Could a TB skin test be false positive if the needle was to deep? My arm bled after the test and now that its healing I have a large purple bruise
Wouldn't accept it. The test is standardized to represent the reaction to material places between layers of your dermis (skin) and would become invalid if it went too deep and bled. It deserves repeating.I would worry that it could be falsely negative if the test material dissipated into deep tissue.That could lead to a delay in proper treatment. A false positive would be unlikely& need eval.
Yes. it is the induration you should look for.An accurate test is not applied so deep.