Medical emergency. Anaphylaxis (or an anaphylactic reaction) is a medical emergency due to a severe allergic reaction. Symptoms include shortness of breath, stridorous breathing, cyanosis, cough, etc. This is a medical emergency that requires immediate treatment and/or a 9-1-1 call.
History, exam, tests. Just like any other medical condition, anaphylaxis is diagnosed by the patient see a physician, taking an appropriate history, performing and examination and, if needed, ordering allergy testing.
Clinically. Anaphylaxis is usually a clinical diagnosis, which means a history, signs, and symptoms that are consistent with anaphylaxis gives you the diagnosis. A serum tryptase level, if ordered in time, can also be helpful.