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Friday, March 6, 2015
Size of Induration (Reaction) That Makes a TB Test Positive
I want to know the size of induration that makes a TB test positive.
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:
- You have spent time with a person known to have active TB disease or suspected to have active TB disease.
- You have HIV infection or another condition that puts you at high risk for active TB disease.
- You think you might have active TB disease.
- You are from a country where active TB disease is very common (most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia).
- You live somewhere in the United States that active TB disease is more common such as a homeless shelter, migrant farm camp, prison or jail, and some nursing homes).
- You inject illegal drugs.
Lisa A Haglund, MD
Associate Professor of Clinical Medicine
College of Medicine
University of Cincinnati