Immune responses to Helicobacter pylori in children with recurrent abdominal pain.

The systemic immune response to Helicobacter pylori was examined in 69 children with recurrent abdominal pain and upper gastrointestinal symptoms. Twenty one (30%) children were histologically positive for H pylori. Eighteen of the 21 positive subjects and two H pylori negative subjects (one with normal mucosa, one with lymphocytic gastritis) were positive for H pylori IgG antibodies by enzyme linked immunosorbent assay (ELISA) (86% sensitivity, 98% specificity). In children with H pylori associated gastritis, there was a significant positive correlation (p less than 0.05) between IgG antibody titres and patient age. Intra-assay comparison of sera from histologically negative adults with those of histologically negative children showed that the cut off for positivity in the ELISA for adults was greater than that for children. Immunoblotting showed IgG positivity in 20 of the 21 patients with H pylori infection (95% sensitivity). Both ELISA and immunoblotting for IgA and IgM H pylori antibodies had poor discriminatory value for determining infection. Serological detection of H pylori IgG antibodies seems to be valuable in the assessment of children presenting with recurrent abdominal pain and other gastrointestinal symptoms, but assays must first be validated in paediatric populations.     

Immunoglobulin G antibody against Helicobacter pylori: clinical implications of levels found in serum

The clinical significance of high levels of antibody against Helicobacter pylori is still unclear. We sought to evaluate whether the serum antibody levels could predict the presence of macroscopic gastroduodenal disease, to identify factors that correlate with antibody levels in a multivariate context, and to determine the predictive value of antibody levels for diagnosing H. pylori infection. The grades of gastritis and density of H. pylori colonization were scored separately using the updated Sydney system for antral and body mucosa. An enzyme-linked immunosorbent assay (ELISA) for the quantitative detection in serum of IgG antibodies to H. pylori was performed. Of the 170 dyspeptic patients, 105 (62%) had H. pylori infection. There was no difference in antibody levels among endoscopic findings of normal mucosa, chronic gastritis, and duodenal ulcer. On multivariate linear regression analysis, the status of H. pylori infection, mononuclear cell infiltration of body mucosa, and age correlated with antibody levels. The negative predictive value for antibody levels of <30 U/ml is 94%, and the positive predictive value of antibody levels of >70 U/ml is 98%. We conclude that serum antibody levels do not predict the severity of gastroduodenal diseases or the density of H. pylori colonization in H. pylori-infected dyspeptic patients. Higher levels are associated with the presence of H. pylori infection, the chronic gastritis score of the corpus, and older age. Setting a gray zone is necessary for ELISA, since the accuracy in this zone does not allow a precise determination of H. pylori status.     

Serological detection of Helicobacter pylori by a flow microsphere immunofluorescence assay.

A flow cytometric immunofluorescence assay (FMIA) for the detection of immunoglobulin G antibodies to Helicobacter pylori was developed. A multicomponent antigen was prepared and used to coat carboxylated polystyrene microspheres for reaction with patient sera followed by fluorescein isothiocyanate-labelled goat anti-human immunoglobulin G. The reacted microspheres were collected with a flow cytometer, and fluorescence was quantitated relative to the cutoff value provided by pooled sera from patients in whom H. pylori could not be demonstrated by culture or histology. Serum samples from 28 H. pylori-positive patients and 27 H. pylori-negative patients were tested by FMIA. Additionally, an in-house enzyme-linked immunosorbent assay (ELISA) employing the same antigen preparation and a commercially available ELISA were used to assay the patient population. Both the FMIA and in-house ELISA were 100% sensitive and 89% specific with positive and negative predictive values of 90 and 100% and no equivocal results. The commercial ELISA was 96% sensitive and 89% specific with positive and negative predictive values of 90 and 96% and five equivocal results. FMIA provides a rapid, inexpensive, and easily performed means for serodiagnosis of H. pylori.     

Isolation and preliminary evaluation of a low-molecular-mass antigen preparation for improved detection of Helicobacter pylori immunoglobulin G antibodies.

