Cut-off point, timing and pitfalls of the 13C-urea breath test as measured by infrared spectrometry

Non-invasive diagnostic tests for Helicobacter pylori infection

BACKGROUND

Helicobacter pylori (H pylori) infection has been implicated in a number of malignancies and non-malignant conditions including peptic ulcers, non-ulcer dyspepsia, recurrent peptic ulcer bleeding, unexplained iron deficiency anaemia, idiopathic thrombocytopaenia purpura, and colorectal adenomas. The confirmatory diagnosis of H pylori is by endoscopic biopsy, followed by histopathological examination using haemotoxylin and eosin (H & E) stain or special stains such as Giemsa stain and Warthin-Starry stain. Special stains are more accurate than H & E stain. There is significant uncertainty about the diagnostic accuracy of non-invasive tests for diagnosis of H pylori.

OBJECTIVES

To compare the diagnostic accuracy of urea breath test, serology, and stool antigen test, used alone or in combination, for diagnosis of H pylori infection in symptomatic and asymptomatic people, so that eradication therapy for H pylori can be started.

SEARCH METHODS

We searched MEDLINE, Embase, the Science Citation Index and the National Institute for Health Research Health Technology Assessment Database on 4 March 2016. We screened references in the included studies to identify additional studies. We also conducted citation searches of relevant studies, most recently on 4 December 2016. We did not restrict studies by language or publication status, or whether data were collected prospectively or retrospectively.

SELECTION CRITERIA

We included diagnostic accuracy studies that evaluated at least one of the index tests (urea breath test using isotopes such as 13C or 14C, serology and stool antigen test) against the reference standard (histopathological examination using H & E stain, special stains or immunohistochemical stain) in people suspected of having H pylori infection.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the references to identify relevant studies and independently extracted data. We assessed the methodological quality of studies using the QUADAS-2 tool. We performed meta-analysis by using the hierarchical summary receiver operating characteristic (HSROC) model to estimate and compare SROC curves. Where appropriate, we used bivariate or univariate logistic regression models to estimate summary sensitivities and specificities.

MAIN RESULTS

We included 101 studies involving 11,003 participants, of which 5839 participants (53.1%) had H pylori infection. The prevalence of H pylori infection in the studies ranged from 15.2% to 94.7%, with a median prevalence of 53.7% (interquartile range 42.0% to 66.5%). Most of the studies (57%) included participants with dyspepsia and 53 studies excluded participants who recently had proton pump inhibitors or antibiotics.There was at least an unclear risk of bias or unclear applicability concern for each study.Of the 101 studies, 15 compared the accuracy of two index tests and two studies compared the accuracy of three index tests. Thirty-four studies (4242 participants) evaluated serology; 29 studies (2988 participants) evaluated stool antigen test; 34 studies (3139 participants) evaluated urea breath test-13C; 21 studies (1810 participants) evaluated urea breath test-14C; and two studies (127 participants) evaluated urea breath test but did not report the isotope used. The thresholds used to define test positivity and the staining techniques used for histopathological examination (reference standard) varied between studies. Due to sparse data for each threshold reported, it was not possible to identify the best threshold for each test.Using data from 99 studies in an indirect test comparison, there was statistical evidence of a difference in diagnostic accuracy between urea breath test-13C, urea breath test-14C, serology and stool antigen test (P = 0.024). The diagnostic odds ratios for urea breath test-13C, urea breath test-14C, serology, and stool antigen test were 153 (95% confidence interval (CI) 73.7 to 316), 105 (95% CI 74.0 to 150), 47.4 (95% CI 25.5 to 88.1) and 45.1 (95% CI 24.2 to 84.1). The sensitivity (95% CI) estimated at a fixed specificity of 0.90 (median from studies across the four tests), was 0.94 (95% CI 0.89 to 0.97) for urea breath test-13C, 0.92 (95% CI 0.89 to 0.94) for urea breath test-14C, 0.84 (95% CI 0.74 to 0.91) for serology, and 0.83 (95% CI 0.73 to 0.90) for stool antigen test. This implies that on average, given a specificity of 0.90 and prevalence of 53.7% (median specificity and prevalence in the studies), out of 1000 people tested for H pylori infection, there will be 46 false positives (people without H pylori infection who will be diagnosed as having H pylori infection). In this hypothetical cohort, urea breath test-13C, urea breath test-14C, serology, and stool antigen test will give 30 (95% CI 15 to 58), 42 (95% CI 30 to 58), 86 (95% CI 50 to 140), and 89 (95% CI 52 to 146) false negatives respectively (people with H pylori infection for whom the diagnosis of H pylori will be missed).Direct comparisons were based on few head-to-head studies. The ratios of diagnostic odds ratios (DORs) were 0.68 (95% CI 0.12 to 3.70; P = 0.56) for urea breath test-13C versus serology (seven studies), and 0.88 (95% CI 0.14 to 5.56; P = 0.84) for urea breath test-13C versus stool antigen test (seven studies). The 95% CIs of these estimates overlap with those of the ratios of DORs from the indirect comparison. Data were limited or unavailable for meta-analysis of other direct comparisons.

