Refinement of the 14C-urea breath test for detection of Helicobacter pylori

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.

Comparison of the performance of serological kits for Helicobacter pylori infection with European and Asian study populations

Most commercial kits for the detection of Helicobacter pylori were developed and validated with Western populations, and some have been found to perform less well with Asian populations. This study compared the performances of three serological kits with Swedish and Vietnamese peptic ulcer patients and asymptomatic individuals. The Pyloriset EIA-GIII and HM-CAP ELISA kits indicated that Asian populations had lower antibody titres to H. pylori than European populations. Despite the difference, the Pyloriset EIA-GIII kit performed well with Vietnamese peptic ulcer patients and population controls. The HM-CAP ELISA kit had a significantly lower performance with Asian populations that could not be improved by adjustments to the cut-off level. The Helicoblot 2.1 immunoblot kit performed equally well with Vietnamese and Swedish populations, although the response rate to the 35-kDa band was significantly lower with Vietnamese individuals.

Changes in gastric environment with test meals affect the performance of 14C-urea breath test

BACKGROUND

(14)C-urea breath test (UBT) is considered to be an accurate diagnostic test for the detection of active Helicobacter pylori infection. Various test meals are used in (14)C-UBT to slow down gastric emptying, and to enhance the gastric distribution, in order to increase the time and area of contact between microorganisms and the tracer substrate. The aim of the present paper was to evaluate the effect of gastric environment on the performance of (14)C-UBT using an alkaline and an acidic liquid test meal having gastric emptying retardant effect.

METHODS

The comparison of (14)C-UBT was done with liquid test meals (200 mL water) comprising (i) plain drinking water (PDW); (ii) 1.3 g or 3.0 g citric acid (CA); and (iii) 3.0 g trisodium citrate (TSC). Eighteen patients (37 +/- 12 years, range 18-57 years) with complaints of dyspepsia participated in the study. The status of H. pylori was confirmed by histology and rapid urease test. A total of 93 kBq of (14)C-urea (0.5 mL) in a gelatin capsule was orally administered along with liquid test meals to the overnight fasting subjects. Breath samples were collected and radioactivity measured. Results were expressed as (14)CO(2)/mmol exhaled CO(2) as percentage of administered radioactive urea.

RESULTS

Higher acidic gastric environment (pH approx. 2.0) with CA was found to increase the exhaled (14)CO(2) level in a dose-dependent manner as compared to PDW and TSC meal (P < 0.05) at all time points. With TSC test meal, the expired (14)CO(2) level decreased in the lower acidic gastric environment (pH approx. 5.3). The peaks of exhaled (14)CO(2) with TSC test meal were observed at the same time points as that with PDW and CA test meals. The (14)C-UBT with TSC was found to be positive in 77% of patients (10/13).

CONCLUSION

Better interaction between the microbial urease and (14)C-urea, caused by a test meal that retards gastric emptying and that changes gastric pH, plays an important role in hydrolysis of the administered (14)C-urea by H. pylori urease.

Enzyme-linked immunosorbent assay for Helicobacter pylori needs adjustment for the population investigated

Helicobacter pylori infection and peptic ulcer disease are common in developing countries, e.g., Vietnam. An enzyme-linked immunosorbent assay (ELISA) for screening of patients and for seroepidemiology is a useful tool but needs to be validated in the population studied. We used in-house ELISA with sonicated Swedish and Vietnamese strains as antigens to measure immunoglobulin G antibodies after absorption with sonicated Campylobacter jejuni in sera from 270 H. pylori culture-confirmed peptic ulcer patients, 128 Swedish urea-breath test and immunoblot-positive healthy controls, and 432 Vietnamese immunoblot-positive population controls. Sonicated whole-cell antigen based on the local strains showed a significantly better performance. Immunoblot-positive peptic ulcer patients had significantly higher antibody concentrations than immunoblot-positive population controls, necessitating a lower cutoff level if serology is used for screening or epidemiological purposes. The study shows that the parameters of ELISA for H. pylori need to be adjusted for the population being investigated.

