why choose 13C urea breath instead of 14C urea breath for H.pylori test?
Urea can be labelled with two different carbon isotopes:14C and 13C. The main difference between them is that the former is radioactive, whereas the latter is stable. The advantages of using 14C-urea are that it is cheap, so rapid that administering 14C-urea in a gelatin capsule allows an accurate response to be obtained from a single 10 minute breath sample, and does not require any test meal. However, although the dose of 14C has become progressively smaller and the test can now be performed with 1 μCi,which is equal to the natural background radiation received in one day, the main problems are still the availability of a nuclear medicine department or centres licensed for storage and disposal of radioactive substrates, shipping difficulties, and the copious amounts of labelled tracer needed to perform large scale epidemiological studies. The use of this unstable tracer can be recommended when the number of UBTs per annum in a given gastroenterological centre is less than 2500 and 14C facilities are available on site.
In contrast, 13C is a non-radioactive isotope that can be used safely for repeated testing, which is frequently required in clinical practice, and for detecting H pylori infection in children and women of childbearing age. Furthermore, 13C-urea has been the most widely used substrate in methodological studies performed to validate this kind of diagnostic test. Another relevant advantage of using the stable isotope is that breath samples can be sent by post or courier to remote analysis centres, thus promoting the distribution of the test, which can even be performed at home if the patients are adequately selected and instructed. The major drawbacks of13C-urea are the higher cost compared with14C-urea, and the need for expensive mass spectrometry, which is the most preferable device for measuring 13C enrichment in breath samples of subjects infected withH pylori.
This review focuses on the most recent advances in the machines used to measure the 13C isotope and on the most important aspects regarding the main UBT variable.