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Tuberculosis

Size of Induration (Reaction) That Makes a TB Test Positive

11/06/2008

Question:

I want to know the size of induration that makes a TB test positive.

Answer:

If a person is immunocompromised, such as HIV-infected or an organ or marrow transplant recipient, or if the person has an abnormal chest x-ray suggestive of TB, or if the person was recently exposed, >5 mm of induration is a positive PPD skin test.

If a person is a health care worker, or has other medical conditions that would predispose to TB exposure or disease, >10 mm induration is a positive PPD skin test.

For all other people (without risk factors for TB exposure or disease), >15 mm induration is a positive PPD skin test.

In general, the CDC recommends that you should get tested for TB if:

For more information:

Go to the Tuberculosis health topic, where you can:

Response by:

Lisa A Haglund, MD Lisa A Haglund, MD
Associate Professor of Clinical Medicine
College of Medicine
University of Cincinnati