Summary Allergy testing and diagnosis

Allergy Testing and Diagnosis

RAST Test

 Measures IgE levels after exposure to allergen
 Very high false positive rate (50% of IgE inhalants and 40-80% for peanut
extracts)
 Can be anaphylactic to brazil nuts but have negative IgE test
 Positive IgE test doesn’t mean the patient will ever have a reaction

Allergy Skin Prick/Scratch Test/Intradermal Allergy Test

 Small amount of allergen introduced under the skin
 Positive will have vasodilation and oedema as mast cells react
 Symptoms – redness, itchiness and swelling

Histamine

 Synthesis – decarboxylation of His by Histidine decarboxylase
 Stored at sight of synthesis
 Concentrated in lungs, GIT and skin
 IgE-R:
 Type 1 – targets mast cells and basophils, high IgE affinity and mediated by
histamine, leukotrienes, bradykinin and prostaglandins
 Type 2 – targets lymphocytes, platelets, eosinophils and monocytes, low affinity
for IgE and mediated by chemokines, IgE binding factor, mitogens and
inflammatory mediators
 Histamine Receptors:
 H1, H2, H3 and H4
 All GPCRs
 H1 – smooth muscle contraction, vasodilation, increased vascular permeability
and increased secretion
 H2 – stimulate GI secretion and cardiac stimulation
 H3 – CNS effects




 Inhibitors:
 Release inhibitors – mast cell stabilisers (Cromolyn and Nedocromil) and beta 2
agonists
 Histamine receptor antagonists