What happens when a ppd test is too deep? can it cause the area to turn red?

Less Reliable: If the PPD test is too deep it usually is not as effective. It can turn the area red, just like the regular test, and if you have tb, might harden like the typical test, but is less likely to do so. A TB test is considered positive when an area bigger than a dime is firm to touch. It should be repeated if it was administered improperly.