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ANAPHYLAXIS OVERVIEW
Anaphylaxis is a potentially deadly allergic reaction that is rapid in onset. It is most often triggered by foods, medications, and insect stings. There are many other possible triggers.
Anaphylaxis is an unpredictable condition. Many people who experience it have a known allergy and some have had one or more milder allergic reactions previously. Others, who are not even aware that they have an allergy, can suddenly experience severe anaphylaxis. Even the first episode of anaphylaxis can be fatal.
The severity of anaphylactic reactions can be minimized by recognizing the symptoms early, having proper medication available for self-treatment, and seeking emergency medical care promptly. This topic reviews the symptoms and diagnosis of anaphylaxis. Treatment and prevention of anaphylaxis are discussed separately. A separate topic discusses how to use an epinephrine autoinjector. (See "Patient information: Anaphylaxis treatment and prevention" and "Patient information: Use of an epinephrine autoinjector".)
ANAPHYLAXIS SYMPTOMS
Symptoms of anaphylaxis generally begin within minutes to an hour of exposure to a trigger. Less commonly, symptoms do not develop for several hours.
The most common symptoms of anaphylaxis are hives (urticaria) and swelling of the skin (angioedema), which occur in 80 to 90 percent of reactions. Respiratory symptoms occur in about 50 percent of reactions, and are especially common in people who also have asthma or another chronic respiratory disease. Extremely low blood pressure, causing lightheadedness, dizziness, blurred vision, or loss of consciousness (passing out) occurs in about 30 percent of reactions.
Anaphylaxis can cause symptoms throughout the body:
A severe form of anaphylaxis causes sudden collapse without other obvious symptoms, such as hives or flushing. This form of anaphylaxis occurs most commonly after a person is given a medication into a vein or is stung by an insect.
Up to 20 percent of people with anaphylaxis have biphasic (two-phase) or protracted (prolonged) anaphylaxis. A person with biphasic anaphylaxis has a reaction that resolves and then recurs hours later without further exposure to the trigger. The late phase reaction usually occurs within eight hours, but may occur up to 72 hours after the initial symptoms. A person with protracted anaphylaxis has signs and symptoms that persist for hours or even days despite treatment, although this is rare.
ANAPHYLAXIS TRIGGERS
The trigger for a person's anaphylaxis may be obvious or it may be difficult to identify.
Common anaphylaxis triggers can include:
In teens and adults, peanuts, tree nuts, fish, and crustaceans (shellfish such as shrimp) are the most common triggers.
Any food, including fruits and vegetables, and some spices and food additives, can cause anaphylaxis.
Sometimes a specific trigger cannot be identified, even after a thorough evaluation. This condition is called idiopathic anaphylaxis. (See "Patient information: Anaphylaxis treatment and prevention".)
IgE mediated anaphylaxis — In most people, anaphylaxis is caused by the presence of proteins called immunoglobulin E (IgE) antibodies. IgE antibodies are normally produced in the body for the purpose of fighting certain infections. In people with allergies, however, IgE is made in response to non-infectious substances, such as foods, medications, or insect venoms. This IgE then sticks to the outside of mast cells and basophils, a type of white blood cell.
If a person with IgE antibodies to a specific allergen is exposed to that allergen again, the cells may suddenly become activated. The activated cells release large amounts of inflammation-causing chemicals (including histamine) into the blood stream, causing anaphylaxis.
The chemicals released from the cells cause the signs and symptoms typical of anaphylaxis. (See 'Anaphylaxis symptoms' above.) The allergic reaction can be so strong that it becomes life-threatening; for example, sudden severe swelling in the throat can lead to suffocation.
In some people with anaphylaxis, the reaction is caused by a process that does not involve allergens and IgE. However, the symptoms and treatment are the same.
ANAPHYLAXIS RISK FACTORS
Some people are more likely than others to experience anaphylaxis or to develop severe symptoms during anaphylaxis, for example, those who have one or more of the following:
ANAPHYLAXIS DIAGNOSIS
The diagnosis of anaphylaxis is based upon symptoms that occur suddenly after being exposed to a potential trigger, such as a food, medication, or insect sting.
Is it anaphylaxis or another problem? — A number of other heath problems can cause symptoms that are similar to those of anaphylaxis. These include a severe asthma attack, a heart attack, a panic attack, or even food poisoning. Evaluation by a specialist can help to clarify the diagnosis.
Tryptase is a protein that is released into the blood during an anaphylactic reaction. An increased amount of tryptase can sometimes be measured in a blood sample collected during the first three hours after anaphylaxis symptoms have begun. Unfortunately, tryptase levels are normal in many people with anaphylactic reactions. For example, it is seldom elevated in food-induced anaphylaxis.
ANAPHYLAXIS TREATMENT
The treatment and prevention of anaphylaxis are discussed separately. (See "Patient information: Anaphylaxis treatment and prevention".)
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed every four months on our web site (www.uptodate.com/patients).
Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient Level Information:
Patient information: Anaphylaxis treatment and prevention
Patient information: Use of an epinephrine autoinjector
Professional Level Information:
Anaphylaxis: Rapid recognition and treatment
Bee, yellowjacket, wasp, and other Hymenoptera stings: Reaction types and acute management
Clinical manifestations of food allergy: An overview
Diagnosis of Hymenoptera venom allergy
Diagnostic tools for food allergy
Differential diagnosis of anaphylaxis in children and adults
Drug eruptions
Fatal anaphylaxis
Food-induced anaphylaxis
History and physical examination in the patient with possible food allergy
Immediate hypersensitivity reactions to radiocontrast media
Laboratory tests to support the clinical diagnosis of anaphylaxis
Pathophysiology of anaphylaxis
The following organizations also provide reliable health information.
(www.aaaai.org/patients/gallery/anaphylaxis.asp)
(www.foodallergy.org/anaphylaxis/index.html)
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UpToDate performs a continuous review of over 440 journals and other resources. Updates are added as important new information is published. The literature review for version 19.1 is current through Mon Jan 31 00:00:00 GMT 2011; this topic was last changed on Mon Jun 02 00:00:00 GMT 2008. The next version of UpToDate (19.2) will be released in Sun Jul 31 00:00:00 GMT 2011.