Prospective evaluation of the diagnostic performance of a new Helicobacter pylori stool antigen immunochromatographic test

Vikram Kate; Mohsina Subair; Ashok Kumar Sahoo; Namrata Bhosale; Madhuvanthi Karthikeyan; Jharna Mandal; Sathasivam Suresh Kumar; Mahalakshmy Thulasingam

doi:10.4103/jmgims.jmgims_32_18

ORIGINAL ARTICLE

Year : 2019 | Volume : 24 | Issue : 1 | Page : 23-27

Prospective evaluation of the diagnostic performance of a new Helicobacter pylori stool antigen immunochromatographic test

Vikram Kate¹, Mohsina Subair¹, Ashok Kumar Sahoo¹, Namrata Bhosale², Madhuvanthi Karthikeyan¹, Jharna Mandal², Sathasivam Suresh Kumar¹, Mahalakshmy Thulasingam³
¹ Department of Surgery, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India
² Department of Microbiology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India
³ Department of Preventive and Social Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India

Date of Web Publication

14-Mar-2019

Correspondence Address:
Dr. Vikram Kate
Professor of General and Gastrointestinal Surgery, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry - 605 006
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jmgims.jmgims_32_18

Abstract

Introduction: Stool-based immunochromatographic test (ICT) requires validation for use in regional setups. Hence, this study was carried out to evaluate the diagnostic performance of a newly developed ICT kit (Pylori-Strip/Pylori K-Set, Corisbio). Materials and Methods: This was a prospective analytical study on patients who underwent upper gastrointestinal endoscopy. The combination of histology and urease was used as gold standard. Stool specimens were subjected to immunochromatographic stool antigen test using Corisbio stool antigen kit. The diagnostic performance of cassette and dipstick method and combination both was compared to the gold standard. Correlation of test efficacy with endoscopic, histological, and demographic parameters was carried out. Results: A total of 143 patients were included in the study. The diagnostic performance of cassette method and dipstick method was sensitivity, 73.3% (22/30) and 73.3% (22/30); specificity, 97.3% (110/113) and 98.23% (111/113); positive predictive value (PPV), 88% (22/25) and 91.66% (22/24); negative predictive value (NPV), 93.22% (110/118) and 93.27% (111/119); and overall accuracy, 92.3% (132/143) and 93% (133/143), respectively, when compared with the gold standard. The combination of the tests had a sensitivity of 73.3% (22/30), specificity of 97.3% (110/113), PPV of 88% (22/25), NPV of 93.22% (110/118), and accuracy of 92.3% (132/143). The diagnostic performance of the kit was unaffected by various demographic, endoscopic, or histological characteristics. Conclusions: The stool-based ICT is rapid and noninvasive diagnostic test with a high specificity, PPV and NPV, and overall accuracy. However, as the sensitivity is low, it should be primarily used as a rapid office test to determine eradication of Helicobacter pylori.

Keywords: Cassette method, diagnosis of Helicobacter pylori, Helicobacter pylori eradication, dipstick method, immunochromatography

How to cite this article:
Kate V, Subair M, Sahoo AK, Bhosale N, Karthikeyan M, Mandal J, Kumar SS, Thulasingam M. Prospective evaluation of the diagnostic performance of a new Helicobacter pylori stool antigen immunochromatographic test. J Mahatma Gandhi Inst Med Sci 2019;24:23-7

How to cite this URL:
Kate V, Subair M, Sahoo AK, Bhosale N, Karthikeyan M, Mandal J, Kumar SS, Thulasingam M. Prospective evaluation of the diagnostic performance of a new Helicobacter pylori stool antigen immunochromatographic test. J Mahatma Gandhi Inst Med Sci [serial online] 2019 [cited 2023 Mar 29];24:23-7. Available from: https://www.jmgims.co.in/text.asp?2019/24/1/23/254125

Introduction

Early identification and eradication of Helicobacter pylori are important, and there is a need for reliable means of diagnosis.^[1],[2] Methods for the diagnosis of H. pylori can be classified as invasive and noninvasive.^[3] The invasive methods are based on the demonstration of the organism from gastric endoscopic biopsy samples by histopathological staining, rapid urease test, or culture of the organism. The noninvasive methods, which require no endoscopic examination, include serological methods, urea breath test (UBT), and stool-based tests (SBT).^[4],[5]

