It indicates that you have been exposed to tuberculosis antigen recently/ or sometime in the past. Please see a chest physician/ TB specialist as active tuberculosis needs to be ruled out with complete history and examination.

For a positive mantoux test the swelling or the induration diameter and not the redness should be more than 5 to 15 mm , best read by a tb specialist after 48 to 72 hours after the test. However , there is no correlation between the size of induration and likelihood of current active TB disease but the reaction size is correlated with the future risk of developing TB disease. The test has a poor positive predictive value for current active disease. Best interpretation should be done keeping in mind the symptoms and after proper evaluation by a pulmonologist and taking help of other investigations if available like X-ray chest , sputum examination , sputum microscopy for tb etc for the confirmed diagnosis of an active tb disease.

Hi. I understand your concern. You will need to undergo a detailed examination and investigation. Consult a pulmonologist for the same at the earliest

First of all, what was the reason why  the test was offered to you. Now as you mentioned swelling and redness, is 20mm - this may not be the correct method of measurement as we need to know only the measurement of swelling. Please visit your doctor who had adviced the test.