What Is PPD When Testing for Tuberculosis?

Tuberculosis most often infects the lungs.

Tuberculosis is a potentially deadly bacterial infection that is spread from one person to another by coughing or sneezing. This infection can be identified by using a purified protein derivative (PPD) test.

PPD Test

The PPD or Mantoux test is a simple procedure. The healthcare worker injects a small amount of purified protein derivative--a liquid-encased solution of inert tuberculin bacterium--just under the skin of the forearm. A person who has already been exposed to the tuberculosis bacteria will have antibodies that remain in the system. The PPD test will cause those antibodies to react.

Reaction

A patient who has been injected with PPD must return 48 to 72 hours after the test is completed so that the doctor can check for a reaction. The doctor will look for a raised lump under the injection site. If a bump is present, he will measure it to see how large it is. A large lump usually means that infection is present.

Misconceptions

Many people are concerned that there is live or dangerous bacterium in the PPD solution. According to Rutgers University, there is no live bacteria in the solution, so it is incapable of causing a tuberculosis infection.

References

• Net Doctor: Tuberculin Purified Protein Derivative (PPD)
• Rutgers University: Tuberculosis (TB) Test Information