The SBTs, developed based on the evidence of fecal-oral transmission, are becoming more popular owing to the noninvasive nature rapidity of results. Many new SBTs have been developed, which can be either ELISA immunoassay (EIA) or immunochromatographic test (ICT).^[6],[7] The need for specialized equipment and the delay in results in EIA have made ICT assay the preferred tool and are being considered the preferable strategy for diagnosis of H. pylori in primary care in few reports.^[7],[8] However, the diagnostic accuracy of immunochromatographic SBT requires validation for use in regional setups as a wide variation in the diagnostic performance has been reported with geographical variation, prevalence of H. pylori, reference methods utilized, antigen used in the kit, and antigenicity of the H. pylori strain.^[7] The data on the diagnostic efficacy of stool antigen kits on Indian population are also sparse. Hence, this study was carried out to evaluate the diagnostic performance of stool antigen immunochromatography test (Pylori-Strip/Pylori K-Set, Corisbio) for detection of H. pylori infection.^[9]

Materials and Methods

Study design

The study was a prospective clinical analytical study carried out in the department of surgery of a tertiary care institute from January 2014 to February 2016. Institute Human Ethics Committee approvals and written informed consent were obtained from the participants.

Patients

All consecutive patients aged 18–70 years who underwent upper gastrointestinal endoscopy (UGIE) for the evaluation of upper gastrointestinal (UGI) disorders during the study period were included in the study. Patients with suspicious/proven upper gastrointestinal malignancy, prior antibiotic therapy or prior anti-H. pylori therapy, history of use of proton-pump inhibitors (PPIs) within 6 weeks, and acute UGI bleeding were excluded from the study.

Study procedure

All recruited patients underwent UGIE with video endoscope (EG-290kp; Pentax, Montvale, NJ, USA) by an experienced endoscopist under topical anesthesia (2% lignocaine spray). Four endoscopic biopsy samples were taken, two each from the gastric corpus and antrum. Urease test was done on two samples using urea solution prepared and standardized in the institute.^[10] Histology was done by Giemsa staining on the other two samples. The combination of these two was used as a gold standard for the diagnosis of H. pylori infection.^[11] If either or both the tests were positive, the patient was considered to be positive for H. pylori, and if both the tests were negative, the patient was considered negative.

Stool samples were collected and stored at 2°C–8°C for a maximum period of up to 24 h. These were analyzed using the H. pylori stool ICT (Corisbio kit) by an investigator blinded to the H. pylori status of the patient. The assay was based on the antigen HSPb58kDa. Stool samples were tested using cassette (K-set) and dipstick method of the kit [Figure 1].

Figure 1: Corisbio-stool antigen kit; cassette method (black arrow); dipstick method (blue arrow)

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Test procedure by cassette method

The fecal sampling system (FSS) tube of the kit comprised a capped tube with a screw attached to the cap. The screw was used for sample collection, maintaining the dilution ratio of 4% w/v. About 80 μL of sample was pipetted using a micropipette into the FSS vial. The re-capped tube was then gently vortexed to homogenize the stool specimen. The tip of the cap was then broken, and four drops of diluted sample were dispensed into the sample well at room temperature and were read after ten minutes.

Test procedure by dipstick method

The FSS for this method comprised a plastic loop (10 μL). The specimen was mixed with 0.5 ml (15 drops) of dilution buffer by dipping the loop containing the stool sample into the tube, maintaining the dilution ratio of 4% w/v. For liquid samples, two loops of 10 μL were taken; for solid samples, one loop was taken. The preparation in the test tube was then gently vortexed to homogenize the stool specimen. The sensitized strip was dipped in the solution and was read after 10 min.

Reading cassette and dipstick tests

The tests were read independently by two investigators who were blinded to the H. pylori status of the patient. The test was considered to be negative if only a green line appeared at the control line (C) position of the reading window. Appearance of a reddish-purple band or even a weak reddish-purple line at the test line (T) position of the reading window along with the green line was considered as positive. The absence of a control line was considered as an invalid test. For the combination of cassette and dipstick methods, the test was taken as positive when either or both were positive and negative when both were negative.

