PPD reading question

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Senior Member
7+ Year Member
15+ Year Member
Feb 28, 2002
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This is to any nurse who deals with PPD readings and really knows their stuff. Do you know if having a PPD done within a month of your last one can lead to a false positive, or simply a larger reaction? I had a patient who I diagnosed with TB, active, and I had been around her for a few times trying to fix her cough before I diagnosed the TB. Coincidentally, I had done my annual PPD the week before, and it was negative. Now, one and one half months later, I am 24 hours into my PPD and my arm has some slightly significantg erythema. I know I need to wait until the 48-72 hour mark, but I am concerned because my last test did not even leave any redness. I seem to recall that there is some sort of problem with giving them too close together. Does anyone really know, and can you give a link to reference? I have also heard that there can be a little redness at the 24 hour mark from the injection, but I didn't have any last time. I don't think I feel any induration right now, but I am getting nervous. Any insight will be appreciated. Thanks.

Matt, PA-C


10+ Year Member
15+ Year Member
May 3, 2001
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I just had my PPD done last week. Employee health wasn't sure if it was positive or negative. There were several opnions among the EH nurses. They wen't ahead and did a CXR and it was - for active TB. They told me to wait at least two weeks and come back down to have another ppd done. I was exposed 6 months ago to a pt w\active TB. BTW- what does the "-C" mean in "PA-C"?