Selection of Lower Cutoff Point of [13C]Urea Breath Test Is Helpful to Monitor H. pylori Eradication After Proton Pump Inhibitor-Based Triple Therapy

Our objectives were to test the efficacy of [¹³C] urea breath test (UBT) for H. pylori infection in patients before and after proton pump inhibitor (PPI) based triple therapy, and thus to trace the optimal cutoff value of UBT to monitor H. pylori eradication; and to analyze the histologic bacterial density and distribution of H. pylori in patients with equivocal UBT. A total of 441 dyspeptic cases patients enrolled and completed the study design, including 120 noninfected and 321 H. pylori-infected patients. All 441 cases had received the same protocol of UBT, in which the baseline and 15-min gas samples after ingestion of 100 mg ¹³C-labeled urea were analyzed for excess ¹³CO₂/¹²CO₂ ratio (ECR). In addition, a first endoscopy was performed in each patient to evaluate the initial status of H. pylori by culture and histology. Of the 321 H. pylori-infected patients, 286 received a second endoscopy and a second UBT six weeks after completing any one of four regimens of the PPI-based triple therapy to document the success of H. pylori eradication. During both sessions of endoscopy, topographic gastric biopsies for histology were sampled to evaluate the distribution and density of H. pylori. Based on the diagnostic standard by culture and histology, the sensitivity and specificity of the first UBT achieved most optimally was 97.5% and 96.7%, respectively, by setting the cutoff point of ECR at 4.0. In contrast, using the same cutoff point of 4.0, the sensitivity and specificity of the second UBT in patients after therapy achieved just 80% and 97.6%, respectively. By applying cutoff points downward of 4.0, 3.5, 3, and 2.5 for the second UBT, the sensitivity was elevated to 80%, 82.8%, 88.6%, and 94.3%, respectively, while the specificity was preserved at more than 95.2%. The overall eradication rate of H. pylori was 87.8% (251/286). Seven of 35 patients with failure of therapy had equivocal ECR at the second UBT (range 2–5), and this accounted for the false negative result. All seven patients had low bacterial densities, and three patients had bacteria distributed only in high body near the cardia. In conclusion, selection of a lower cutoff value of ECR at 2.5 is helpful to maintain the diagnostic accuracy of UBT for monitoring the H. pylori eradication. The equivocal ECR of UBT after therapy would be related to the low bacterial load and its distribution.