Outcomes

The primary outcome was to evaluate the diagnostic performance of the cassette, dipstick, and the combination of the two methods when compared to gold standard (combination of histology and rapid urease test) in terms of sensitivity, specificity, positive predictive value, negative predictive value, and accuracy. The secondary outcome was the correlation of the diagnostic performance of the cassette, dipstick, and combination of the two tests with various demographic, endoscopic, and histological characteristics of the patients.

Statistical analysis

Statistical analysis was carried out using SPSS software version 19 (IBM SPSS Statistics for Windows, Armonk, NY, IBM Corp., USA) for Windows. The sample size of 130 was calculated to detect sensitivity and specificity of 90% with an alpha error of 5%.^[1] Expecting a 10% dropout, the sample size was rounded off to 145.^[11] The sensitivity, specificity, positive and negative predictive value, and accuracy were calculated using the standard formulae.

Results

Among the 143 patients included in the study, 30 were positive for H. pylori by gold standard method (overall prevalence of 20.9%). The sensitivity and specificity of K-set and dipstick methods when compared to the gold standard were 73.33%, 97.33% and 73.33%, 98.23%, respectively. K-set and dipstick had concordant results in all cases except for one case which was accurately identified as negative by dipstick and falsely identified as positive by K-set. The diagnostic performance for detection of H. pylori of K-set, dipstick, and the combination of both in comparison to gold standard is shown in [Table 1].

Table 1: Diagnostic performance of K-set, dipstick, and combination of both in comparison to gold standard for detection of Helicobacter pylori (n=143)

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The diagnostic performance of the stool antigen tests was correlated with various demographic, endoscopic, and histologic characteristics of the patients. The one case with discordant results between K-set and dipstick was excluded from the study. Among the 142 patients, 80 were male and 62 were female, with a median age of 40 (range: 16–74 years). The prevalence of H. pylori in males and females was 17.5% and 24.2%, respectively. The prevalence of H. pylori in patients <40 and ≥40 years was 22.5% and 19.7%, respectively. The diagnostic performance of the tests in these subgroups was found to be similar to the overall performance with low sensitivity and high specificity [Table 2].

Table 2: Correlation of diagnostic performance of K-set, dipstick, and combination of both in comparison to gold standard with various demographic, endoscopic, and histological characteristics

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The most common endoscopic characteristics noted in the study were combination of antral gastritis and duodenitis, 70 (49.29%); normal study, 40 (28.1%); and combination of multiple gastric erosions and ulcers, 21 (14.7%). The prevalence of H. pylori in these groups was 22.5%, 20%, and 19%, respectively. The case excluded from analysis was found to have antral gastritis on endoscopy. The tests were found to have a specificity of 96.77% (30/31), sensitivity of 100% (9/9), and accuracy of 97.5% (39/40) in patients with normal findings in endoscopy. The diagnostic performance in other subgroups was similar to the overall performance [Table 2].

Histopathological examination revealed chronic gastritis in 107 (75.35%), lymphoid aggregates in 10 (7%), and intestinal metaplasia in 17 (11.97%) patients. The patient who was excluded from the analysis was found to have the feature of chronic gastritis on histopathological examination. Only one patient had normal finding identified on histology. The prevalence of H. pylori in patients with chronic gastritis, lymphoid aggregates, and intestinal metaplasia was 22.49%, 30%, and 0%, respectively. The correlation of diagnostic performance of the kit with histologic characteristics is shown in [Table 2].

Discussion

This study demonstrated the overall diagnostic performance of the stool ICT with high specificity, positive and negative predictive value, and accuracy and a relatively low sensitivity. The performance of these kits was unaffected by various demographic, endoscopic, and histological characteristics.

Although H. pylori prevalence ranging from 28% to 60% has been reported, in the present study, the prevalence of H. pylori infection was 20.9%.^[12] The relatively lesser prevalence reported in the present study might be due to the inclusion of all patients who underwent endoscopy for the evaluation of various UGI disorders. The choice of an adequate and accurate diagnostic test depends on the predictive accuracy, cost and availability, rapidity of the results, and acceptability to the patients.^[13] None of the diagnostic tests in use fits the criterion to be considered as gold standard, and hence, a combination is often used as the reference method.^[14],[15] Based on our previous reports, we have used a combination of rapid urease test and histology as the gold standard.^{[10],[11],[16]}

