How long a TB test is good for will depend on the patient. A TB test typically proves that you were TB negative up until the point of the test. It will not prove whether or not you have been exposed thereafter. So, your risk factor is key. If you are a healthcare worker who is regularly exposed to TB you will need to be tested regularly at the request of your employer. Someone who has no risk factors and no exposure may never need to be tested. Typically children are tested at age 1, 5 and 10 and after that just on an as needed basis. For more information look at these websites.