When any one of the following three occurs within minutes or hours of exposure to an allergen there is a high likelihood of anaphylaxis:
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 allergenSkin 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 persons 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 anaphylaxis 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 anaphylaxis. Anaphylactic shock is associated with systemic vasodilation that causes low blood pressure which is by definition 30% lower than the persons baseline or below standard values. Biphasic anaphylaxis 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.
Corticosteroids are unlikely to make a difference in the current episode of anaphylaxis, but may be used in the hope of decreasing the risk of biphasic anaphylaxis. Their prophylactic effectiveness in these situations is uncertain. Nebulized salbutamol may be effective for bronchospasm that does not resolve with epinephrine. Methylene blue has been used in those not responsive to other measures due to its presumed effect of relaxing smooth muscle. Preparedness
People prone to anaphylaxis are advised to have an allergy action plan. Parents are advised to inform schools of their childrens allergies and what to do in case of an anaphylactic emergency. The action plan usually includes use of epinephrine autoinjectors, the recommendation to wear a medical alert bracelet, and counseling on avoidance of triggers. Immunotherapy is available for certain triggers to prevent future episodes of anaphylaxis. A multi-year course of subcutaneous desensitization has been found effective against stinging insects, while oral desensitization is effective for many foods. Prognosis
In those in whom the cause is known and prompt treatment is available, the prognosis is good. Even if the cause is unknown, if appropriate preventive medication is available, the prognosis is generally good. If death occurs, it is usually due to either respiratory (typically asphyxia) or cardiovascular causes (shock), with 0.7–20% of cases causing death. There have been cases of death occurring within minutes. Outcomes in those with exercise-induced anaphylaxis are typically good, with fewer and less severe episodes as people get older.