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Infectious Diseases

TB testing



How long does it take for a Mantoux to clear out of a 40lbs child`s system? My son was given this test twice, the second one a week after the first one. A third test is being recommended after 30 days have passed from the last test. Are 30 days enough? I just want to avoid a false positive result due to tuberculin residue left in his system. Thank you!


As long as a standard Mantoux TB skin test with 0.1 ml of 5TU PPD is being given, there will not be a false positive with subsequent Mantoux testing. This was a problem with the much more concentrated 250TU PPD preparations that were used in the past. Currently, there is no indication for use of the 250TU PPD for Mantoux testing.

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Response by:

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