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What are the 3 criteria for anaphylaxis?

Anaphylaxis is a severe, potentially life-threatening allergic reaction. It can occur within seconds or minutes of exposure to something a person is allergic to, such as food, insect stings, medication, or latex. Anaphylaxis requires immediate medical treatment as it can quickly become fatal if not treated right away.

Criteria for Diagnosing Anaphylaxis

There are 3 main criteria for diagnosing anaphylaxis that were established by the National Institute of Allergy and Infectious Diseases and the Food Allergy and Anaphylaxis Network in 2006. These include:

  1. Acute onset of illness (minutes to hours) with involvement of skin, mucosal tissue, or both (e.g. generalized hives, itching or flushing, swollen lips/tongue/uvula)
  2. Respiratory compromise (e.g. dyspnea, wheeze or bronchospasm, stridor, reduced PEF, hypoxemia)
  3. Reduced blood pressure or associated symptoms of end-organ dysfunction (e.g. hypotonia, collapse, syncope, incontinence)

If any one of these 3 criteria are met, a diagnosis of anaphylaxis can be made. The more criteria that are present, the more likely the reaction is anaphylactic.

Criterion 1: Skin and Mucosal Changes

The first diagnostic criterion for anaphylaxis is acute onset of illness with skin or mucosal tissue involvement. This typically appears as:

  • Generalized hives (urticaria), itching, or flushing
  • Swollen lips, tongue, or uvula

Around 80-90% of people experiencing anaphylaxis will develop hives or angioedema. The skin changes appear rapidly, often within minutes of exposure. The welts and swelling are caused by the sudden release of inflammatory chemicals like histamine from mast cells in the skin.

Criterion 2: Respiratory Compromise

The second diagnostic criterion for anaphylaxis is respiratory compromise and symptoms such as:

  • Wheezing or bronchospasm
  • Stridor
  • Reduced peak expiratory flow
  • Hypoxemia (low oxygen levels)
  • Dyspnea (shortness of breath)

Respiratory symptoms occur in up to 70% of anaphylactic episodes. Anaphylaxis causes the airways to constrict, swell, and fill with mucus, making breathing very difficult. The swelling narrows the airways while the mucus plugs them, often prompting coughing or wheezing as the person struggles to breathe.

Criterion 3: Reduced Blood Pressure

The third diagnostic criterion for anaphylaxis is a drop in blood pressure (hypotension) or associated symptoms such as:

  • Collapse
  • Syncope (fainting)
  • Incontinence

A sudden drop in blood pressure occurs in up to 35% of anaphylactic episodes. It is the most dangerous aspect of anaphylaxis and leads to shock, which can be fatal. During anaphylactic shock, the blood pressure drops suddenly and the heart is unable to pump enough blood to vital organs.

Common Symptoms and Body Systems Affected

In addition to the 3 main diagnostic criteria, anaphylaxis also commonly involves the following symptoms due to its systemic effects on the body:

  • Skin – hives, itching, warmth, swelling, flushing, rashes
  • Respiratory – coughing, wheezing, shortness of breath, throat tightness
  • Cardiovascular – lightheadedness, dizziness, arrhythmias, chest pain, fainting, shock
  • Gastrointestinal – nausea, vomiting, diarrhea, cramping pain
  • Other – anxiety, headache, uterine cramps, metallic taste

Because anaphylaxis is a full-body reaction, many different systems can be affected. The severity of symptoms can vary from mild to severe.

Triggers for Anaphylaxis

There are many possible triggers that can cause an anaphylactic reaction in susceptible people. The most common triggers include:

  • Foods – peanuts, tree nuts, shellfish, eggs, milk, wheat, soy, etc
  • Insect stings – bees, wasps, hornets, yellow jackets, fire ants
  • Medications – antibiotics, NSAIDs, chemotherapy
  • Latex
  • Exercise
  • Idiopathic (unknown cause)

Food allergies are the most common cause of anaphylaxis, especially in children. Peanuts, tree nuts, and shellfish account for most food-related anaphylactic reactions. Adults are more prone to anaphylaxis from medications or insect stings.

Risk Factors for Anaphylaxis

While anaphylaxis can happen to anyone, certain risk factors increase susceptibility:

  • Having a history of asthma, eczema, or hay fever
  • Having had a prior anaphylactic reaction
  • Being a teenager or young adult
  • Having food allergies

Asthma in particular puts a person at higher risk, as any respiratory or allergy trigger is more likely to result in anaphylaxis. A prior anaphylactic reaction also increases the chances of it occurring again in the future.

Diagnosing Anaphylaxis

Anaphylaxis is diagnosed based on the criteria described above. Taking a thorough history about symptoms and potential triggers is important. Laboratory tests are not helpful for diagnosing anaphylaxis in the moment, but may be done after to look for elevated tryptase levels.

Skin prick allergy testing or blood tests for specific IgE antibodies can help identify sensitivities to potential triggers after the reaction has resolved. This can guide avoidance measures and preparedness in case of future episodes.

Anaphylaxis Treatment and Management

Anaphylaxis is a medical emergency that requires prompt treatment with epinephrine, oxygen, fluids, antihistamines, and monitoring. Epinephrine is the first-line treatment to reverse the life-threatening breathing and blood pressure problems.

The main steps in anaphylaxis management include:

  1. Administer epinephrine via auto-injector or injection as soon as anaphylaxis is recognized.
  2. Call emergency medical services (e.g. 911) for ambulance transport to hospital.
  3. Administer oxygen, intravenous fluids, and asthma medications like inhaled bronchodilators if available.
  4. Antihistamines and steroids may help treat skin symptoms but are not first-line.
  5. Monitor breathing, airway, blood pressure, cardiac status until symptoms improve.
  6. Observe in hospital for delayed or protracted reactions.

Individuals at risk for anaphylaxis should have an epinephrine auto-injector (like EpiPen) available at all times. At the first sign of a reaction, use the epinephrine injector then seek emergency care. Epinephrine helps reverse airway constriction and improves blood pressure to prevent complications and death.

Long-Term Management

After an anaphylactic episode, long-term management should focus on trigger avoidance, being prepared with epinephrine, and immunotherapy:

  • Avoid triggers – Strict avoidance of known food, medication, or insect sting triggers.
  • Epinephrine on hand – Have injectors available and know when/how to use them.
  • Immunotherapy – Allergy shots or oral immunotherapy may desensitize some people to triggers like venoms or foods.

Wearing a medical alert bracelet can also help identify the condition to providers in case of another reaction.


In summary, the 3 main diagnostic criteria for anaphylaxis include acute illness onset with skin/mucosal changes, respiratory compromise, and reduced blood pressure/associated symptoms. Anaphylaxis requires immediate treatment with epinephrine as it can quickly become life-threatening. Long term management focuses on trigger avoidance, being prepared with epinephrine, and possible immunotherapy.