when does tb test need to be read
Skin tests should be read 48-72 hours after the injection. The basis of the reading of the skin test is the presence or absence and the amount of induration (localized swelling). A negative test does not always mean that a person is free of tuberculosis. A person who received a BCG vaccine (administered in some countries but not the U.S.) against tuberculosis may also have a positive skin reaction to the TB test.