How Does a TB Skin Test Work?

Many employers require a tuberculosis skin test as part of the pre-employment process. Also called tuberculin test or PPD test, a TB skin test determines if a person has been infected by tuberculosis bacteria. Since tuberculosis can live in the body without any symptoms (called latent TB infection), this test is crucially important for employees who may be working directly with people, as TB is easily spread from person to person through the air.

The TB Skin Test Process

In general, here’s how the TB skin test is administered:

  • A practitioner will inject 0.1 mL of liquid that contains five tuberculin units (TU) of purified protein derivative (PPD) into the top layer of the skin, typically in the forearm.
  • A wheal, which is a pale elevation of the skin, should show up in the injection spot and then be quickly absorbed into the skin. If this happens, it means the test was properly administered. If it doesn’t, a new injection is needed.
  • Over the next day or so, a small, raised, hard area will appear at the site of the injection. This is called an induration and it is how the TB skin test is read.
  • Within 48 to 72 hours, the patient will need to return to the clinic so the practitioner can measure the diameter of the induration. In a healthy patient with no apparent risk factors, an induration of 15 millimeters or larger will be considered a positive result and require treatment.

PPD Skin Tests at CommunityMed Family Urgent Care

At CommunityMed Family Urgent Care, we offer a number of occupational health services for the North Texas community, including PPD skin tests for tuberculosis. If you’re in need of one of these tests, stop by one of our walk-in clinics to receive prompt service. We are open seven days a week until 8 p.m. for your convenience.