A purple bruise after a skin test may be caused by a small amount of subcutaneous bleeding due to inadequate local pressure and time, when the subcutaneous bleeding turns purple or purplish due to loss of oxygen. If the tuberculin skin test is performed and the injection site is purplish red and hard nodules appear, it suggests the previous presence of tuberculosis or is in the stage of tuberculosis infection at this time.1. Subcutaneous bleeding: usually caused by insufficient pressure and time, usually no treatment is needed and the torso can be gradually absorbed. If the bleeding area is large, it can also be relieved by applying heat 2 hours after the end of the local injection. But need to carefully observe whether the bleeding area continues to expand, if it continues to expand also need to go to the hospital for coagulation-related examination to exclude coagulation dysfunction; 2, positive nodule test: can be manifested as a purplish red injection site or the appearance of redness, and hard nodules, or even blistering or necrosis, usually indicates a positive or strong positive skin test results, indicating that this patient has a previous history of tuberculosis or the current stage is in The patient should be treated with anti-tuberculosis therapy, such as isoniazid, rifampin, and streptomycin and kanamycin, depending on the circumstances. Chemotherapy is required in some patients, but early, appropriate, combined, regular, and full treatment should be followed to facilitate treatment. In addition, subjects should be aware that if metaplasia occurs within 72 hours after the skin test, possibly due to different body types, manifesting as itching and fever, they should not scratch with their hands at this time to avoid infection, nor should they apply any topical drugs on their own to avoid affecting the skin test results.