Previously, immunoglobulin G (IgG) antibodies to five antigens with a relative molecular mass of between 15 and 30 kDa from Helicobacter pylori were found to be significantly more frequent in H. pylori-infected patients than in noninfected patients. In this study, these specific low-molecular-mass (LMW) antigens were separated by ultrafiltration of whole-cell sonicates. The LMW antigen preparation was evaluated by enzyme-linked immunosorbent assay with serum samples from 76 children with abdominal symptoms and 151 adults with dyspeptic symptoms. H. pylori was cultured or seen in 40 (53%) children and 83 (55%) adults. Increased antibody levels to H. pylori were found in serum from 35 (46%) children and 88 (58%) adults. Values for sensitivity, specificity, and predictive value of positive and negative results of the test were higher with LMW antigens than with the heat-stable antigen previously described. The low specificity and predictive value of a positive result were due to seropositive results for 21 persons with a negative culture for H. pylori and negative microscopy results for Helicobacter-like organisms in biopsies from gastric mucosa. Histologically, chronic gastritis was demonstrated in 43% of these persons, and 19% had peptic ulcer, indicating that they have or have had H. pylori infection. Specific antibodies to H. pylori were confirmed in all 21 patients by the Western immunoblot technique. Use of the LMW antigen improved the IgG antibody detection in patients with H. pylori infection, even though the results reflect the difficulties in establishing a true gold standard for diagnosis of H. pylori infection.     

Evaluation of the performance of commercial test kits for detection of Helicobacter pylori antibodies in serum.

We have compared the sensitivities, specificities, and predictive values of three commercial serological assays for the diagnosis of Helicobacter pylori infection. A qualitative latex method (Pyloriset; Orion Diagnostics), a semiquantitative enzyme-linked immunosorbent assay (ELISA) (GAP test IgG; Bio-Rad), and a quantiative ELISA (Helico-G; Porton Cambridge) were used in 109 untreated dyspeptic patients. The presence of H. pylori was established when the results of culture and/or histology of the gastric biopsies taken were positive. The prevalence of H. pylori infection was 62% (52% in 42 patients younger than 45 years of age and 69% in 67 patients older than 45 years of age). Sensitivities and specificities were 68 and 76% for Pyloriset, 89 and 77% for GAP test IgG, and 82 and 83% for Helico-G. The positive predictive values for all three tests were between 85 and 90%. The predictive values for the absence of disease with a negative result were 62, 82, and 74% for Pyloriset, the GAP test, and Helico-G, respectively. With Helico-G in the younger group (less than 45 years), sensitivity significantly lower (71 versus 87%) and a positive predictive value lower than those for the older group (greater than 45 years) were found. Either the sensitivities and specificities of commercial methods for the measurement of antibodies to H. pylori in serum must be improved or the relationship between the presence of antibodies and the presence of bacteria in the stomach at the time of investigation is too weak to allow the use of serological techniques instead of culture and histological investigation of gastric biopsy material.     

Correlation of serum antibody titres with invasive methods for rapid detection of Helicobacter pylori infections in symptomatic children

Helicobacter pylori (H. pylori) is causally associated with peptic ulcer disease and gastric carcinoma. Typically, children get infected during the first decade of life, but diseases associated with H. pylori are seen mainly in adults. Multiple diagnostic methods are available for the detection of H. pylori infection. The aim of this study was to evaluate the correlation and diagnostic accuracy of three invasive methods [rapid urease test (RUT), histology and bacterial culture] and one non-invasive method (IgG serology) for diagnosis of H. pylori infection in a prospective cohort study conducted on 50 symptomatic children between two and eighteen years of age. Endoscopies with gastric biopsies were performed for RUT, culture and histopathological examination, respectively. IgG antibodies were measured in patient sera using a commercially available enzyme-linked immunosorbent assay (ELISA). RUT and positive H. pylori IgG antibodies were concordant in 88% (44/50) of patients. Both tests were negative in 32% (16/50), and both were positive in 56% (28/50). Disagreement occurred in 12% (6/50) of the patients: three of them (6%) had positive RUT and negative H. pylori IgG, and another three (6%) had negative RUT and positive H. pylori IgG. A combination of RUT with non-invasive serology constituted the optimum approach to the diagnosis of H. pylori infection in symptomatic children. The non-invasive serological test (ELISA) could not be used alone as the gold standard because it cannot distinguish between active and recently treated infection; and bacterial culture could not be used alone because of its low sensitivity.     

A practical single sample dry latex agglutination test for Helicobacter pylori antibody detection.

