<unk>  is diagnosed on the basis of a person's signs and symptoms. When any one of the following three occurs within minutes or hours of exposure to an allergen there is a high likelihood of<unk> : # Involvement of the skin or mucosal tissue plus either respiratory difficulty or a low blood pressure causing symptoms # Two or more of the following symptoms after a likely contact with an allergen: #: a. Involvement of the skin or mucosa #: b. Respiratory difficulties #: c. Low blood pressure #: d. Gastrointestinal symptoms # Low blood pressure after exposure to a known allergen Skin involvement may include: hives, itchiness or a swollen tongue among others. Respiratory difficulties may include: shortness of breath, stridor, or low oxygen levels among others. Low blood pressure is defined as a greater than 30% decrease from a person's usual blood pressure. In adults a systolic blood pressure of less than 90 mmHg is often used. During an attack, blood tests for tryptase or histamine (released from mast cells) might be useful in diagnosing<unk>  due to insect stings or medications. However these tests are of limited use if the cause is food or if the person has a normal blood pressure, and they are not specific for the diagnosis. Classification There are three main classifications of<unk> . * Anaphylactic shock is associated with systemic vasodilation that causes low blood pressure which is by definition 30% lower than the person's baseline or below standard values. * Biphasic<unk>  is the recurrence of symptoms within 1–72 hours after resolution of an initial anaphylactic episode. Estimates of incidence vary, between less than 1% and up to 20% of cases. The recurrence typically occurs within 8 hours. It is managed in the same manner as<unk> . * Anaphylactoid reaction, non-immune<unk> , or pseudoanaphylaxis, is a type of<unk>  that does not involve an allergic reaction but is due to direct mast cell degranulation. Non-immune<unk>  is the current term, as of 2018, used by the World Allergy Organization with some recommending that the old terminology, "anaphylactoid", no longer be used. Allergy testing Skin allergy testing being carried out on the right arm Patch test Allergy testing may help in determining the trigger. Skin allergy testing is available for certain foods and venoms. Blood testing for specific IgE can be useful to confirm milk, egg, peanut, tree nut and fish allergies. Skin testing is available to confirm penicillin allergies, but is not available for other medications. Non-immune forms of<unk>  can only be determined by history or exposure to the allergen in question, and not by skin or blood testing. Differential diagnosis It can sometimes be difficult to distinguish<unk>  from asthma, syncope, and panic attacks. Asthma however typically does not entail itching or gastrointestinal symptoms, syncope presents with pallor rather than a rash, and a panic attack may have flushing but does not have hives. Other conditions that may present similarly include: scrombroidosis and anisakiasis. Post-mortem findings In a person who died from<unk> , autopsy may show an "empty heart" attributed to reduced venous return from vasodilation and redistribution of intravascular volume from the central to the peripheral compartment. Other signs are laryngeal edema, eosinophilia in lungs, heart and tissues, and evidence of myocardial hypoperfusion. Laboratory findings could detect increased levels of serum tryptase, increase in total and specific IgE serum levels.
Anaphylaxis
Asthma
Heat urticaria
Allergy
Cholinergic urticaria
Carcinoid syndrome
Tachyphylaxis
Angioedema