TB Testing

Tuberculosis (TB) testing is done with a skin test also known as a PPD test. PPD stands for purified protein derivative and is used to determine if you have ever come in contact with the bacterium that causes TB. The test is administered in two visits to the doctor’s office.

At the first visit, a medical history will be taken as well as determining if the patient is from a foreign country. If you were born outside of the United States, you may have been given a vaccine which can lead to false positives. Absent the vaccine, you will be given the shot. The needle is placed under the top layer of skin and the PPD is injected forming a small bump or welt. This bump usually goes away in a few hours.

After 48 but no more than 72 hours, you must return to the doctor’s office. The doctor or medical assistant will check to see if you had a strong reaction to the test. The test is “read” by measuring the degree of reaction to the PPD.

A negative reaction means you have never been exposed to the bacterium that causes the disease. This means that the area where the test was administered is not swollen or is very small.

A positive reaction means that you have been exposed to the disease. In reading the test results, your medical or work history will play a role.

  • A 5 mm welt will be considered positive if you have HIV, have had an organ transplant, have been in close contact with someone who has active TB or a suppressed immune system.
  • A 10 mm welt will be positive for people with diabetes, healthcare workers, drug users or people who work in prisons, homeless shelters or nursing homes.
  • A 15 mm welt will be positive for people with no known risks.

A positive test does not mean that the disease is active. For that determination, more tests will be required. If you need the test, please schedule an appointment at one of our local clinics.

Our Neighborhood Walk-In Clinic is:

  • Walk-in friendly
  • Open 7 days a week 8am-8pm
  • In-network for most Washington insurers
  • Open extended hours
  • Equipped with X-Ray and Lab on-site
  • Staffed by Doctors, Physician Assistants, and Nurse Practitioners