Although UBT and serological test have a high sensitivity and specificity of 90%, there is a recent shift in interest toward the SBT methods owing to the noninvasiveness and ease of the procedure with acceptable predictive accuracy reported from different geographical regions.^[14] Unlike UBT, the stool antigen detection does not require prior preparation, sophisticated equipment, or an expert technical assistance. Stool antigen tests can be used not only for diagnosis, also to confirm the eradication and for follow-up endoscopy.^[17],[18] A meta-analysis of the evaluation of stool antigen tests demonstrated a sensitivity of 92.4% and specificity of 91.9% in diagnosing H. pylori infection and sensitivity and specificity of 88.3% and 92%, respectively, in assessing eradication status.^[19] However, studies in the literature have reported a variation in the accuracy of the stool antigen test.

Stool antigen tests include EIA and ICT. EIA stool antigen tests include commercially available kits such as Premier Platinum HpSA kit and IDEIA Hp StAR kit, the performance of which has been evaluated in numerous studies.^[20],[21] Vaira et al. and Odaka et al. showed high sensitivity and specificity for EIA-based tests in adult dyspeptic population.^[22],[23] However, EIA requires specialized equipment and here is a considerable delay in obtaining results as the samples are analyzed in batches. In contrast, ICT can be performed on single sample and was reported to be fast and easy to use when compared to EIA in a report comparing five different stool antigen tests.^[24] In the present study, the results were obtained within 10 min. The speed and simplicity of ICT have made it the preferred point of care test, especially in monitoring eradication and follow-up where repeated testing may be necessary.^{[14],[25],[26]} ICT is more appropriate for developing countries where facilities for EIA are lacking.

The performance of the various stool antigen ICTs was found to vary with the type of the molecule used in the kit. Vaira et al. reported 91.4% sensitivity and 94.8% specificity using polyclonal antibody-based ICT.^[22] However, the general consensus is that monoclonal antibody-based tests have been reported to have a better performance when compared to polyclonal antibody tests.^[27],[28] This ready-to-use test utilized membrane technology with latex microspheres.

The diagnostic performance was similar to the previous report on an ICT-based test (ASAN Easy Test) which demonstrated a sensitivity and specificity of 84.5% and 96.2%, respectively.^[25] Chisholm et al. reported a sensitivity of 87.8% and specificity of 81.4% for the ICT-based test using ImmunoCard STAT HpSA.^[26] In contrast, Li et al. reported a high sensitivity of 92.6%, specificity of 88.5%, and an accuracy of 90.6% for a stool antigen ICT card test.^[20] Results of our study were similar with respect to specificity and predictive value; however, sensitivity was suboptimal by both the methods. Performance of combination of K-set and dipstick method did not give any added advantage. The suboptimal sensitivity reported in the present study may be attributed to the low prevalence of H. pylori in the study population (20%) compared to higher prevalence in the literature (>50%).^{[20],[25],[26]} The difficulty in interpreting the faint bands contributing to the false negatives could have contributed to the low sensitivity. Moreover, the use of only one sample per patient can also lower sensitivity of the test. However, the sensitivity of the tests was relatively lower in the previous reports as well. The accuracy was high (92.95%) and was comparable to the previous reports, thus ensuring its reliability as a tool for detection of H. pylori.

The diagnostic performance of ICT was not significantly affected by age groups or gender. Jekarl et al. conducted a study on 266 patients to evaluate the diagnostic performance of an ICT-based test showed similar results.^[25] The effect of histological or endoscopic diagnosis on the performance of the test was found to be limited though a higher performance was reported in patients with ulcer on endoscopy.^[29] The present study reported optimum sensitivity and high specificity in the various subgroups of endoscopic and histological characteristics. The accuracy of the test was reported to be more than 90% in all the demographic, endoscopic, and histological subgroups, thus making it a reliable diagnostic tool. In patients with a normal study on endoscopy, the test demonstrated high performance with 100% sensitivity and 96% specificity. Hence, these tests may be suitable for a pretreatment diagnosis of H. pylori in the population as well.

It was reported that stool antigen tests can be used as ideal test for follow-up after eradication as, unlike UBT, these were not affected by the use of PPIs.^[30] As follow-up evaluation was not done in the present study, the effect of PPI was not assessed. The performance of the test in the pediatric population was also not assessed as these patients were excluded. The difficulty faced in reading the faint bands can be overcome by the use of a more sensitive indicator.

