Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content ++Table Graphic Jump Location|Download (.pdf)|PrintTypeMechanismExamplesI: Anaphylactic or immediate hypersensitivityIgE-mediated mast cell degranulation and activationAnaphylaxis, allergic rhinitis, allergic asthma, acute urticaria, insect sting allergyII: Antibody-mediated cytolytic reactionsIgM or IgG against antigens bound to cell membrane structuresAutoimmune or drug-induced hemolytic anemia, Goodpasture's disease, Rh hemolytic diseaseIII: Immune- complex mediatedComplexes of IgM or IgG and circulating antigensSerum sickness, SLE, vasculitis, poststreptococcal glomerulonephritisIV: Delayed hypersensitivityT lymphocytesTuberculin 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. +++ Anaphylaxis ++ Definition: A serious allergic reaction that is rapid in onset and may cause deathDifferential 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, immunotherapyPathophysiology: 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 PEVariable 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 StudiesMarkers 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.TreatmentMonitor 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.... Your Access profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth