How to Read a Ppd Intradermal TB Test

The intradermal PPD (purified protein derivative) or Mantoux test refers to the common test for tuberculosis (TB). TB is a disease affecting the lungs, and is highly contagious. The intradermal PPD test is usually required of health care personnel, those who work in education, and is recommended for anyone with suspected exposure to the tuberculosis virus. The test consists of injecting the extract just under the skin of the forearm, and then rating the reaction.

Things You'll Need

  • Ruler or measuring Tape

Instructions

    • 1

      Read tuberculosis test results between 48 and 72 hours after the PPD intradermal test is administered.

    • 2

      Use a ruler or measuring tape, and measure the diameter of the largest portion of the raised bump at the TB test site (known as induration). Record the measurement in millimeters (mm.). Do not measure red areas if they aren't raised.

    • 3

      A measurement of greater than or equal to 15 mm. at the PPD intradermal test site is considered positive in a healthy person with no known exposure to TB.

    • 4

      A measurement of 10 mm. or greater at the PPD intradermal test site is considered positive in a person with underlying diabetes, kidney disease or a health care worker or other person with likely personal contact to a TB patient.

    • 5

      A measurement of 5 mm. or greater at the PPD intradermal test site is considered positive for tuberculosis in a person with underlying autoimmune disease, such as HIV or Crohn's.

    • 6

      Check for major blistering at the test site. Blisters are always considered a positive TB test result.

Tips & Warnings

  • Recent vaccinations with live viruses or use of immunosuppressive drugs can result in false negative test readings.
  • A previous BCG vaccination can result false positive test readings.
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