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Original Articles: Hepatology and Nutrition

Stool Antigen Test for Diagnosis of Helicobacter pylori Infection in Children With Symptomatic Disease: A Prospective Study

Elitsur, Yoram*; Lawrence, Zandra*; Hill, Ivor

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Journal of Pediatric Gastroenterology and Nutrition: July 2004 - Volume 39 - Issue 1 - p 64-67
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Abstract

Helicobacter pylori (Hp) infection can be acquired in childhood and is a major factor in the development of peptic ulcer in children. Early diagnosis and treatment is recommended to reduce morbidity and the potential for malignancy (1–3). The various diagnostic tests for Hp in the pediatric population are less accurate than in adults. As a consequence histologic findings have been considered the best diagnostic tool for infection in children (4,5). Recently, a noninvasive stool test for the detection of Hp antigen was developed (HpSA, Meridian Diagnostics, Cincinnati, OH, U.S.A.). Studies in adults from Europe and the United States demonstrated a high sensitivity and specificity for this test (6–9) and a lower cost than endoscopy (10). The test was approved by the United

States Food and Drug Administration (FDA) as a pre-endoscopic diagnostic test for Hp infection in adults. Depending on the standards used in comparison to fecal antigen (histologic findings or urea breath test) the sensitivity of the HpSA test in children ranges from 73% to 100% (11–17). To date, no such studies have been reported in children from the United States. This study evaluated the accuracy of the HpSA test for the detection of Hp infection in children in the United States.

PATIENTS AND METHODS

Patient Population

Patients were prospectively recruited to the study from two pediatric gastroenterology clinics at Marshall University, Huntington, West Virginia, and Wake Forest University, Winston-Salem, North Carolina. All patients requiring an upper endoscopy were considered for the study. Exclusion criteria were young age (<3 months) and use of antibiotics, bismuth salts, and proton pump inhibitors in the 2 months before endoscopy. Patients with prior Hp infection or inflammatory bowel disease were excluded. The study was approved by the institutional review board of each center, and informed consent was obtained for all subjects enrolled.

Endoscopic Procedure

During endoscopy, the gastric mucosa was evaluated for ulceration or nodularity and results were recorded. Two biopsy specimens from the antrum and two from the corpus were taken for histologic evaluation in every child. One biopsy specimen from the antrum and one from the corpus were also obtained for rapid detection of Hp organisms by urease test (RUT) (CLOtest, Ballard Medical Products, Draper, Utah, U.S.A.). Inflammation was assessed on biopsies stained with hematoxylin and eosin and Hp organisms were detected by Giemsa stain. Pathologic evaluation was performed by the local pathologist in each center. At the time of histologic assessment, the pathologist was blinded to the results of the stool antigen test and the RUT.

Stool Collection and Hp Antigen Determination

A stool specimen was collected by the patient in the 7 days preceding the endoscopic procedure. The sample was placed in a container provided to the patient at enrollment, and kept in the freezer at −20°C until the day of endoscopy. The samples were then kept frozen at −20°C to −70°C at the local institution until analysis.

Testing was performed at both participating sites. Hp antigen was assessed using an enzyme-linked immunosorbent assay (ELISA) kit provided by the manufacturer (Meridian Diagnostics, Cincinnati, OH, U.S.A.). According to the manufacturer's instructions, absorbances were read at both single (450-nm) and dual (450/630-nm) wavelengths. Positive and negative controls were run with each batch of samples. A positive test was indicated by a yellow color, and a negative test was either colorless or faint yellow.

Data Interpretation

Patients were considered “positive” when Hp was identified on by histology and the RUT was positive. Patients were considered “negative” when both histologic testing and RUT were negative. Patients with discordant results were excluded from the final calculation. Stool antigen results were read at wavelengths of 450 nm and 450/630 nm, according to the manufacturer's instructions. Equivocal results were repeated until 2 optical density (OD) readings were concordant. Equivocal values were excluded from the final calculation. Stool antigen test results were compared with histologic and RUT results.

