I18 Gut 1999;45(Suppl I):I18–I22 The 13C urea breath test in the diagnosis of Helicobacter pylori infection Gut: first published as 10.1136/gut.45.2008.i18 on 1 July 1999. Downloaded from V Savarino, S Vigneri, G Celle Summary simplify and optimise it, including changes to The urea breath test (UBT) is one of the most the dose of urea used, sample timing, test meal, important non-invasive methods for detecting and cut oV values to distinguish infected from Helicobacter pylori infection. The test exploits uninfected subjects. Despite these modifica- the hydrolysis of orally administered urea by tions, the accuracy of the test has remained the enzyme urease, which H pylori produces in high and this is the best confirmation of its large quantities. Urea is hydrolysed to ammo- robustness. nia and carbon dioxide, which diVuses into the The test exploits the large amount of urease blood and is excreted by the lungs. Isotopically produced by H pylori, as this enzyme hydro- labelled CO2 can be detected in breath using lyses the orally administered, labelled urea into various methods. ammonia and labelled CO2, which is absorbed Labelling urea with 13C is becoming increas- through the mucus layer of the stomach and ingly popular because this non-radioactive iso- then transported to the lungs via the blood- tope is innocuous and can be safely used in stream for excretion. Isotope enrichment can children and women of childbearing age. be measured by various methods in breath Breath samples can also be sent by post or cou- samples collected at appropriate times. rier to remote analysis centres. The test is easy Urea can be labelled with two diVerent carbon to perform and can be repeated as often as isotopes: 14C and 13C. The main diVerence required in the same patient. A meal must be between them is that the former is radioactive, given to increase the contact time between the whereas the latter is stable. The advantages of tracer and the H pylori urease inside the stom- using 14C-urea are that it is cheap, so rapid that ach. The test has been simplified to the point administering 14C-urea in a gelatin capsule that two breath samples collected before and allows an accurate response to be obtained from 30 minutes after the ingestion of urea in a liq- a single 10 minute breath sample,23 and does uid form suYce to provide reliable diagnostic not require any test meal. However, although the information. The cost of producing 13C-urea is dose of 14C has become progressively smaller high, but it may be possible to reduce the dos- and the test can now be performed with 1 µCi,3 http://gut.bmj.com/ age further by administering it in capsule form. which is equal to the natural background radia- An isotope ratio mass spectrometer (IRMS) tion received in one day,34 the main problems is generally used to measure 13C enrichment in are still the availability of a nuclear medicine breath samples, but this machine is expensive. department or centres licensed for storage and In order to reduce this cost, new and cheaper disposal of radioactive substrates, shipping diY- equipment based on non-dispersive, isotope culties, and the copious amounts of labelled selective, infrared spectroscopy (NDIRS) and tracer needed to perform large scale epidemio- on September 23, 2021 by guest. Protected copyright. laser assisted ratio analysis (LARA) have logical studies. The use of this unstable tracer recently been developed. These are valid alter- can be recommended when the number of natives to IRMS although they cannot process UBTs per annum in a given gastroenterological the same large number of breath samples centre is less than 2500 and 14C facilities are simultaneously. available on site.5 These promising advances will certainly In contrast, 13C is a non-radioactive isotope Dipartimento di 13 Medicina Interna e promote the wider use of the C-UBT, which is that can be used safely for repeated testing, Specialità Mediche, especially useful for epidemiological studies in which is frequently required in clinical practice, Cattedra di children and adults, for screening patients and for detecting H pylori infection in children Gastroenterologia, before endoscopy, and for assessing the efficacy and women of childbearing age. Furthermore, Università di Genova, of eradication regimens. 