Tuberculin test is the PPD test, which mainly uses a fine needle to inject tuberculin into the forearm under the skin, and its result is judged by 72h observation. The results are judged as follows: 1. Generally, a red spot larger than 5mm at the injection site at 72h is a negative result, indicating that the person has not been infected with TB and has not received BCG vaccine. 2. A red spot of 5-10mm indicates a weakly positive result, indicating that the person may have received TB vaccine or has been infected with TB. 3. A red spot of 10-20mm is positive, also indicating that the person may have been infected with TB or received vaccine. 4. Erythema >2cm, or blisters, hard nodules, or rupture, are considered strongly positive for TB, except for current TB infection.