The result is measured at 48-72 hours after test,

Basically diameter more than 5mm is positive. Usually needs X-ray to confirm whether you have active lung TB or not.--If X-ray is clear, that is totally fine,means you are healthy. Either you had TB before or you had BCG (卡介苗)vaccine might be the causes--most Chinese are positive, because we got BCG shot.Unless you had an extreme reaction, like diameter more than 2mm, 水泡,壞死... and you are found something in X-ray.