13C-urea has been the most widely used Italy V Savarino substrate in methodological studies performed G Celle Introduction to validate this kind of diagnostic test. Another Many diagnostic methods have been developed relevant advantage of using the stable isotope is Istituto di Medicina over the past 15 years to detect Helicobacter that breath samples can be sent by post or cou- Interna e Geriatria, pylori infection—some invasive (rapid urease rier to remote analysis centres, thus promoting Università di Palermo, test, histology, culture, and polymerase chain the distribution of the test, which can even be Italy S Vigneri reaction) because they cannot be performed performed at home if the patients are adequately without endoscopy, and others non-invasive selected and instructed.6 The major drawbacks Correspondence to: (serology, urea breath test (UBT) and, more of 13C-urea are the higher cost compared with Professor V Savarino, recently, H pylori antigen determination on Dipartimento di Medicina Interna e Specialità faeces). Of the latter, the UBT is being increas- Abbreviations used in this paper: UBT, urea breath Mediche, Cattedra di ingly used both in pretreatment and post- Gastroenterologia, Università test; IRMS, isotope ratio mass spectrometer; NDIRS, treatment phases. non-dispersive, isotope selective, infrared spectroscopy; di Genova, Viale Benedetto 1 XV, n. 6, 16132 Genova, Since it was first described by Graham et al, LARA, laser assisted ratio analysis; PPI, proton pump Italy. the test has been modified extensively to inhibitor; ROC, receiver operator characteristic. Urea breath test in the diagnosis of H pylori infection I19 13 12 Table 1 Comparison of the main characteristics of three diVerent types of equipment for measuring the CO2 to CO2 ratio in breath samples Characteristics of Mass spectrometer Infrared spectrometer Laser assisted ratio Gut: first published as 10.1136/gut.45.2008.i18 on 1 July 1999. Downloaded from the instruments (IRMS) (NDIRS) analyser (LARA) Weight 90 kg 12 kg 350 kg Reference gas Necessary Enclosed Necessary Carrier gas Helium supply None None Analysis time 120 seconds 90 seconds 60 seconds Automation For 220 samples For 16 samples For 60 samples Breath sample 10 ml glass tube 1200 breath bag 12 ml plastic tube Sample mailing Favourable Not practicable Favourable Multitasking software Commonly available Unnecessary Planned Technical expertise Easy to operate Easy to operate Easy to operate After sales support Often required Low maintenance Low maintenance Reported reliability 90–100% 90–98% Limited experience Approximate price 75 000 Euros 40 000 Euros 60 000 Euros 14C-urea, and the need for expensive mass spec- time. NDIRS does not require helium as the trometry, which is the most preferable device for carrier gas and has the lowest weight and price, measuring 13C enrichment in breath samples of but it can analyse only a small number of sam- subjects infected with H pylori. ples and so does not need multitasking This review focuses on the most recent software. The LARA system has the quickest advances in the machines used to measure the analysis time; the other characteristics are aver- 13C isotope and on the most important aspects age compared with the other two machines, regarding the main UBT variables. especially with regard to the number of samples it can process and the cost. Integrated bar code Measuring equipment readers and the use of multitasking programs 13 13 12 have made running IRMS instruments much C is measured as the CO2: CO2 isotope ratio and is expressed as delta over baseline easier; however, they do require more mainte- (DOB) per mil (‰) with respect to the nance than NDIRS and LARA systems. IRMS international reference standard represented and LARA are more suitable for gastroentero- by the Pee Dee Belemnite limestone. The logical centres requiring large quantity, auto- diVerence in isotope masses (45:44) is detected mated analysis, whereas NDIRS is more with extreme accuracy by the sector magnet suitable for small laboratories in which the contained in the mass spectrometer (IRMS). daily number of assays is not high. In this light, This equipment also requires a gas chromato- a small, new, cheap, infrared device for examination of only two breath samples has graph because CO2 has to be carefully purified from the whole breath prior to introduction been developed to be used exclusively in the into the mass spectrometer. The precision of doctor’s oYce.16 In the endless attempt to http://gut.bmj.com/ measurements made by conventional IRMS render the test cheaper and to increase the can be as high as 0.01‰7 and this allows very number of laboratories where it can be low isotopic enrichments to be detected. As 13C performed, other investigators have shown that 13 12 a gas chromatograph coupled with a mass is measured as the ratio of CO2 to CO2, there is no need for a large volume of expired air and selective detector, which is available in many a 10 ml sample is enough to obtain reliable analytical and biomedical settings, can also be 5 13 17 18 diagnostic information. Furthermore, the ex- reliably used for C-UBT. on September 23, 2021 by guest. Protected copyright. amination results do not depend on the body mass, so it is not necessary to take this variable Concomitant medication into account.8 The 13C-UBT is a simple and innocuous assay If a mass spectrometer is the most preferable which requires only few precautions in order to machine for detecting 13C excess in breath obtain accurate results.