C14 is generally referred to clinically as the C14 breath test, a method of detecting H. pylori using breath. The normal reference range is 0-100 (dpm/mmol CO2), and a value above 100 (dpm/mmol CO2) is considered positive and indicates the presence of H. pylori infection, but may not affect the severity of the patient’s condition. Usually a high value of C14 H. pylori is not exactly proportional to the severity. The principle of detecting H. pylori using the breath test is that when a capsule containing C14 is swallowed, the urease produced by H. pylori in the stomach breaks down the urea to produce carbon dioxide. The presence or absence of H. pylori infection is determined by measuring the number of carbon dioxide labeled by C14 in the breath. Therefore, if the H. pylori infection is high or if the urease activity produced is high, it will affect the value of the test. In addition, the results can be biased if the subject is not fasting, if there is food in the stomach or for other reasons such as improper handling during expiration or too long or too short expiration time. In general, the detection of H. pylori infection should be followed by gastroscopy and history taking to determine the extent of damage to the gastric mucosa caused by the patient’s H. pylori infection and the need for sterilization treatment, and the severity of the infection should not be judged solely on the basis of the values.