PPD or Purified protein derivative or Tuberculin test or Mantoux test tb is used to diagnose Mycobacterium tuberculosis. It is used to check the hypersensitivity of individuals to TB.
Purified protein derivative test (PPD) Procedure
There are various doses of tuberculin like 1 TU, 5 TU, 10 TU, 250 TU. But mostly 5 TU is used.
- Intradermally injecte 0.1 ml ppd after cleaning the site with antiseptic.
- Read the induratiom after two to three days.
- If induration is more than 10 mm after three days, than PPD skin test consider as positive.
PPD skin test (mantoux test tb) reading
Positive PPD test: If ppd test induration is more than 10 mm after ppd intradermally injection then the test result is positive. The patient has had or has live tuberculosis in his body.
Negative PPD test: If there is no ppd induration after (72 HOURS) PPD intradermally injection then the test result is negative. It means the patient has not had primary tuberculosis.
False-positive TB test (PPD)
In the case of BCG vaccination, false-positive results can occur.
False-negative TB test (PPD)
There are the following cases that result in false PPD negative results..
- Recent Tuberculosis Infection.
- Very young age (less then six month)
- Live verus vaccine
- End renal Disease
- Poor nutration
- Hodgkin’s disease