Pepsinogen I (PGI) is the inactive precursor of pepsin, secreted by gastric chief and mucous neck cells in the fundic glands. Serum PGI levels, particularly the PGI/PGII ratio, are well-established biomarkers for chronic atrophic gastritis and predictors of gastric cancer risk. Reduced PGI concentrations strongly correlate with gastric mucosal atrophy, while restoration is often observed following Helicobacter pylori eradication and mucosal recovery. These characteristics make PGI a valuable noninvasive marker for disease diagnosis, prognosis, and therapeutic monitoring. Catalina’s PGI antibodies deliver high sensitivity and specificity, supporting advanced research in gastroenterology, gastric pathology, and cancer biology.