Conclusions

Stool-based ICT test is rapid and noninvasive diagnostic test with an overall good diagnostic performance. However, owing to the relatively low sensitivity, it should be primarily used as a rapid test for determining eradication. This will obviate the need for repeated cumbersome UBT or invasive endoscopic tests to confirm eradication.

Acknowledgment

The authors acknowledge the Coris BioConcept, Gembloux, Belgium, for provision of the test kits and funding for the study (Pylori-Strip/Pylori K-Set, Corisbio). The authors also would like to thank Dr. Sanjeev Srinivasan and Dr. Anchu Anna Cherian for their contribution to the conduct of the study.

Financial support and sponsorship

This study was financially supported by the Coris BioConcept, Gembloux, Belgium.

Conflicts of interest

There are no conflicts of interest.

References

1.	Kate V, Ananthakrishnan N, Badrinath S, Ratnakar C. Prevalence of Helicobacter pylori infection in disorders of the upper gastrointestinal tract in South India. Natl Med J India 1998;11:5-8.
2.	Lopes AI, Vale FF, Oleastro M. Helicobacter pylori infection – Recent developments in diagnosis. World J Gastroenterol 2014;20:9299-313.
3.	Thijs JC, van Zwet AA, Thijs WJ, Oey HB, Karrenbeld A, Stellaard F, et al. Diagnostic tests for Helicobacter pylori: A prospective evaluation of their accuracy, without selecting a single test as the gold standard. Am J Gastroenterol 1996;91:2125-9.
4.	Antoine C, Lozniewski A, De Korwin JD, Conroy MC, Feldman L, Duprez A, et al. Comparative study of four commercialized serologic methods for the diagnosis of gastric Helicobacter pylori infection. Gastroenterol Clin Biol 1995;19:182-8.
5.	Peeters M. Urea breath test: A diagnostic tool in the management of helicobacter pylori-related gastrointestinal diseases. Acta Gastroenterol Belg 1998;61:332-5.
6.	Tanaka A, Watanabe K, Tokunaga K, Hoshiya S, Imase K, Sugano H, et al. Evaluation of Helicobacter pylori stool antigen test before and after eradication therapy. J Gastroenterol Hepatol 2003;18:732-8.
7.	Gisbert JP, Cabrera Md Mdel M, Pajares JM. Stool antigen test for initial Helicobacter pylori diagnosis and for confirmation of eradication after therapy. Med Clin (Barc) 2002;118:401-4.
8.	Tiryaki Z, Yilmaz-Ciftdoǧan D, Kasirga E. Diagnostic value of stool antigen and antibody tests for Helicobacter pylori infection in Turkish children with upper gastrointestinal complaints before and after eradication. Turk J Pediatr 2010;52:505-11.
9.	Coris-Pylori-Strip. Rapid Diagnostic test for in vitro Detection of Helicobacter Pylori Antigen in Stool Specimens. Available from: http://www.corisbio.com/Products/Human-Field/Helicobacter-pylori.php. Accessed on May 20, 2018
10.	Jones VS, Kate V, Ananthakrishnan N, Badrinath S, Amarnath SK, Ratnakar C. Standardization of urease test for the detectionn of Helicobacter pylori. Indian J Med Microbiol 1997;15;181-3.
11.	Valooran GJ, Kate V, Jagdish S, Basu D. Sequential therapy versus standard triple drug therapy for eradication of Helicobacter pylori in patients with perforated duodenal ulcer following simple closure. Scand J Gastroenterol 2011;46:1045-50.
12.	Eusebi LH, Zagari RM, Bazzoli F. Epidemiology of Helicobacter pylori infection. Helicobacter 2014;19 Suppl 1:1-5.
13.	Patel SK, Pratap CB, Jain AK, Gulati AK, Nath G. Diagnosis of Helicobacter pylori: What should be the gold standard? World J Gastroenterol 2014;20:12847-59.
14.	Vaira D, Ricci C, Menegatti M, Gatta L, Berardi S, Tampieri A, et al. Stool test for Helicobacter pylori. Am J Gastroenterol 2001;96:1935-8.
