The tuberculin test, also known as the PPD test, is a method of diagnosing tuberculosis infection and can be used to diagnose tuberculosis disease or to provide a basis for the success of BCG vaccination. The main procedure is to inject 0.1 ml (5 units) of tuberculin into a smooth area on the flexor or lateral side of the forearm without any lesions, and then mark the area with a marker. Normally, a 6-10mm white bump, or mound, will appear on the skin, so be careful not to press or rub it. After the injection, the doctor will measure and record the size of the local mound and observe the result 48-96 hours after the injection (the best time is about 72 hours after the injection), paying attention to the size of the local mound, the presence of hard nodules, and reactions such as blisters and rashes. The normal result is a papule of less than 5mm and no nodules. If there are nodules with a papule larger than 5mm, it is a pathological reaction. A nodule of 5-9mm is positive, 10-19mm is moderately positive, and greater than or equal to 20mm is strongly positive, and lesions with blisters and rashes are very strongly positive. In addition, there is no need to be overly nervous about a positive tuberculin test, as it does not necessarily mean that it is a tuberculosis infection, and a positive reaction may occur if BCG vaccination has been administered. Tuberculosis infection needs to be diagnosed by further imaging, laboratory tests and clinical symptoms under the guidance of a doctor, such as CT results, routine blood test results, sputum test results, or the presence of symptoms such as cough, sputum, low afternoon fever, night sweats, and fatigue. In addition, if tuberculosis is diagnosed, prompt treatment at an infectious disease clinic is required. At the same time, some people have contraindications to tuberculin testing, such as those who are in a disease attack, have a history of allergy or hysteria. Such people should be examined with the consent of the doctor. If there is any obvious discomfort during the injection, the doctor should be informed promptly and the injection should be stopped.