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Background: Due to lower operational costs, health maintenance organizations (HMOs) may prioritize Helicobacter pylori stool antigen testing (HpStAg) for the non-invasive diagnosis of H. pylori infection over 13C-urea breath tests (13C-UBTs). The aim of our study was to compare the accuracy of the diagnostic tests for H. pylori. Methods: We performed histology, rapid urease test (RUT), 13C-UBT and HpStAg on consecutive patients referred for gastroscopy. Monoclonal stool antigen test was performed using the LIAISON Meridian chemiluminescent immunoassay. Histology was examined with hematoxylin and eosin, and additional stains were performed at the pathologist’s discretion. For the assessment of 13C-UBT, we compared concordant histology and RUT. HpStAg was compared to the concordant results of two of the three remaining tests. Results: 103 patients were included (36 males (35.0%), age 50.1 ± 18.4 years). The indication for gastroscopy was dyspepsia in 63 (61.2%). Agreement between RUT and histology was 95.9%. For 13C-UBT and HpStAg, respectively, H. pylori positivity was 30% (30/100) and 27.16% (22/81); sensitivity was 97% and 70%; specificity was 100% and 94.4%; accuracy was 98% and 86%; positive predictive value (PPV) was 100% and 86.4%; negative predictive value (NPV) was 93% and 86%. No demographic, clinical, or endoscopic predictors of HpStAg accuracy were identified using logistic regression. Conclusions: 13C-UBT performs better than HpStAg at our institution. When interpreting results, clinicians should consider test limitations.

Intestinal metaplasia (IM) is an intermediate step in the progression from premalignant to malignant stages of gastric cancer (GC). The Popeye domain containing (POPDC) gene family encodes three transmembrane proteins, POPDC1, POPDC2, and POPDC3, initially described in muscles and later in epithelial and other cells, where they function in cell–cell interaction, and cell migration. POPDC1 and POPDC3 downregulation was described in several tumors, including colon and gastric cancers. We questioned whether IM-to-GC transition involves POPDC gene dysregulation. Gastric endoscopic biopsies of normal, IM, and GC patients were examined for expression levels of POPDC1-3 and several suggested IM biomarkers, using immunohistochemistry and qPCR. Immunostaining indicated lower POPDC1 and POPDC3 labeling in IM compared with normal tissues. Significantly lower POPDC1 and POPDC3 mRNA levels were measured in IM and GC biopsies and in GC-derived cell lines. The reduction in focal IM was smaller than in extensive IM that resembled GC tissues. POPDC1 and POPDC3 transcript levels were highly correlated with each other and inversely correlated with LGR5, OLFM4, CDX2, and several mucin transcripts. The association of POPDC1 and POPDC3 downregulation with IM-to-GC transition implicates a role in tumor suppression and highlights them as potential biomarkers for GC progression and prospective treatment targets.