to identify
infection
An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...
s by ''
Helicobacter pylori
''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...
'', a spiral
bacterium
Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
implicated in
gastritis,
gastric ulcer, and
peptic ulcer
Peptic ulcer disease is when the inner part of the stomach's gastric mucosa (lining of the stomach), the first part of the small intestine, or sometimes the lower esophagus, gets damaged. An ulcer in the stomach is called a gastric ulcer, while ...
disease. It is based upon the ability of ''H. pylori'' to convert
urea
Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...
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
urea
Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...
labelled with an uncommon
isotope
Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
, either
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...
carbon-14
Carbon-14, C-14, C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...
(nowadays preferred in many countries) or non-radioactive
carbon-13
Carbon-13 (13C) is a natural, stable isotope of carbon with a nucleus containing six protons and seven neutrons. As one of the environmental isotopes, it makes up about 1.1% of all natural carbon on Earth.
Detection by mass spectrometry
A m ...
. In the subsequent 10–30 minutes, the detection of isotope-labelled
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
in exhaled breath indicates that the urea was split; this indicates that
urease
Ureases (), functionally, belong to the superfamily of amidohydrolases and phosphotriesterases. Ureases are found in numerous Bacteria, Archaea, fungi, algae, plants, and some invertebrates. Ureases are nickel-containing metalloenzymes of high ...
(the
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
that ''H. pylori'' uses to
metabolize urea to produce
ammonia
Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
) is present in the
stomach
The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
, 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, whereas carbon-13 can be detected by
isotope ratio mass spectrometry
Isotope-ratio mass spectrometry (IRMS) is a specialization of mass spectrometry, in which mass spectrometric methods are used to measure the relative abundance of isotopes in a given sample.
This technique has two different applications in the e ...
or simpler by
nondispersive infrared (NDIR) spectrometry. For each of these methods, a baseline breath sample is required before taking the isotope-labeled urea, for comparison with the post-urea sample, with a 15- to 30-minute duration between them. Samples may be sent to a reference laboratory for analysis. Alternatively, NDIR spectrometry can be performed by a table-top instrument as an office-based test, 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. Both carbon-14 and carbon-13 urea breath tests have high sensitivity and specificity, though the carbon-13 test is preferred in certain populations due to its non-radioactive nature.
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 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. The body eventually synthesizes ne ...
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.
The test is especially done accompanying an eradication therapy by antibiotics (to avoid overdosing) or to check the success of an ulcer operation. In both cases, immunological tests can give false positive results.
See also
*
Rapid urease test (done on at time of gastroscopy)
*
Breath test
References
External links
Typical testing procedure
{{DEFAULTSORT:Urea Breath Test
Breath tests
Digestive system procedures
Helicobacter pylori