Assessment of a single serum sample for Helicobacter pylori antibodies is frequently requested in routine diagnostic laboratories. Current enzyme linked immunosorbent assay (ELISA) kits are not ideal for testing small numbers of serum samples and some have low sensitivities, specificities or large grey zones. A panel of 90 serum samples from patients who had presented for routine upper endoscopy was used to compare three kits for the detection of H pylori antibodies: (1) Pyloriset Dry, total antibody latex agglutination, Orion Diagnostica, Espoo, Finland; (2) Pyloriset enzyme immunoassay (EIA), IgG ELISA, Orion; and (3) Hel-p, IgG ELISA, Amrad, Kew, Victoria, Australia. Diagnosis of H pylori positivity was made if culture results and either rapid urease test or histopathology were positive. The sensitivity, specificity, positive, and negative predictive value for each test was as follows: Orion: latex 93.3%, 95.6%, 95.5%, 93.3%, respectively; Orion: EIA-G 84.4%, 97.8%, 97.4%, 84.4%, respectively; and Amrad: EIA-G 100%, 88.9%, 90%, 100%, respectively. The latex test performed better than the EIAs with respect to sensitivity and specificity.     

Serological detection of Helicobacter pylori antibodies in children and their parents.

The antibody response to Helicobacter pylori was examined in 56 children (ages 5 to 18) to determine whether serological tests can be used for diagnosis. Twenty-four children (43%) were H. pylori positive and 32 children (57%) were H. pylori negative by culture and histological examination of endoscopic biopsy specimens. The immune response was also examined in 39 nonendoscoped parents of the children. H. pylori-specific immunoglobulin G (IgG) and IgA antibodies were detected by the flow microsphere immunofluorescent assay (FMIA). IgG was also detected by using the Pyloristat enzyme-linked immunosorbent assay (ELISA). The sensitivity, specificity, and positive and negative predictive values for the FMIA for IgG were 100, 97, 96, and 100%, respectively. The respective values for the Pyloristat ELISA for IgG were 96, 94, 92, and 97%. The respective values for the FMIA for IgA were 50, 100, 100, and 73%. Both assays identified the same 19 parents as IgG positive, while FMIA identified 17 of the 19 parents as IgA positive.     

Salivary immunoglobulin G assay to diagnose Helicobacter pylori infection in children.

An in-house enzyme-linked immunosorbent assay (ELISA) for measurement of Helicobacter pylori-specific immunoglobulin G (IgG) and IgA in saliva was evaluated by comparison with histopathologic (Giemsa staining) and biochemical (urease quick test) examination of gastric biopsy specimens obtained from 112 children referred for diagnostic gastroscopy. Serum H. pylori IgG was also measured in a subgroup of 50 children by the same ELISA. Salivary H. pylori IgG levels were significantly higher in H. pylori-positive (n = 57) than in H. pylori-negative (n = 55) children (P < 0.001). The sensitivity and specificity of the salivary IgG test were 93 and 82%, respectively; the positive and negative predictive values were 84 and 92%, respectively; and the accuracy was 87.5%. Salivary H. pylori IgA did not distinguish H. pylori-positive from H. pylori-negative children. The performance of serum H. pylori IgG was slightly (3 to 6%) better than that of salivary H. pylori IgG. The salivary IgG test can be considered a useful tool for the screening of H. pylori infection in children.     

Oral fluid antibody detection in the diagnosis of Helicobacter pylori infection.

The aim of this study was to evaluate an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-Helicobacter pylori specific IgG antibodies in specimens of oral fluid. Antral biopsy specimens, serum and oral fluid samples were collected from 81 patients attending for upper gastrointestinal endoscopy. The presence or absence of current H. pylori infection was determined by culture, histology and urease detection. Anti-H. Pylori specific IgG was detected in serum by an established in-house ELISA and in oral fluid by an ELISA developed for this study. In all, 34 (42%) of 81 patients were positive for H. pylori by one or more of the 'gold standard' tests (culture, histology and urease detection). The oral fluid ELISA had a sensitivity of 94% and specificity of 85% with regard to current H. pylori infection. The serum ELISA had a sensitivity and specificity of 91%. There was an overall agreement of 88% between serum and oral fluid antibody detection. The detection of anti-H. pylori specific IgG in oral fluid by ELISA is comparable in sensitivity and specificity with serum-based methods. Oral fluid-based ELISA could provide a reliable, non-invasive method for the diagnosis of H. pylori infection, and may be of particular benefit for population surveys.     

Diagnosis of Helicobacter pylori infection by using pyloriset EIA-G and EIA-A for detection of serum immunoglobulin G (IgG) and IgA antibodies.

