The performance of five immunoassays for detection of immunoglobulin G antibody against Helicobacter pylori in 191 dyspeptic patients was evaluated. The sensitivities, specificities, accuracies, positive predictive values, and negative predictive values ranged from 86.32 to 97.89%, 57.95 to 72.22%, 77.02 to 83.76%, 71.54 to 77.42%, and 83.33 to 96.23%, respectively. The immunoglobulin A test kit also gave a high sensitivity and negative predictive value (95.79 and 91.40%, respectively), while the specificity was relatively low (51.14%).Serological assay for Helicobacter pylori antibody is a noninvasive method to detect H. pylori infection. It has been reported to have sensitivity and specificity in predicting the status of H. pylori infection in untreated patients as accurately as invasive tests (11,12). However, it has been suggested that serological tests for H. pylori should be locally validated (7), because assays validated in one region may yield variable diagnostic performances in others. These variations may be attributed to many factors, including the source of antigen used, the prevalence of infection in each population studied, and the reference method used to determine true H. pylori infection status. Therefore, reevaluation is needed before implementing a test in different populations. In Thailand, the seroprevalence of H. pylori infection has been reported to be higher than that in industrialized countries (10), and commercially available enzyme immunoassay (EIA) test kits have been reported to have lower sensitivities and specificities compared to in-house EIAs in Thai dyspeptic patients (1). We therefore evaluated the performance of five commercial test kits for detecting of immunoglobulin G (IgG) A total of 191 patients (57 males and 134 females; age range, 16 to 83 years [mean, 39 years]) were studied. Endoscopy was performed in all patients, and 183 (95.81%) of them were diagnosed as having nonulcer dyspepsia while the remaining 8 patients (4.19%) had a duodenal ulcer. Patients who received antibiotic therapy, bismuth treatment, or a proton pump inhibitor or H 2 blocker within 1 month prior to the study were excluded. Written informed consent was obtained from all patients before the study. Five milliliters of clotted blood was obtained on the day of endoscopy. Sera were kept at Ϫ20°C until analyzed. The biopsy specimens from the antrum and stomach body were obtained for rapid urease (CLO) test and histological and cultural examination. All the tests were performed according to the manufacturer's instructions and without the knowledge of the status of the patient's infection. The results of these examinations were described previously (4).In this study, a patient was considered infected with H. pylori when either culture was positive or both rapid urease (CLO) test and histological analysis were positive.Statistic analyses for sensitivity, specificity, accuracy, positive predictive value, and negative predictive value were calculated against the status of H. pylori infection. As shown in Table...