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TB (tuberculosis) Tests Available
The Braintree and Natick offices offer two TB tests options:
- Tuberculin Skin Test (TST)
- QuantiFERON-TB Gold (IGRA blood test)
What is a TB Skin Test?
Also known as a TST or PPD test, the TB skin test helps determine if a person has a past exposure to the bacterium that causes tuberculosis infection. A small amount of purified protein derivative (PPD) is placed under the skin to create a bump called a “wheal.” To complete the test, you must return 48-72 hours after placement and have the skin inspected and “read.” For some schools and employers, a two-step skin test is required to determine your baseline TB status. In a two-step test, the TST is repeated 7 days after the 1st test is read.
What is a TB Blood Test?
The QuantiFERON-TB Gold is a type of IGRA (Interferon Gamma Release Assay) test to check for past tuberculosis infection. The blood test is completed in a single visit and the sample is sent to a laboratory for testing. Results post within a few days. If you have been previously vaccinated with BCG (bacille Calmette-Guérin), the IGRA test is preferred over the skin test as it does not produce a false-positive result.
Is a TB Vaccine Available in the United States?
In many countries with higher risk for tuberculosis infection, the BCG ( bacille Calmette-Guerin) vaccine is given to infants and small children. In the US, the BCG vaccine is not readily available and only given by public health officials in specific situations. The BCG vaccine is not recommended for international travelers.
Who Needs TB Testing?
Many health care professionals require tuberculosis testing at time of hire and certain higher risk groups need yearly testing like respiratory therapists and emergency department employees. When exposure to a person with tuberculosis occurs, testing is recommended immediately afterward and again 8-10 weeks following the exposure.
Not only is baseline TB testing a requirement for credentialed medical professionals, but many allied health programs require students to submit a negative test before beginning courses. This includes students in nursing, medicine, physical therapy, patient care technicians, emergency medicine technicians (EMTs), and dentistry among others.
Additionally, people with plans to travel internationally may need a TB test before leaving, especially if they have plan to stay for more than a month, volunteer in a medical clinic or refugee camp, or have a weakened immune system.
Immigration Exam (I-693) and TB Testing
Guidelines from U.S. Citizenship and Immigration Services (USCIS) requires all applicants 2 years and older to receive a tuberculosis IGRA blood test. The results of the test are documented in Part 8 of the I-693 Form. The only accepted IGRA tests are the QuantiFERON® (TB Gold) or Oxford T-SPOT®.
What if My TB Test is Positive?
If a TB test (skin or blood) returns positive, additional testing is needed, often involving a chest x-ray and sputum sample to determine if the infection is current (active) or past (inactive). Many people worldwide have been exposed to the tuberculosis bacteria and develop a latent (dormant) infection. While a person with a latent infection cannot spread the disease to others, sometimes the infection can reactivate later in life and medication is given to prevent this from happening. Read more about tuberculosis from the CDC.
