Skip to Main Content

Table Graphic Jump Location
Favorite Table | Download (.pdf) | Print




I: Anaphylactic or immediate hypersensitivity

IgE-mediated mast cell degranulation and activation

Anaphylaxis, allergic rhinitis, allergic asthma, acute urticaria, insect sting allergy

II: Antibody-mediated cytolytic reactions

IgM or IgG against antigens bound to cell membrane structures

Autoimmune or drug-induced hemolytic anemia, Goodpasture's disease, Rh hemolytic disease

III: Immune- complex mediated

Complexes of IgM or IgG and circulating antigens

Serum sickness, SLE, vasculitis, poststreptococcal glomerulonephritis

IV: Delayed hypersensitivity

T lymphocytes

Tuberculin skin test reactions, GVHD, contact dermatitis


Allergy Testing


  • Immediate hypersensitivity skin test (IHST): Stop antihistamines for 5 days before testing. Use the prick technique (introduce antigen intracutaneously via pricking or puncturing). Positive predictive value is good for inhalants, moderate for foods (high rate of false-positive results); negative predictive value is excellent for foods and inhalants.
  • Serum tests: Serum eosinophilia is often present (low diagnostic value); serum IgE is often elevated with atopic dermatitis (low diagnostic value); serum allergen-specific IgE assays (eg, RAST) measure circulating Ag-specific IgE and have similar predictive value to skin testing.




  • Definition: A serious allergic reaction that is rapid in onset and may cause death
  • Differential Diagnosis:
    • Vasovagal syncope, panic attack, hyperventilation, systemic mastocytosis, scombroid fish poisoning. Rare causes include carcinoid syndrome, pheochromocytoma, and idiosyncratic causes.
    • Anaphylactoid reactions, which have complement activation, but are not IgE mediated.
    • Example: Radiocontrast media, drugs (NSAIDS, opiate), blood products, exercise induced, and idiopathic. Clinical presentation and treatment are the same as for anaphylaxis.
  • Major Trigger: Food (most commonly peanut, tree nuts, shellfish, fish, eggs, milk), insect venom, latex, drugs, immunotherapy
  • Pathophysiology: Production of IgE in a susceptible individual (sensitization)→ IgE-sensitized mast cells and basophils→ exposure of allergen and then allergen binding leads to mast cell degranulation.
  • Clinical Symptoms and PE
    • Variable symptoms: Angioedema, shortness of breath, wheezing, flushing, urticaria, pruritus, hypotension, chest pain, syncope, abdominal pain, vomiting, diarrhea, aura of impending doom.
    • Time pattern: Uniphasic, biphasic (recur up to 8 h later in 3%–20%), or protracted syndrome.
  • Diagnostic Studies
    • Markers of mast cell degranulation, including plasma histamine (only elevated for 1 h after the onset of symptoms), urinary histamine and metabolites (elevated for longer), or serum tryptase level (peaks is 90 minutes and stays elevated for as long as 5 h) may be useful when the diagnosis is uncertain. Undetectable levels do not rule out anaphylaxis (tryptase is positive <50%).
    • In vitro allergen-specific IgE assays or IHST may be used later to confirm. IHST may not be reliably positive in sensitized individuals for up to 4 to 6 weeks after an episode of anaphylaxis. In sensitized individuals, the test should be repeated if results are negative.
  • Treatment
    • Monitor patients with mild reactions limited to flushing, urticaria, angioedema, and mild bronchospasm in the ED for a minimum of 6 to 8 hours. Consider longer observation of patients with mild symptoms who have received epinephrine because epinephrine may have minimized the symptoms.
    • Provide ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.


About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessPediatrics Full Site: One-Year Subscription

Connect to the full suite of AccessPediatrics content and resources including 20+ textbooks such as Rudolph’s Pediatrics and The Pediatric Practice series, high-quality procedural videos, images, and animations, interactive board review, an integrated pediatric drug database, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessPediatrics

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.