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Tuberculosis

Abnormal reaction to PPD test

10/31/2007

Question:

I got a PPD test for tuberculosis on Wednesday. When I went back on Friday to have it read, it was slightly red but had no induration or anything, so the nurse said it was negative. When I got up this morning- Sunday (4 days later) the area that was red was still red and now had tiny rash like bumps, about the size of a pen point and barely raised. It worries me a little, but it doesn`t look like the positive tests that I keep seeing online and in my medical books. I think it may be reaction to the PPD test itself or the band-aid- I`ve had horrible reactions to bandages in the past, but didn`t think about it until it was on for like 8 hours. What do you think?

Answer:

Your reaction sounds more like a contact dermatitis from the bandage than due to the PPD test, but I would have your physician re-evaluate to make sure. There are four main reactions to PPD:

1) Early reaction: This is greatest within 2-6 hours after a PPD is placed. The site is swollen, red, and occasionally bruised. This is also known as an Arthus reaction

2) Retest reaction: This begins about 3 hours after PPD placement, and resolved by 72 hours. It is caused when a new PPD is placed in the same site as a previous one.

3) Basophil Hypersensitivity: This is less swollen and more red than a typical PPD, occurs within 4-6 hours of placement and is greatest by 24 hours. This reaction is thought to only occur in patients with latent or active tuberculosis.

4) The classic PPD reaction: This begins 4-6 hours after placement, peaks at 48 - 72 hours (best read at 48 hours) and is based on the degree of swelling, not redness.

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Response by:

J Daryl   Thornton, MD, MPH J Daryl Thornton, MD, MPH
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University