24-hour pH monitoring: NERD patients can be classified into different subtypes, and 24-hour pH monitoring can evaluate the effect of GERD patients before and after treatment. The results of 24-hour pH monitoring in patients with reflux esophagitis, Barrett’s esophagus and NERD were found to be significantly different. The results of 24-hour pH monitoring were found to be significantly different. The clinical symptoms and treatment effects were different among the subtypes. The length of Barrett’s mucosa has been shown to correlate with the duration of acid exposure in patients: patients with long segmented Barrett’s esophagus had significantly longer acid exposure than patients with short segmented Barrett’s esophagus. Prolonged exposure of the distal esophageal mucosa to gastric contents induced the development of Barrett’s esophagus, and the significant increase in acid and bile exposure in patients with Barrett’s esophagus disappeared with PPI treatment. Gastric acid and duodenal contents may be necessary to trigger Barrett’s mucosa. Studies have shown that bile reflux without acid is not sufficient to damage the esophageal mucosa. Clinical staging For decades, GERD has been considered a progressive disease. Mild GERD presents with typical reflux symptoms without esophageal mucosal breakdown, and as the disease progresses, reflux esophagitis (from mild to severe) develops, with complications including esophageal stricture, Barrett’s esophagus and esophageal adenocarcinoma as the disease continues to worsen. However, more and more recent studies have shown that NERD is not a mild stage of GERD, and that the degree, frequency and quality of life of patients with NERD are similar to those of patients with GERD. The effectiveness of anti-reflux treatment is also similar. However, NERD patients have a lower outcome for PPI treatment than patients with reflux esophagitis by more than 30%. Several retrospective studies have also shown that few patients with NERD progress to reflux esophagitis or Barrett’s esophagus in the natural course of their disease, and most patients with NERD remain NERD for the rest of their lives. Likewise, reflux esophagitis rarely progresses to Barrett’s esophagus. Therefore, these authors believe that NERD, reflux esophagitis, and Barrett’s esophagus are three completely different diseases in the natural course of GERD in terms of pathogenesis, treatment outcome, and diagnosis of potential complications. Although there is no consensus on this subtype, scholars who hold this theory believe that this classification allows for better characterization of the various subtypes and thus better diagnostic and therapeutic approaches for each subtype.