AUTHORS' CONCLUSIONS

In people without a history of gastrectomy and those who have not recently had antibiotics or proton ,pump inhibitors, urea breath tests had high diagnostic accuracy while serology and stool antigen tests were less accurate for diagnosis of Helicobacter pylori infection.This is based on an indirect test comparison (with potential for bias due to confounding), as evidence from direct comparisons was limited or unavailable. The thresholds used for these tests were highly variable and we were unable to identify specific thresholds that might be useful in clinical practice.We need further comparative studies of high methodological quality to obtain more reliable evidence of relative accuracy between the tests. Such studies should be conducted prospectively in a representative spectrum of participants and clearly reported to ensure low risk of bias. Most importantly, studies should prespecify and clearly report thresholds used, and should avoid inappropriate exclusions.

Evaluation of a new fluorescence quantitative PCR test for diagnosing Helicobacter pylori infection in children

Background

Numerous diagnostic tests are available to detect Helicobactor pylori (H. pylori). There has been no single test available to detect H. pylori infection reliably. We evaluated the accuracy of a new fluorescence quantitative PCR (fqPCR) for H. pylori detection in children.

Methods

Gastric biopsy specimens from 138 children with gastritis were sent for routine histology exam, rapid urease test (RUT) and fqPCR. ¹³C-urea breath test (¹³C-UBT) was carried out prior to endoscopic procedure. Gastric fluids and dental plaques were also collected for fqPCR analysis.

Results

38 children (27.5%) were considered positive for H. pylori infection by gold standard (concordant positive results on 2 or more tests). The remaining 100 children (72.5%) were considered negative for H. pylori. Gastric mucosa fqPCR not only detected all 38 H. pylori positive patients but also detected 8 (8%) of the 100 gold standard-negative children or 11 (10.7%) of the 103 routine histology-negative samples. Therefore, gastric mucosa fqPCR identified 46 children (33.3%) with H. pylori infection, significantly higher than gold standard or routine histology (P<0.01). Both gastric fluid and dental plaque fqPCR only detected 32 (23.2%) and 30 (21.7%) children with H. pylori infection respectively and was significantly less sensitive than mucosa fqPCR (P<0.05) but was as sensitive as non-invasive UBT.

Conclusions

Gastric mucosa fqPCR was more sensitive than routine histology, RUT, ¹³C-UBT alone or in combination to detect H. pylori infection in children with chronic gastritis. Either gastric fluid or dental plaque PCR is as reliable as ¹³C-UBT for H. pylori detection.

An optimized 13C-urea breath test for the diagnosis of H pylori infection

AIM: To validate an optimized 13C-urea breath test (¹³C-UBT) protocol for the diagnosis of H pylori infection that is cost-efficient and maintains excellent diagnostic accuracy.