RESULTS

One hundred twenty-one children were recruited between December 2000 and July 2002. There were 64 male and 57 female (ratio 1.1:1.0) patients, with a mean (±SD) age of 10.1 ± 3.7 years (median: 10.0 years; range, 0.5–17 years). The ethnic distribution of the group was 4 African Americans, 1 Hispanic, and 116 Caucasians. Gastric nodularity was found in 18 children and ulceration in 10 (esophageal, 3; gastric, 2; and duodenum, 5). Histologic testing and RUT results were concordant in 115 (95%) children of whom 9 had Hp. Results were discordant in 6 (5%) children (all 6 with positive histology and negative CLOtest). By our definition of a “positive” patient (positive histologic findings and CLOtest), the stool antigen test had a sensitivity and positive predictive value of 67% and 86%, respectively (Table 1). We previously reported a low sensitivity of CLOtest in children (18), so we further analyzed the data using positive histologic findings only as the definition of a “positive” patient. Using this criterion of positivity, the sensitivity of the stool antigen test decreased (sensitivity 47%, Table 1). Because previous reports have suggested that the stool antigen (HpSA) is less accurate in children younger than 5 years (12,19,20), we divided our children into those older and younger than 5 years of age. Using histologic findings for the definition of positive, a higher sensitivity of the stool antigen test (HpSA) was observed in the young age group, but this difference was not statistically significant (P = 0.64, Fisher exact test;Table 2).

TABLE 1
TABLE 1:
The accuracy of stool antigen test (HpSA)*
TABLE 2
TABLE 2:
The effect of age on HpSA results*

DISCUSSION

HpSA is a noninvasive method for determining the presence of Hp organisms. Because it is noninvasive, it is attractive for physicians who care for children. Studies in adults using histologic criteria as proof of positivity have found HpSA is a sensitive diagnostic tool (7–9,21), and a good measure of response to therapy (7,21). In our study, we found the sensitivity of HpSA to be 67% with a PPV of 86%. These figures are within the lower range of sensitivities reported in children from other countries (11–14,17). When the definition of infection was changed to positive histologic findings only, the sensitivity and PPV of HpSA decreased substantially (Table 1). These results are below an acceptable level to confirm the presence of Hp infection in children. Accordingly, histologic findings should remain the standard for the diagnosis of Hp infection in children.

It has been suggested that the sensitivity of HpSA may be lower in children younger than 5 years and that caution should be exercised in interpreting test results. The reasons for the lower accuracy rate of the stool antigen test in children are not known (12,19,20). In our study, the sensitivity of the test in children less than 5 years was higher than in older children (100%v 38%, respectively), but this difference did not reach statistical significance, probably because of the small number of positive patients in the younger group. A larger number of young children must be studied to clarify this issue. It is possible that cross reactivity of the HpSA (a polyclonal antigen test) with nonviable or coccoid forms of the Hp bacterium may produce false-positive results (22,23). If true, this could limit the utility of the test especially for monitoring children after therapy.

To improve the accuracy of the stool antigen test, a monoclonal antibody has been developed and preliminary results in adults and children are promising (24,25). Comparisons between the tests (monoclonal and polyclonal) in children have shown that the monoclonal antibody has a higher sensitivity than the polyclonal antibody (98%v 93.8%). More important, the separation in OD values between positive and negative results is better with the monoclonal antibody (26). If these results are confirmed in future studies, the monoclonal antibody test may prove to be a useful, noninvasive method for diagnosing Hp infection in children.

In summary, this is the first study to evaluate the accuracy of stool antigen for the detection of Hp infection in children in the United States. Our results are comparable to those reported elsewhere in children and demonstrate that the commercial polyclonal HpSA test cannot replace histologic findings as the best standard for the diagnosis of Hp infection in children.

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Keywords:

Children; H. pylori; Stool antigen

© 2004 Lippincott Williams & Wilkins, Inc.