Hello dear, Thank you for your contact to health care magic. I read and understand your concern. I am Dr Arun Tank answering your concern. Tuberculin test or mantoux test is the test to know allergic reaction to protein part present in the body because of the infection. If you are infected with tuberculosis, you have infected protein in the body. And so you are allergic to the protein part. The reaction will start after the 48 hours. So you have to wait 24 hour more to start up reaction. If you have spent time in the tuberculosis prone country you will be exposed to the infection and so you are prone to the positive reaction. Positive reaction dose not mean you are having a TB right now. Instead it means you are exposed to the infection once. Induration in the reaction is counted while erythema and wheal is ignored. If the horizontal diameter of the reaction is more than 10 mm than it is positive reaction. I will be happy to answer your further concern on bit.ly/DrArun. Thank you, Dr Arun Tank Infectious diseases specialist, HCM.