Usually TB skin test results change over time, usually 48 to 72 hours, and this test can make it easier for doctors to diagnose and identify TB. The TB skin test is considered to be the PPD skin test, which is a test to detect Mycobacterium tuberculosis infection. Usually, PPD skin test results will change over time, mainly to exclude the interference of non-specific reactions, to ensure the accuracy of the skin test results, usually 48-72 hours after the PPD skin test will appear the final results, during which you need to closely observe the skin test changes. PPD skin test can help doctors diagnose and identify tuberculosis. If there is only one +, it is weakly positive, which may be a history of tuberculosis; if there are two +, it is moderately positive, which indicates that the patient may have tuberculosis; if there are three + and above, it is strongly positive, which suggests that the patient is very likely to be in the prevalence of tuberculosis. To summarize, for people with abnormal PPD skin test results, further relevant examinations should be done to clarify the specific causes.