The ppd (tuberculin test) has a 3cm red halo but no hard nodules suggesting a negative tuberculin test, and the presence of pulmonary tuberculosis should be evaluated in conjunction with the patient’s symptoms, signs, and imaging studies. The PPD skin test, also known as the tuberculin test, is a skin test using tuberculin to determine whether the body can cause a hypersensitivity reaction to Mycobacterium tuberculosis. Tuberculin is usually injected intradermally into the palm side of the patient’s forearm, and the results of the reaction are observed after 72 hours, with the size of the diameter of the localized hard nodule being used as a criterion for determining the result. A scleroderm is a raised bump above the skin, which is a metaplastic reaction, and a red halo around it is a nonspecific metaplastic reaction. If there are no nodules, the redness alone is a negative sign. Clinical judgment of the results of tuberculin test is mainly based on the diameter of the local nodule, less than 5 mm is negative, 5-9 mm is positive, 10-19 mm is moderate, positive more than 20 mm or less than 20 mm, but there are blisters or necrosis is a strong positive performance. In the clinical suspicion of pulmonary tuberculosis patients, tuberculin test can not be used as a basis for diagnosis, need to be combined with the patient’s clinical symptoms, imaging tests, sputum examination and other comprehensive diagnosis.