It is necessary to do c14 breath test after gastroscopy, and the purpose of the two tests is different. 1. Gastroscopy: Gastroscopy can enter from the mouth and reach the esophagus as well as the stomach to observe the lesions of the esophageal mucosa as well as the lesions in the stomach, and can detect different lesions such as esophagitis, esophageal polyps, esophageal cancer, gastritis, gastric cancer, gastric polyps and so on. 2. c14 examination breath test: mainly to determine whether there is Helicobacter pylori infection, the normal value of c14 is <100bpm, if it is greater than this value, it will be judged as having Helicobacter pylori infection. The purpose of the two tests is not the same, so after the gastroscopy also need to carry out c14 breath test examination. Please follow your doctor's instructions for the specific test.