What is a Two-Step PPD test? Is this a new type of PPD test? How long should you wait in between tests?

Question

What is a Two-Step PPD test? Is this a new type of PPD test? How long should you wait in between tests?

Answer 1

This is an altenative testing method screening for people who are remotely exposed to tuberculosis, say many years before the test.  The initial test is injected and read normally, then repeated in 1-3 weeks if negative.

If the second test is positive, it is very unlikely the person was exposed to and formed antibodies in that short period of time.  The current theory is that the immune system, which recognizes the proten but is not prepared to react to it, is "boosted" by the first PPD and then primed to react to the second.

Generally, it is used in healthcare and nursing home workers to demonstrate that the "new" positive test is not due to exposure to patients in their care, as that would have significant public health implications.

If you have had a PPD within the last 5-10 yrs, it is unlikely that you would have a "booster" reaction as your immune system has already been primed.

Answer 2

Step 1. You get the test.

Step 2. You come back 48-72 hours later to get it read.  They tell if there is any induration (hardness) or redness.

This is why they are generally not done on Thursdays.