Inclusion Criteria:

• Male and females, ≥ 18 years of age.
• Adults identified by a specialist as having a potential immunologically mediated reaction to a drug or externally administered substance during an acute event (i.e., perioperative anaphylaxis, drug challenge, etc.) or diagnosed by in-vitro and/or in-vivo testing after a reaction has occurred.
• Subjects must provide informed consent. For each subject included, a control will be recruited: a patient exposed to the causal agent without evidence of an immediate drug allergy or having a negative drug allergy test/ drug challenge.

Exclusion Criteria:

• Male and female, < 18 years of age.
• Adults identified by a specialist to as having an immediate drug reaction that is likely related to an immunologically mediated reaction associated with a drug or externally administered substance.
• Adults unable to provide informed consent and a decision maker/surrogate is not available.