Backgrounds/Aims: In the ABC method, which is a method for risk stratification of gastric cancer using serum anti-Helicobacter pylori antibody and pepsinogen (PG) test, subjects with normal PG and seronegative for H. pylori are named as "Group A" and are regarded as having a low risk of gastric cancer. These "Group A" subjects include unintentionally eradicated cases at relatively high risk, and this study aimed to identify these subjects. Methods: Of the 109 subjects, 76 were classified as uninfected Group A subjects with negative histologic H. pylori infection and no histologic and endoscopic atrophy, and 33 subjects were classified serologically as Group A after successful eradication, which are serologically equal to the unintendedly eradicated cases in Group A. The usefulness of measuring PG levels to detect post-eradication cases was validated by using a receiver operating characteristic (ROC) curve analysis. Results: The area under the ROC curve for PGI level was 0.736 ± 0.06 (p < 0.01; cutoff value, 37.0 ng/mL; sensitivity, 77.6%; specificity, 72.7%), and that for the PGI/II ratio was 0.660 ± 0.06 (p < 0.01; cutoff value, 5.1; sensitivity, 84.2%; specificity, 43.4%). Conclusion: PGI levels of ≤37 ng/mL and PGI/II ratios of ≤5.1 effectively identified unintendedly eradicated cases in Group A.
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