Editing Urea breath test (section)

==Principles and mechanism==
Patients swallow [[urea]] labelled with an uncommon [[isotope]], either [[radioactivity|radioactive]] [[carbon-14]] (nowadays preferred in many countries) 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 [[metabolism|metabolize]] urea to produce [[ammonia]]) 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 (physics)|scintillation]], whereas carbon-13 can be detected by [[isotope ratio mass spectrometry]] or simpler by [[Nondispersive infrared sensor|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.<ref>{{cite journal |last1=Haisch |first1=M. |last2=Hering |first2=P. |last3=Fuss |first3=W. |last4=Fabinski |first4=W. |date=July 1994 |title=A Sensitive Isotope Selective Nondispersive Infrared Spectrometer for 13 CO 2 and 12 CO 2 Concentration Measurements in Breath Samples |url=https://www.tandfonline.com/doi/full/10.1080/00211919408046740 |journal=Isotopenpraxis Isotopes in Environmental and Health Studies |language=en |volume=30 |issue=2–3 |pages=247–251 |doi=10.1080/00211919408046740 |issn=0021-1915}}</ref><ref>{{cite journal|doi= 10.1046/j.1365-2036.2001.00926.x|author= Shirin, H|last2= Kenet|first2= G|last3= Shevah|first3= O|last4= Wardi|first4= Y|last5= Birkenfeld|first5= S|last6= Shahmurov|first6= M|last7= Bruck|first7= R|last8= Niv|first8= Y|last9= Moss|first9= SF|last10= Avni|first10= Y.|title= Evaluation of a novel continuous real time 13C urea breath analyzer for Helicobacter pylori |journal= Aliment. Pharmacol. Ther. |volume=15|issue= 3|pages=389–394|year=2001|pmid=11207514|s2cid= 25680497|display-authors= 8|doi-access= }}</ref><ref>{{cite journal|doi= 10.1097/00004836-200308000-00009|author= Israeli, E|last2= Ilan|first2= Y|last3= Meir|first3= SB|last4= Buenavida|first4= C|last5= Goldin|first5= E|title= A novel 13C-urea breath test device for the diagnosis of Helicobacter pylori infection: continuous online measurements allow for faster test results with high accuracy |journal= J Clin Gastroenterol |volume=37|issue= 2|pages=139–41|year=2003|pmid=12869884  |s2cid= 13527961}}</ref>

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 (tests)|sensitivity]] and [[Specificity (tests)|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.<ref>{{cite journal|last1=Manaf|first1=Mohd Rizal Abdul|last2=Hassan|first2=Mohd Rohaizat|last3=Shah|first3=Shamsul Azhar|last4=Johani|first4=Fadzrul Hafiz|last5=Rahim|first5=Muhammad Aklil Abd|date=2019-07-24|title=13C-Urea Breath Test Accuracy for Helicobacter pylori Infection in the Asian Population: A Meta-Analysis|journal=Annals of Global Health|language=en|volume=85|issue=1|pages=110|doi=10.5334/aogh.2570|pmid=31348624|pmc=6659579|issn=2214-9996 |doi-access=free }}</ref>

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.<ref>{{cite journal|vauthors=Peng NJ, Lai KH, Liu RS, Lee SC, Tsay DG, Lo CC, Tseng HH, Huang WK, Lo GH, Hsu PI |title= Clinical significance of oral urease in diagnosis of Helicobacter pylori infection by [13C]urea breath test |journal= Dig Dis Sci |volume=46|issue= 8|pages=1772–8|year=2001|pmid= 11508681|doi= 10.1023/A:1010626225949 |s2cid= 225771 }}</ref>

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.<ref name=":0" /><ref name=":1" />