What is TB Skin Test? When do we need It?

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis bacteria. These bacteria are spread through the air from infected persons and can enter and grow in the lungs, causing initial symptoms of chest pain and productive cough. If left untreated, TB can spread to other organs of the body and cause more severe or even fatal complications.

People who come into contact with TB bacteria don’t usually develop active TB immediately, as their immune system is able to mount an immune response that contains the bacteria and keeps it from infecting the body. When this is the case, the patient is said to have a “latent” TB infection. The tuberculin skin test is one way to demonstrate the presence of a latent TB infection by measuring the body’s immune sensitization to the TB bacteria. The test is performed by injecting a small amount of purified protein derivative (PPD) solution just under the patient’s forearm. The PPD solution contains inactivated TB bacteria, and people will develop redness or swelling at this site if they have been exposed to TB previously. The skin test is examined for swelling 2-3 days after the injection to determine if there was a reaction.


There are instances where the TB skin test can be falsely negative due to weakening of a person’s immune response to TB over time, as in the case of people who were exposed to TB many years ago. If the first skin test is negative, a second skin test may be performed one to weeks later, assuming that by then the first test stimulated the immune system enough to allow it to react to a repeat test if the person was previously exposed to TB. If the second test comes back negative, it is considered a true negative. If the second test comes back positive, further testing must be done to determine the status of the person’s TB infection.

3- Who Needs a TB Skin Test

Some people should get tested because they are likely to suffer from TB infection. People who must consider TB skin test are:

  • Anyone who has spent time with the person suffered from TB infection.
  • People who are suffering from any immune system problem must think about to get tested for TB infection.
  • People who suffer from HIV infection also need to get through TB skin Test.
  • People from the place where TB infection is common must get through a TB skin test to screen active or latent infection like Latin America, Russia, the Caribbean, Asia, Africa, and Eastern Europe, etc.
  • People who are suffering from TB infection symptoms like fever, cough, weight loss and night sweats.
  • People who have lived in any rehab center or correctional institutes must think about to get TB skin test.
  • People who are working somewhere where Tb infection is more common as compared to other places like jail or prisons, nursing homes, homeless shelters, rehab centers, or correctional institutes.
  • People who used to smoke or illegal drugs.

The USPSTF (the United States Preventive Services Task Force) and CDC (The Centers for Disease Control and Prevention) highly recommend TB skin testing for the people who are at more risk for TB infection.

Online Appointment!

Online Appointment

Stay Healthy!! Stay Strong!!

To make an appointment online at Southern Nevada Occupational Health Center (SNOHC), click here and file the form or call us at (702) 380-3989

Click Here →