METHODS: 70 healthy volunteers were tested with two simplified ¹³C-UBT protocols, with test meal (Protocol 2) and without test meal (Protocol 1). Breath samples were collected at 10, 20 and 30 min after ingestion of 50 mg ¹³C-urea dissolved in 10 mL of water, taken as a single swallow, followed by 200 mL of water (pH 6.0) and a circular motion around the waistline to homogenize the urea solution. Performance of both protocols was analyzed at various cut-off values. Results were validated against the European protocol.

RESULTS: According to the reference protocol, 65.7% individuals were positive for H pylori infection and 34.3% were negative. There were no significant differences in the ability of both protocols to correctly identify positive and negative H pylori individuals. However, only Protocol 1 with no test meal achieved accuracy, sensitivity, specificity, positive and negative predictive values of 100%. The highest values achieved by Protocol 2 were 98.57%, 97.83%, 100%, 100% and 100%, respectively.

CONCLUSION: A 10 min, 50 mg ¹³C-UBT with no test meal using a cut-off value of 2-2.5 is a highly accurate test for the diagnosis of H pylori infection at a reduced cost.

13C-urea breath test during hospitalization for the diagnosis of Helicobacter pylori infection in peptic ulcer bleeding

OBJECTIVE

To evaluate the accuracy of (13)C-urea breath test (UBT) to detect Helicobacter pylori infection in patients hospitalized with peptic ulcer bleeding and treated with proton pump inhibitors (PPIs).

METHODS

Patients hospitalized with peptic ulcer bleeding, and treated with omeprazole, had a first UBT performed the day after resuming oral feeding. Patients with a negative UBT during hospitalization underwent a repeated UBT 15 days after stopping PPIs.

RESULTS

The first UBT during hospitalization was positive in 86% of 131 patients. Time between admission and performance of the test was longer in patients with negative versus positive UBT (5.2 +/- 0.7 versus 4.3 +/- 0.5 days; p < .001). The repeated UBT became positive in 15 of 18 (83%) patients with a negative first UBT. In the multivariate analysis, the only variable associated with a negative first UBT was the time elapsed between admission and performance of the test (odds ratio = 6.6; 95%CI = 2.9-15.1).

CONCLUSION

Most H. pylori-positive patients with ulcer bleeding have a positive UBT (performed just after resuming oral feeding) despite previous treatment with high-dose PPIs. Nevertheless, to preclude false-negative results due to PPI therapy, the UBT should be performed as early as possible. If the infection cannot be demonstrated with this first UBT, H. pylori still needs to be definitively excluded with a second UBT performed after stopping PPIs.

Long-term follow-up of 13C-urea breath test results after Helicobacter pylori eradication: frequency and significance of borderline delta13CO2 values

BACKGROUND

The precise choice of cut-off point for the 13C-urea breath test to define whether it is positive or negative represents a controversial issue.

AIM

To quantify the 13C-urea breath test result for several years following Helicobacter pylori eradication, and to evaluate the frequency and the significance of borderline delta13CO2 values.

METHODS

Two-hundred H. pylori eradicated patients confirmed by 13C-urea breath test (100 mg of urea, citric acid), and having had repeated this test yearly up to 5 years, were studied. Delta13CO2 values between 2 and 5/1000 were considered as borderline results.

RESULTS

Eight H. pylori recurrences were observed during 406 patient-years of follow-up (1.97% yearly). In two of eight reinfected patients, the reinfection was preceded by a negative delta13CO2 value >2/1000. Borderline delta13CO2 values were detected in 4% of the 606 urea breath tests performed, and in 25% when only patients in whom H. pylori recurrence was detected in subsequent urea breath tests were included (P < 0.05). The negative-predictive value of a post-treatment delta13CO2 >2/1000 for the diagnosis of H. pylori recurrence was 99%.

CONCLUSIONS

Positive and negative urea breath test results tend to cluster outside the range between 2/1000 and 5/1000. Nevertheless, a borderline urea breath test delta value (e.g. very close to the selected cut-off point) should be interpreted cautiously, and the result should probably be confirmed either by repeating the urea breath test or by other diagnostic methods. On the contrary, a delta13CO2 value <2/1000 very confidently confirms H. pylori eradication.