We evaluated the performance of new enzyme immunoassay (EIA) kits (Pyloriset; Orion Corporation, Orion Diagnostica, Espoo, Finland) for the detection of immunoglobulin G (IgG) and IgA antibodies to Helicobacter pylori in serum. Serum samples from 195 patients with upper abdominal complaints were collected. Biopsy specimens of the gastric mucosae were taken for histological analysis and bacterial culture. The sensitivity, specificity, and positive and negative predictive values, and efficacy of the Pyloriset EIA-G in detecting IgG antibodies to H. pylori were 92, 84, 88, 90, and 89%, respectively, when compared with those of the reference methods used. The corresponding data for detection of IgA antibodies were 80, 89, 89, 79, and 84%, respectively. The overall prevalence of defined H. pylori positivity was 54%. Moreover, the antibody tests showed a very good correlation with the biopsy findings. IgG antibodies were found in 93% of sera from patients with documented gastritis and H. pylori positivity, whereas only 4% of the sera from patients with documented gastritis and H. pylori-negative patients was positive. The results obtained for IgA antibodies were 81 and 6%, respectively. We conclude that the Pyloriset EIA-G, the test for IgG antibodies, is a good and reliable test for the detection of antibodies to H. pylori and as an indication of H. pylori infection. The determination of IgA antibodies may be used as a test that complements the IgG antibody assay.     

Use of serum-specific immunoglobulins A and G for detection of Helicobacter pylori infection in patients with chronic gastritis by immunoblot analysis.

Multiple invasive and noninvasive tests for detecting Helicobacter pylori infection are available. The current "gold standard" for the diagnosis of H. pylori infection requires histology and the rapid urease test. Our aim was to test the performance of immunoglobulin A (IgA) and IgG immunoblot assays in comparison with that of the gold standard tests for the diagnosis of H. pylori infection. Ninety patients who underwent gastroscopy were analyzed in a prospective study. Fifty-nine of them were defined to be H. pylori positive by the gold standard tests. The IgA and IgG immunoblot assays correctly identified H. pylori infection in 17 and 58 of these patients, respectively, indicating that determination of IgA antibodies seems to be of low diagnostic value for H. pylori infection. In contrast, the sensitivity and specificity of the IgG immunoblot assay were 98 and 71%, respectively, with positive and negative predictive values of 87 and 96%, respectively. Therefore, the IgG immunoblot assay proved to be a sensitive and useful, noninvasive test for the diagnosis of H. pylori infection.     

Diagnostic value of detection of IgM antibodies to Helicobacter pylori.

This report describes the diagnostic value of anti-Helicobacter pylori IgM detection. Serum samples from 9043 symptomatic and asymptomatic individuals were evaluated with ELISA for the presence of anti-H. pylori IgG, IgM, and IgA. The specificity of detected IgM was confirmed by inhibition and cross-reactivity assays. Treatment of IgM-positive specimens with 1% 2-mercaptoethanol resulted in approximately 90% inhibition. Our data suggest a low level of cross-reactivity (5%) between H. pylori and four different enteropathogenic bacteria tested. The specificity of anti-H. pylori IgM was also demonstrated by Western blot and linearity studies. Data show that the detected IgM is highly specific. Western blot analysis revealed a variable IgM response to H. pylori antigens among patients, with the most reactive antigenic fractions being in the range of 55- to 100-kDa. Overall, the data confirm the diagnostic value of anti-H. pylori IgM detection. The prevalence of IgM antibodies to H. pylori in tested sera was significantly higher in symptomatic patients (10.4%) than in asymptomatic individuals (1.1%). Likewise, the percentage of sera positive for IgM alone was higher in symptomatic than in asymptomatic groups (3.8 vs 0.22%). About 5% of sera were positive only for IgA. We concluded that ELISA can be used for the detection of specific IgM to H. pylori and that the presence or absence of IgM antibodies to H. pylori may reflect whether or not an acute infection exists.     

