How to Read a PPD Test

Tuberculosis is a bacterial disease that affects the lungs. It is difficult to treat because it is resistant to most antibiotics and often is treated for months. Tuberculosis can be fatal if left untreated. The bacteria can spread through the bloodstream and cause infection in other areas of the body. Health care workers are often required to be tested for exposure to TB. The most common test is the injection of PPD -- purified protein derivative -- which is an antigen of TB underneath the skin. The test is read between 48 and 72 hours after the injection.

Things You'll Need

  • Pen or semi-permanent marker
  • Adhesive bandage


    • 1

      Mark the injection site by drawing a small circle on the patient's forearm. As an alternative, place a small adhesive bandage over the injection site and instruct the patient to keep it covered until he has the test read. If the test is negative, it might be difficult to know where the injection was placed. Instruct the person to return within 48 to 72 hours.

    • 2

      Examine the patient's arm at the injection site. If the skin is flat and flesh colored, the test is considered negative. If there is a red, raised bump at the injection site, she might have been exposed to tuberculosis.

    • 3

      Perform further diagnostic testing for patient's with a positive PPD test. This includes blood work, chest X-ray and sputum analysis. These tests will confirm a diagnosis of TB.

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