Analytical techniques in biomedical stable isotope applications: (isotope ratio) mass spectrometry or infrared spectrometry?

An overview is presented of biomedical applications of stable isotopes in general, but mainly focused on the activities of the Center for Liver, Digestive and Metabolic Diseases of the University Medical Center Groningen. The aims of metabolic studies in the areas of glucose, fat, cholesterol and protein metabolism are briefly explained, as well as the principle of breath testing and the techniques to study body composition and energy expenditure. Much attention is paid to the analytical considerations based upon metabolite concentrations, sample size restrictions, the availability of stable isotope labelled substrates and dose requirements in relation to compound-specific isotope analysis. The instrumental advantages and limitations of the generally used techniques gas chromatography/reaction/isotope ratio mass spectrometry and gas chromatography/mass spectrometry are described as well as the novelties of the recently commercialised liquid chromatography/combustion/isotope ratio mass spectrometry. The present use and future perspective of infrared (IR) spectrometry for clinical and biomedical stable isotope applications are reviewed. In this respect, the analytical demands on IR spectrometry are discussed to enable replacement of isotope ratio mass spectrometry by IR spectrometry, in particular, for the purpose of compound-specific isotope ratio analysis in biological matrices.

Major influence of oxygen supply on 13CO2:12CO2 ratio measurement by nondispersive isotope-selective infrared spectroscopy

BACKGROUND

The nondispersive isotope-selective infrared spectroscopy (NDIRS) is a valid method for the measurement of the 13CO2:12CO2 ratio in breath samples. Methodical influences have to be considered to obtain valid results.

AIM

To evaluate the effect of oxygen supply to patients on the measurement of 13C:12C ratio in breath samples by NDIRS.

METHODS

Breath samples of 26 healthy volunteers were taken before, immediately after, and 5 minutes after inhalation of 100% oxygen via a continuous positive air pressure (CPAP) mask. Analysis of breath samples was performed by NDIRS.

RESULTS

Delta per thousand before oxygen inhalation was -25.8 +/- 0.2. Immediately after 5 minutes of 100% oxygen inhalation, delta per thousand increased to -14.8 +/- 0.5 (delta over baseline [DOB] 11.0 +/- 0.4) and after additional 5 minutes of room air inhalation, delta per thousand normalized to -25.6 +/- 0.2 (DOB 0.2 +/- 0.1).

CONCLUSIONS

Oxygen supply to patients and, therefore, changes in gas composition in breath samples clearly influence 13CO2 measurement by NDIRS. This has to be taken into account in the clinical setting. Thus, oxygen supply during measurement of exhaled 13CO2 by NDIRS has to be avoided or maintained at a strictly constant level.

Rifabutin based triple therapy for eradication of H. pylori primary and secondary resistant to tinidazole and clarithromycin

BACKGROUND

Rifabutin has been empirically used in Helicobacter pylori infections resistant to triple therapy. There are no data on primary and secondary resistance to rifabutin and its use in specific cases.

AIM

To analyse the susceptibility and resistance to rifabutin in H. pylori-positive patients with or without previous H. pylori therapy and to test the efficacy of rifabutin in H. pylori resistant to clarithromycin and tinidazole.

METHODS

Four hundred and twenty H. pylori-positive patients without previous exposure to triple therapy and 104 patients who had already received one course of triple therapy underwent upper endoscopy for dyspeptic symptoms and H. pylori susceptibility test. Amoxicillin, clarithromycin, tinidazole and rifabutin were evaluated for resistance and susceptibility. Forty patients with primary resistance to both clarithromycin and tinidazole and with susceptibility to amoxicillin and rifabutin, and 65 patients with secondary resistance and susceptibility to the same antibiotics were identified. All these patients received a 10-day triple therapy with pantoprazole amoxicillin and rifabutin. Treatment success was evaluated by the 13C-Urea Breath test.