Detection of IgA and low-avidity IgG antibodies for the diagnosis of recent active toxoplasmosis

Objective: To determine the clinical value of testing IgA and the avidity of IgG (by two commercial systems) for the detection of recent active toxoplasmosis (RAT), and to study the IgG avidity during the course of infection.
Methods: The IgA was tested by a capture ELISA (Pasteur, France) and the avidity of IgG was determined by two modified commercial indirect ELISA methods (Sorin, Italy; Behringwerke, Germany) in 12 patients who were not immunosuppressed (group I) and 57 healthy subjects with a past infection by Toxoplasma gondii (group II).
Results: IgA was present in 75% of patients from group I and 21% of subjects from group II. The reliability for diagnosis of RAT was: sensitivity 75%, specificity 84%, positive predictive value 52.9% and negative predictive value 93.3%. In group I, 91.7% of patients had more than 50% low-avidity IgG, by both methods; in group II, 21% of subjects had low-avidity IgG at levels from 40% to 50%, by both methods. The diagnostic reliability of the two methods for the detection of low-avidity IgG in the first samples of RAT was similar when a breakpoint of 50% was used, with values of: sensitivity 91.7%, specificity 100%, positive predictive value 100% and negative predictive value 98%.
Conclusions: The study of IgA is not on its own adequate for diagnosis of RAT. However, testing the avidity of IgG is more reliable for the diagnosis of RAT, in studies of one serum sample or sequential samples.     

Diagnosis of Helicobacter pylori infection by specific gastric mucosal IgA and IgG pylori antibodies.

AIMS--To investigate the diagnostic value of mucosal IgA and IgG Helicobacter pylori antibodies. METHODS--The study population comprised 209 consecutive patients with severe dyspeptic complaints referred for upper gastrointestinal endoscopy. A positive culture or histological identification of H pylori in gastric biopsy specimens, or both, were used to confirm infection. Specific IgA and IgG H pylori antibodies were determined using a modified ELISA technique. RESULTS--Of the 209 patients, 137 were infected with H pylori. The diagnostic value of systemic IgA and IgG H pylori antibodies was confirmed. Systemic IgA antibodies had a sensitivity of 76.6% (95% confidence interval 69.5-83.7) and a specificity of 94.4% (89.1-99.7). The sensitivity and specificity for systemic IgG antibodies were, respectively, 97.1% (94.3-99.9) and 98.6% (95.9-100). A moderate but clinically important correlation was found between local and systemic IgA and IgG. Mucosal IgA H pylori antibodies had a sensitivity of 98.5% (96.5-100) and a specificity of 91.7% (85.3-98.1), while for IgG these figures were, respectively, 88.3% (82.9-93.7) and 98.6% (95.9-100). As a diagnostic test mucosal IgA H pylori antibodies were comparable with culture and histology. CONCLUSION--Determination of local IgA and IgG H pylori antibody levels is a highly sensitive and specific test for the diagnosis of H pylori infection.     

Evaluation of infection by Helicobacter pylori in HIV positive patients trough enzyme immunoassay and specific amplification of DNA

The objective of this work was to assess the effectiveness of detection of specific antibodies anti-Helicobacter pylori (H. pylori) by ELISA and amplification of specific DNA by polimerase chain reaction (PCR) as diagnostic methods of infection of H. pylori in HIV positive patients. Twenty two patients with HIV infection were studied, with ages between 26 to 35 years, 17 masculine, 55% with gastrointestinal symptoms, controlled in the Unit of Immunology, CHET. Inclusion approaches: older than 18 years, with confirmed diagnosis of HIV infection (ELISA and WB), lymphocyte subpopulation and good general conditions. Consent in writing was obtained. Exclusion approaches: previous diagnosis of H. pylori infection or treatment with antibiotics in the three previous months to their inclusion. The quantification of IgG anti H. pylori was carried out by Enzyme Immunoassay methods (ELISA). Biopsy of gastric mucosa was obtained by superior endoscopic study. The amplification of DNA for H. pylori was performed by PCR (Wizard SV Genomik and PCR Ready-Promega). In the statistical analysis was used the test of Fisher, with a level of significance of 5% (0.05). In 15 patients of the total group, antibodies anti H. pylori were confirmed, without statistical association with the presence or not of digestives symptoms, neither with the number of lymphocytes CD4 + in peripheral blood. Also 15 patients were positives by PCR for H. pylori DNA, 73.3% of them presented levels of CD4+ above 200 cells. There was not statistical association between the positivity of this method and levels of lymphocytes CD4+. In 12 of the 15 patients with positive results by PCR, antibodies anti H. pylori were evidenced, and among the 7 patients with negative serology to H. pylori, PCR was positive in three of them. In conclusion, serology is an effective method for the diagnose of H. pylori infection in VIH+ patients, but its negativity doesn't discard the infection for this bacillus.     

