8 doctors weighed in:

Why do nursing homes use double PPD testing?

8 doctors weighed in
Dr. Simon Tsiouris
Internal Medicine - Infectious Disease
6 doctors agree

In brief: Older immune system

An elderly person's immune system can sometimes not react very strongly or at all to the first PPD test (even if the patient has been infected with tb) and lead to a false negative result.
But the false negative PPD can 'prime' the immune system so that a second test done two weeks later will give a true positive result.

In brief: Older immune system

An elderly person's immune system can sometimes not react very strongly or at all to the first PPD test (even if the patient has been infected with tb) and lead to a false negative result.
But the false negative PPD can 'prime' the immune system so that a second test done two weeks later will give a true positive result.
Dr. Simon Tsiouris
Dr. Simon Tsiouris
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1 comment
Dr. Larry Lutwick
The significance of a positive 2-step PPD is not clearly the same as a 1-step. We do not know if the risk of reactivation is the same and some have suggested that it reflects a much lower risk.
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