how long between ppd testing
PPD skin test. The PPD skin test is a method used to diagnose silent (latent) tuberculosis (TB) infection. PPD stands for purified protein derivative. You will need 2 visits to your doctor's office for this test. At the first visit, the health care provider will clean an area of your skin, usually the inside of your forearm. You will get a small shot (injection) that contains PPD. The needle is gently placed under the top layer of skin, causing a bump (welt) to form. This bump usually goes away in a few hours as the material is absorbed. After 48 to 72 hours, you must return to your provider's office.