RESULTS

In naive patients 23% of strains were resistant to clarythromycin, 35% to tinidazole, 9% to both antibiotics, and none was resistant to rifabutin In patients already treated the percentages of resistant strains were 76, 64.4, 62.5 and 1%, respectively. With rifabutin based triple therapy eradication rates were (Per Protocol and Intention-to-Treat analysis) 100 and 87.5% in primary resistance to clarithromycin and tinidazole and 82.2 and 78.5% in secondary resistance.

CONCLUSION

H. pylori primary and secondary resistances to clarithromycin and tinidazole are high in our geographic area, while resistance to rifabutin is rare. Rifabutin-based triple therapy, can be successfully used in primary and secondary resistance to clarithromycin and tinidazole according to the in vitro susceptibility test.

The early effect of proton pump inhibitor therapy on the accuracy of the 13C-urea breath test

BACKGROUND

The intake of proton pump inhibitors may interfere with the reliability of the urea breath test.

AIM

Prospective study to assess the accuracy of the urea breath test during the first days of therapy with proton pump inhibitors.

PATIENTS

Thirty patients who needed to start proton pump inhibitors therapy and 53 volunteers.

METHODS

A 13C-urea breath test was performed respectively before starting proton pump inhibitors therapy and every morning before its intake up until 10 days. The test was considered positive for values of 13CO2 > or = 3.0% delta over baseline. The coefficient of reproducibility for 95% interval of confidence of the urea breath test was calculated in both groups.

RESULTS

Of the 30 patients receiving proton pump inhibitors, 47% were positive for Helicobacter pylori. Among these, 43% developed false negative breath tests in the first 10 days. False positive results occurred in 37.5% of H. pylori-negative subjects in the first 10 days. The coefficient of reproducibility of the urea breath test was significantly higher in the group treated with proton pump inhibitors (11.0 versus 1.8 for the control group, p < 0.0001).

CONCLUSION

The intake of proton pump inhibitors impairs the accuracy of the 13C-urea breath test. False negative and false positive 13C-urea breath tests are common, occur as soon as after 1 day and increase with prolonged duration of treatment. The coefficient of reproducibility of the test in patients receiving proton pump inhibitors is not acceptable for clinical purpose and the test should not be performed once the medication has been started.

Review article: 13C-urea breath test in the diagnosis of Helicobacter pylori infection -- a critical review

The urea breath test is a non-invasive, simple and safe test which provides excellent accuracy both for the initial diagnosis of Helicobacter pylori infection and for the confirmation of its eradication after treatment. Some studies have found no differences between urea breath test performed under non-fasting conditions. The simplicity, good tolerance and economy of the citric acid test meal probably make its systematic use advisable. The urea breath test protocol may be performed with relatively low doses (<100 mg) of urea: 75 mg or even 50 mg seem to be sufficient. With the most widely used protocol (with citric acid and 75 mg of urea), excellent accuracy is obtained when breath samples are collected as early as 10-15 min after urea ingestion. A unique and generally proposed cut-off level is not possible because it has to be adapted to different factors, such as the test meal, the dose and type of urea, or the pre-/post-treatment setting. Fortunately, because positive and negative urea breath test results tend to cluster outside of the range between 2 and 5 per thousand, a change in cut-off value within this range would be expected to have little effect on clinical accuracy of the test.

[Comparison between two 13C-urea breath tests for the diagnosis of Helicobacter pylori infection: isotope ratio mass spectrometer versus infrared spectrometer]

OBJECTIVES

To compare the accuracy of the breath test using the isotope ratio mass spectrometer (IRMS) versus the nondispersive isotope-selective infrared spectrometer (NDIRS) in the diagnosis of Helicobacter pylori infection.

