Philadelphia City Branding Image

Division of Disease Control

Text Size:

Tuberculosis Testing

Who Should Get Tested

People should get tested for TB by their doctor or local health department if they:

  • have spent time with a person known or suspected to have active TB disease
  • have HIV or another condition that weakens their immune system
  • have symptoms of active TB disease
  • are from a country where active TB disease is very common;
  • live where active TB disease is more common such as a homeless shelter, migrant farm camp, prison or jail, or some nursing homes)
  • inject illegal drugs

Testing for TB Infection

There are two kinds of tests that can be used to help detect TB infection – the Mantoux TB skin test and special TB blood tests.

A positive TB skin test or TB blood test only tells that a person has been infected with TB bacteria. It does not tell whether the person has Latent TB Infection (LTBI) or active TB disease. More tests, such as a chest x-ray and a sample of sputum, are needed to see whether the person has active TB disease.

Mantoux TB Skin Test
The Mantoux TB skin test is performed by injecting a small amount of fluid (called tuberculin) into the arm. After getting the injection, the person must return within 2 to 3 days to have a trained healthcare worker look for a reaction on the arm.

Special TB Blood Tests
The special blood tests (interferon-gamma release assays, or IGRAs) measure how the immune system reacts to the bacteria that cause TB. Since they are relatively new, few health departments offer these blood tests. The PDPH does not currently offer this test, but can recommend providers that do. The T-SPOT® TB test is an example of a special TB blood test. Learn more about IGRA tests.

Testing for TB in BCG-Vaccinated Persons
BCG, or bacille Calmette-Guérin, is a vaccine for TB disease. Many people born outside of the United States have been BCG-vaccinated. BCG vaccination can cause a positive reaction to the TB skin test, even if they don't have TB. This might complicate decisions about prescribing treatment. The special TB blood tests are not affected by prior BCG vaccination and are less likely to give a false-positive result. Learn more about the BCG vaccine.

Where to Get Tested

Most health care providers can refer people for TB testing. If you do not have a primary care physician or insurance, we provide low-cost exams, testing and diagnosis at our health centers.

What to Do About a Positive Test

If a patient tests positive for TB, he or she may be referred by the doctor or health care facility to the Tuberculosis Control Program to receive free treatment and services. In all cases, the TB Control Program maintains the patient's confidentiality.