The 3-step gastric function test is a non-invasive, painless, safe and economical test for gastric disease. It is mainly performed by measuring pepsinogen I (PGⅠ), pepsinogen II (PGⅡ) and gastrin 17 (G-17), and then calculating the ratio of pepsinogen I and II (PGⅠ/PGⅡ) to assist in the diagnosis of gastric mucosal diseases. Significance of the test Usually, serum gastrin, pepsin I and pepsin II are less in the blood of normal people, but will appear significantly elevated when early gastric cancer occurs. Therefore, the 3 tests of gastric function are important for diagnosing diseases of the stomach. Moreover, gastrin 17 is an important indicator of gastric mucosal damage; pepsinogen can also help determine whether the gastric mucosa is atrophic, and clarify the location and severity of atrophy, and the ratio of the two can be used to screen for atrophic gastritis. The 3 tests are usually performed on an empty stomach, so patients should avoid eating and drinking on the day of the blood draw. It is also important to avoid alcohol, greasy foods such as doughnuts and fried chicken, and stimulating diets such as strong tea and coffee in the days before the blood draw.