Best cut-off values for [14C]-urea breath tests for Helicobacter pylori detection

BACKGROUND

The 'test and treat' strategy for Helicobacter pylori is recommended in dyspeptic patients under 55 years of age with no alarm symptoms. Reliable non-invasive tests are therefore needed. The aim of this study was to assess the pre- and post-treatment accuracy of a low dose (1 microCi [37kBq]), short collecting time [14C]-UBT (urea breath test) in diagnosing H pylori infection, examining different methods to analyse the best cut-off points.

METHODS

The study included 119 patients. Endoscopy and [14C]-UBT were performed in the pre- and post-treatment setting. [14C]-UBT results were expressed in three different ways: 1) the measured disintegrations per minute (dpm) at sample time, 2) the difference (D) in dpm between sample time and the dpm at T0, 3) the ratio of dpm at sample time to dpm at T0.

RESULTS

Seventy-six out of the 119 patients (63.9%; 95% CI: 54.9 to 71.9) were infected. Seventy-three (96%) patients completed the follow-up. The most accurate results in both pre- (sensitivity 95.9%; specificity 97.7%) and post-treatment (sensitivity 90.9%; specificity 100%) were obtained using the difference (D) in dpm between sample time at T0 and at T12.5.

CONCLUSION

A low dose [14C]-UBT, with a short collecting time, is a reliable method to evaluate H. pylori infection in both the pre- and post-treatment setting.

Helicobacter pylori: a microbiologist's view

Helicobacter pylori infection is known to cause a number of gastrointestinal diseases. From the standpoint of a microbiologist there are several important facets to this organism, which include the nature of the organism, it's diagnosis and the effectiveness of eradication therapy.

Epidemiology and diagnosis of Helicobacter pylori infection

There have been no major breakthroughs in the field of epidemiology and diagnosis of Helicobacter pylori infection over the last year, thus for this reason, these two topics will be treated in the same chapter. Information on the incidence of infection, as in the study of Malaty et al. are now being published from long-term cohort follow-ups. The route of transmission of H. pylori remains controversial, with circumstantial evidence for infection via exposure to animals, contaminated water supplies and oral reservoirs being reported. The value of citric acid to improve urea breath test (UBT) results has been documented. A novel stool test has been released on the market and we are awaiting more information, while detection of antibodies in urine gave satisfactory results. However, the most interesting data comes from the study of McColl et al. who clearly proved on a large sample and a 1-year follow-up that the 'test and treat' strategy using UBT, as proposed in the Maastricht Consensus Report, is definitely the method to use.

Validated accuracy of a novel urea breath test for rapid Helicobacter pylori detection and in-office analysis

BACKGROUND

A novel 14C-urea breath test (UBT) was developed to detect the presence of Helicobacter pylori by bench analysis in office, enabling the practitioner to readily reveal H. pylori infection.

AIM

To validate the novel UBT (Heliprobe) versus conventional UBT.

METHODS

Pretreatment (n = 203) and post-treatment (n = 147) detection of H. pylori. Additional tests with encapsulated 14C-urea (n = 37) were validated. After intake of liquid or encapsulated 14C-urea, exhaled 14CO2 in breath was trapped in benzethoniumhydroxide/ethanol, or adsorbed to LiOH-soaked pads on a dry cover surface (Heliprobe BreathCard). The amount of adsorbed 14C was detected using a beta-scintillator or two Geiger-Müller counters operating in parallel (Heliprobe Analyzer).

RESULTS

For pretreatment detection, we found full concordance between the UBTs, with 100% sensitivity and specificity (CI 95-100% and 97-100%, respectively) and strong agreement (r = 0.80, CI 0.75-0.85; kappa = 1, CI 0.86-1.14; P < 0.0001). Similarly, for post-treatment follow-up detection, sensitivity and specificity were 100% (CI 85-100% and 97-100%, respectively) with significant agreement (r = 0.48, CI 0.34-0.59; kappa = 1, CI 0.84-1.16; P < 0.0001). The use of encapsulated 14C-urea did not change agreement between the tests. Sensitivity and specificity were 100% (CI 72-100% and 87-100%, respectively) with strong agreement between the tests (r = 0.71, CI 0.50-0.84; kappa = 1, CI 0.68-1.32; P < 0.0001).

CONCLUSION

The novel Heliprobe UBT, with either liquid or encapsulated 14C-urea, seems equi-efficacious to conventional UBT in fulfilling its role as the non-invasive gold standard for detection of H. pylori.