When done correctly, PCN skin testing is highly predictive of serious, anaphylactic reactions.
The negative predictive value of penicillin skin testing for immediate reactions approaches 100%
Rarely (1-3%), skin test negative patients may get mild hives and itching following penicillin administration but these RESOLVE with oral antihistamines.
Skin test positive patients are at high-risk (50-75%) for serious IgE-mediated reactions with PCN exposure, and should avoid PCN agents or undergo a PCN desensitization procedure if no alternative agent exists.
Skin tests cannot predict non-IgE mediated dermatologic reactions (delayed morbilliform rash or SJS/TEN), GI disturbances, or drug fevers.
Allergy consultation is advised