METHOD

Multicenter study in 4 Spanish hospitals. One group of dyspeptic patients who had not undergone prior eradication therapy and another group of patients with gastric ulcer or gastrointestinal bleeding due to gastroduodenal ulcer receiving H. pylori eradication therapy were included in the study. A reference standard based on histology and the rapid urease test was used. The breast test (TAU-KIT, Isomed S.L., Madrid, Spain) was performed with citric acid and 100 mg of 13C-urea. Samples of expired air were collected in tubes and bags for reading with the IRMS (ABCA, PDZ, Crewe, Manchester, England) and the NDIRS (UBiT-IR200, Otsuka Electronics, Co, Osaka, Japan), respectively. The endoscopist, pathologist and person responsible for reading the urease test and both breath tests were blinded to the results of the other diagnostic methods.

RESULTS

Forty-one patients were included. The prevalence of H. pylori was 26%. No differences were found on comparing the mean values obtained with the IRMS and the NDIRS: 13 (standard deviation) (24) and 14 (25) delta units, respectively. The area under the ROC curve for the IRMS and the NDIRS was 0.96. The diagnostic accuracy for the best cut-off point with the IRMS and the NDIRS was, respectively: sensitivity (90 and 100%), specificity (96 and 89%), positive predictive value (90 and 77%), negative predictive value (96 and 100%), + likelihaod ratio (25 and 9.3) and (0.1 and 0). A close correlation was found between the values of the IRMS and those of the NDIRS (lineal regression equation, Y = 1.1 + 1.004. X; r = 0.97).

CONCLUSION

Both the spectrometers used to evaluate the breath test, the IRMS and the NDIRS, offer a high degree of accuracy in the diagnosis of H. pylori infection.

Endoscopic 13C-urea breath test for the diagnosis of Helicobacter pylori infection

BACKGROUND

Endoscopic 13C-urea breath test may avoid contamination of oral urease and rapidly discriminate Helicobacter pylori-positive and Helicobacter pylori-negative patients.

AIMS

To compare the accuracy of endoscopic 13C-urea breath test with conventional invasive methods in diagnosis of Helicobacter pylori infection.

PATIENTS

One hundred patients who attended for routine upper gastrointestinal endoscopy were included.

METHODS

13C-urea was applied to the stomach through the working channel of endoscope at the end of endoscopic examination. Breath samples were collected before endoscopy and 2, 4, 6, 8, 10 min after consumption of 100 or 50 mg 13C-urea. Helicobacter pylori infection was defined as those with positive culture or positive results of both histology and CLO test.

RESULTS

The accuracy of 100 mg endoscopic 13C-urea breath test was significantly higher than that of culture and CLO test (100% vs. 88% and 92%, p = 0.02 and 0.03, respectively). The accuracy of 50 mg endoscopic 13C-urea breath test was higher than that of histology and CLO test (98% vs. 90% and 96%, respectively), although the differences were not statistically significant.

CONCLUSIONS

Endoscopic 13C-urea breath test has a higher accuracy compared with biopsy-based modalities. It may be a good choice to diagnose Helicobacter pylori infection if endoscopy is indicated for a dyspeptic patient.

A quantitative evaluation of spurious results in the infrared spectroscopic measurement of CO2 isotope ratios

The possible generation of spurious results, arising from the application of infrared spectroscopic techniques to the measurement of carbon isotope ratios in breath, due to coincident absorption bands has been re-examined. An earlier investigation, which approached the problem qualitatively, fulfilled its aspirations in providing an unambiguous assurance that 13C16O2/12C16O2 ratios can be confidently measured for isotopic breath tests using instruments based on infrared absorption. Although this conclusion still stands, subsequent quantitative investigation has revealed an important exception that necessitates a strict adherence to sample collection protocol. The results show that concentrations and decay rates of the coincident breath trace compounds acetonitrile and carbon monoxide, found in the breath sample of a heavy smoker, can produce spurious results. Hence, findings from this investigation justify the concern that breath trace compounds present a risk to the accurate measurement of carbon isotope ratios in breath when using broadband, non-dispersive, ground state absorption infrared spectroscopy. It provides recommendations on the length of smoking abstention required to avoid generation of spurious results and also reaffirms, through quantitative argument, the validity of using infrared absorption spectroscopy to measure CO2 isotope ratios in breath.