15.	Monteiro L, de Mascarel A, Sarrasqueta AM, Bergey B, Barberis C, Talby P, et al. Diagnosis of Helicobacter pylori infection: Noninvasive methods compared to invasive methods and evaluation of two new tests. Am J Gastroenterol 2001;96:353-8.
16.	Bose AC, Kate V, Ananthakrishnan N, Parija SC. Helicobacter pylori eradication prevents recurrence after simple closure of perforated duodenal ulcer. J Gastroenterol Hepatol 2007;22:345-8.
17.	Choi J, Kim CH, Kim D, Chung SJ, Song JH, Kang JM, et al. Prospective evaluation of a new stool antigen test for the detection of Helicobacter pylori, in comparison with histology, rapid urease test, (13) C-urea breath test, and serology. J Gastroenterol Hepatol 2011;26:1053-9.
18.	Konstantopoulos N, Rüssmann H, Tasch C, Sauerwald T, Demmelmair H, Autenrieth I, et al. Evaluation of the Helicobacter pylori stool antigen test (HpSA) for detection of helicobacter pylori infection in children. Am J Gastroenterol 2001;96:677-83.
19.	Gisbert JP, de la Morena F, Abraira V. Accuracy of monoclonal stool antigen test for the diagnosis of H. Pylori infection: A systematic review and meta-analysis. Am J Gastroenterol 2006;101:1921-30.
20.	Li YH, Guo H, Zhang PB, Zhao XY, Da SP. Clinical value of helicobacter pylori stool antigen test, immunoCard STAT HpSA, for detecting H pylori infection. World J Gastroenterol 2004;10:913-4.
21.	Aksoy DY, Aybar M, Ozaslan E, Kav T, Engin D, Ercis S, et al. Evaluation of the helicobacter pylori stool antigen test (HpSA) for the detection of Helicobacter pylori infection and comparison with other methods. Hepatogastroenterology 2003;50:1047-9.
22.	Vaira D, Malfertheiner P, Mégraud F, Axon AT, Deltenre M, Hirschl AM, et al. Diagnosis of Helicobacter pylori infection with a new non-invasive antigen-based assay. HpSA European study group. Lancet 1999;354:30-3.
23.	Odaka T, Yamaguchi T, Koyama H, Saisho H, Nomura F. Evaluation of the Helicobacter pylori stool antigen test for monitoring eradication therapy. Am J Gastroenterol 2002;97:594-9.
24.	Korkmaz H, Kesli R, Karabagli P, Terzi Y. Comparison of the diagnostic accuracy of five different stool antigen tests for the diagnosis of Helicobacter pylori infection. Helicobacter 2013;18:384-91.
25.	Jekarl DW, An YJ, Lee S, Lee J, Kim Y, Park YJ, et al. Evaluation of a newly developed rapid stool antigen test using an immunochromatographic assay to detect Helicobacter pylori. Jpn J Infect Dis 2013;66:60-4.
26.	Chisholm SA, Watson CL, Teare EL, Saverymuttu S, Owen RJ. Non-invasive diagnosis of Helicobacter pylori infection in adult dyspeptic patients by stool antigen detection: Does the rapid immunochromatography test provide a reliable alternative to conventional ELISA kits? J Med Microbiol 2004;53:623-7.
27.	Domínguez J, Forné M, Blanco S, Prat C, Galí N, Latorre I, et al. Comparison of a monoclonal with a polyclonal antibody-based enzyme immunoassay stool test in diagnosing Helicobacter pylori infection before and after eradication therapy. Aliment Pharmacol Ther 2006;23:1735-40.
28.	Koletzko S, Konstantopoulos N, Bosman D, Feydt-Schmidt A, van der Ende A, Kalach N, et al. Evaluation of a novel monoclonal enzyme immunoassay for detection of Helicobacter pylori antigen in stool from children. Gut 2003;52:804-6.
29.	Shimoyama T. Stool antigen tests for the management of Helicobacter pylori infection. World J Gastroenterol 2013;19:8188-91.
30.	Kodama M, Murakami K, Okimoto T, Fukuda Y, Shimoyama T, Okuda M, et al. Influence of proton pump inhibitor treatment on Helicobacter pylori stool antigen test. World J Gastroenterol 2012;18:44-8.