The tuberculosis skin test, also called the tuberculin test, determines whether the patient is infected with Mycobacterium tuberculosis by looking at the size of the local rash of hard nodules. A positive Mycobacterium tuberculosis skin test indicates a Mycobacterium tuberculosis infection, but it does not distinguish between a previous or current infection. The TB skin test is usually injected intradermally in the middle of the flexor side of the patient’s left forearm, and the results of the skin test are viewed 48 to 72 hours later. It is normal for the skin to be reddened during the TB skin test, but the size of the dermal nodule diameter should be measured to determine whether the skin test is negative or positive. skin necrosis, lymphangitis, ulceration, and double circles, the reaction can be judged as strongly positive. If the tuberculosis skin test result is negative, it means that the organism is not infected with tuberculosis bacteria. However, in immunocompromised or malnourished patients with tuberculosis, the TB skin test may also be negative. If it is weakly positive or positive, it indicates a previous TB infection, not necessarily a current disease, and if it is strongly positive, it indicates possible active TB disease. A strong positive result indicates active tuberculosis, which requires active anti-tuberculosis treatment and good ventilation.