General Information About the Test
Test Process and Preparation
A very small dose of PPD fluid is injected just under the skin (intradermally) on the arm using a very fine needle, similar to an insulin syringe. The procedure takes seconds. A small, white blister forms at the injection site.
Exactly 48 to 72 hours after the test is administered, the patient must return to the hospital. The physician evaluates the result by measuring the diameter in millimeters (mm) of the "induration and hardness" felt by finger at the injection site, not the "redness", using a special ruler.
A positive PPD test alone does not indicate that you are an active tuberculosis patient. The test can also be positive (raised) in individuals who have received the tuberculosis vaccine (BCG). When a positive result is detected, a chest X-ray is taken to rule out active disease, and preventive treatment is given if necessary.
The information on this page is for informational purposes only. The results of medical tests must be evaluated by specialist physicians.
