Skin testing is not advisable in people with a history of allergic reaction to TST or TBST. Allergic reactions to TST (PPD or equivalent), such as a generalized rash that occurs within the first 24 hours, are seen in less than 1% of recipients (26). If this has been well documented in the past, then it is wise to avoid repeating the test with the same tuberculin material. Currently, it is unclear whether use of an alternative tuberculin material would be safe. Anaphylaxis in response to tuberculin skin testing is extremely rare (1 per million) (27); however, if there is well-documented anaphylaxis in response to TST, then TB infection skin testing should not be performed, even with TBST, until further safety information is available.
Loss of consciousness after TST administration due to a vasovagal reaction (simple fainting) is far more common than anaphylaxis.