Serologic Diagnosis of Helicobacter pylori Infection in Outpatients Aged 45 Years or Less

The diagnostic accuracy of serological tests for Helicobacter pylori was studied in 145 consecutive outpatients aged 45 years or less referred for gastroscopy. Helicobacter pylori infection can be detected by serological tests, including rapid whole-blood tests. The low prevalence of the disease in young people may have a negative effect on the positive predictive value of a test. In this study, the presence of Helicobacter pylori was assessed by a biopsy urease test and histological examination, and by several serological tests: a rapid whole-blood test on fingerstick blood, a latex agglutination serum test, a commercial enzyme immunoassay (EIA) test, and an in-house EIA for detection of antibodies of both the IgG and IgA classes. Helicobacter pylori infection was diagnosed with invasive tests in 21 (14.5%) patients. The sensitivity, specificity, and positive and negative predictive values of the EIA-based tests, compared to histological examination, were 100%, 96-97%, 81-84%, and 100%, respectively. The positive predictive value of the latex agglutination test was 78%, whereas it was only 47% for the whole-blood rapid test used. Although the results of the whole-blood rapid test were unsatisfactory, the quantitative EIA-based tests could reliably detect Helicobacter pylori among young patients, in whom the prevalence of the infection is low.     

Role of ELISA in H. pylori detection and its correlation with urease test

Helicobacter pylori is one of the most common chronic bacterial infection in humans linked to acid peptic diseases, gastric carcinomas and lymphomas. The bacilli produces large amounts of urease and this property has formed the basis of detection of H. pylori by the Christensen's urease test. Where endoscopy is not clinically indicated, serology may be used to establish the diagnosis. This study was undertaken to diagnose H. pylori with the help of Christensen's urease test on endoscopic biopsy specimens & correlated with the detection in Sera, of IgG antibodies against H. pylori, by ELISA technique. The study was conducted on 100 patients suffering from acid peptic disorders out of which 40 (40%) tested positive for H. pylori both by urease and serology. Christensen's urease and ELISA were found to have sensitivities of 85.7% & 90.9% and specificities of 96% and 87.5% respectively. Christensen's urease was taken as a standard method of diagnosis and its correlation with ELISA worked out to (+1) which meant there was a strong positive association between both the tests. Hence either test could be used for primary diagnosis of H. pylori instead of histopathological study and/or culture of H. pylori.     

Antibody to cytotoxin in infection by Helicobacter pylori.

Gastrointestinal disease and colonization by Helicobacter pylori were determined in 36 asymptomatic volunteers and 30 symptomatic individuals undergoing endoscopy and biopsy. Serum antibody immunoglobulin G (IgG) and IgA to H. pylori were measured by enzyme-linked immunosorbent assay. Serum antibody to a cytotoxin produced by H. pylori was detected with a neutralization assay. Serum IgG was 95% predictive of infection by H. pylori, and serum IgA was 88% predictive. Antibody to the cytotoxin was detected in 12 of 18 infected individuals. Antibody to the cytotoxin was a highly specific (96%), but not a very sensitive (67%), indicator of infection by H. pylori. The neutralization assay was 87% predictive of infection. These data confirm the diagnostic value of serum antibody to H. pylori for the detection of infection. The toxin-neutralizing activity of sera from individuals infected with H. pylori suggests that the cytotoxin is produced in vivo. It may therefore contribute to disease associated with H. pylori.     

Use of a novel enzyme immunoassay based on detection of circulating antigen in serum for diagnosis of Helicobacter pylori infection

Recently, noninvasive diagnostic tests for Helicobacter pylori infection have gained in significance. We have developed a sensitive and specific noninvasive immunoassay based on the detection of an H. pylori circulating antigen (HpCA) in sera from H. pylori-infected individuals. Monospecific antibody and Western blot analyses were used to demonstrate the presence of the target antigen in H. pylori cell lysate and serum samples. A novel enzyme-linked immunosorbent assay (ELISA) was developed for the detection of HpCA in serum. Endoscopic biopsy specimens from the gastric antra of 221 individuals (143 males and 78 females) with dyspeptic symptoms were evaluated for H. pylori infection, with culture used as a "gold standard" for diagnosis. The target H. pylori antigen was identified at 58 kDa. HpCA has been detected by ELISA with high degrees of sensitivity, specificity, and efficiency (>90%), and ELISA results show no significant difference (P > 0.05) from results of H. pylori culture of gastric biopsy specimens. The test's positive and negative predictive values were also high (95 and 86%, respectively). In conclusion, a sensitive and specific immunoassay was developed for the detection of HpCA in human serum. This test can be applied for noninvasive laboratory and field diagnoses of H. pylori infection.