Question: Are there lab tests that can be done to determine if a reaction was due to anaphylaxis?
Answer: The diagnosis of anaphylaxis is not typically made by a laboratory test. It's made by the clinical history. An allergic patient is exposed to an allergen and, within minutes to hours, develops progressively worsening allergic symptoms in several different organ systems. If a patient is seen during the middle of an episode of anaphylaxis, blood can be drawn to check for allergic mediators.
Typically we check for tryptase, which is an enzyme that's released by the mast cell, which is a central cell in the allergic response. When a patient has a severe allergic reaction, the mast cell releases tryptase into the tissues that then gets into the blood stream and can be measured. The level of tryptase increases after an allergic reaction, although not all patients who have anaphylaxis have an elevated tryptase level.
More importantly, once the patient has recovered from the anaphylactic event, it's important that they see an allergist who can help them determine if they're sensitized to one of the allergens to which they were exposed prior to the allergic reaction or the anaphylactic event. This will be performed by skin testing and measuring levels of allergy antibody in the blood to different allergens to which the patient was exposed before the event. Thus, the demonstration of sensitization to an allergen followed by a reaction upon exposure to that allergen is what helps make the diagnosis of anaphylaxis.