Based on serum gastrin and gastric acid secretion, highly differentiated gastric neuroendocrine tumors are clinically classified into 3 types: type 1 (associated with type A atrophic gastritis), type 2 (associated with gastrinoma) and type 3 (disseminated, independent of serum gastrin levels). Hypofractionated neuroendocrine carcinoma as well as mixed adenoneuroendocrine carcinoma belong to type 4. Both type 1 and type 2 have hypergastrinemia (elevated serum gastrin levels); the main difference between them is that type 1 patients have a lack of gastric acid secretion and have a background of type A atrophic gastritis; patients’ clinical manifestations may be belching, epigastric fullness, or dizziness and weakness (symptoms of anemia) without heartburn and acid reflux. type 2 patients have excessive gastric acid secretion caused by gastrinoma (Zhuo-Ai syndrome); clinical manifestations are intractable Type 3 patients do not have hypergastrinemia and have normal serum gastrin and normal acid secretion. The lesion in the stomach is solitary and the tumor is usually large, 2 cm or more. In patients with a growth in the stomach and a biopsy pathology that reveals a gastric neuroendocrine tumor, the first step is to do a serum gastrin test. Elevated serum gastrin belongs to type 1 or type 2, and normal serum gastrin belongs to type 3. The next step can be gastric 24-hour pH monitoring. Type 1 patients have gastric acid deficiency, type 2 have excessive gastric acid, and type 3 have normal gastric acid secretion. The clinical staging of gastric neuroendocrine tumors determines the treatment strategy, and the prognosis and survival of patients with different staging varies. Therefore, for patients with gastric neuroendocrine tumors, in addition to testing serum CgA (a universal marker for neuroendocrine tumors), serum gastrin testing is also essential.