II. Mechanism: Assays
- RadioAllergoSorbent Test (RAST)
- Older methodology
- ImmunoCAP has largely replaced the older RAST methodology
- Enzyme-linked Immunosorbent Assay (ELISA, most common)
- Fluorescent Enzyme Immunoassay (FIA)
- Chemiluminescent Immunoassay
III. Efficacy
- Lower Test Sensitivity than allergy Skin Testing
- Highly specific for allergens
- Standardized testing to 95% Positive Predictive Value for reactivity within the testing population
- Contrast with Skin Testing extracts which are not standardized
- Positive Result Precautions
- Positive tests do not absolutely indicate allergy
- Level of specific IgE does not correlate with severity of allergy
- Negative Result Precautions
- Negative results may indicate lack of prior exposure (and not lack of allergy risk)
IV. Indications
- Not recommended for food, venom, or drug allergies unless high risk for Anaphylaxis
- Alternative to Skin Testing in certain cases
- Age <3 years
- Skin Testing contraindicated
- High risk for Anaphylaxis
- Uncontrolled Asthma or other medical conditions
- Essential medications that require continuation (e.g. Beta Blockers, Antihistamines)
- Skin conditions that interfere with Skin Testing (e.g. Eczema)
-
Allergy Testing for common allergens
- Pet dander
- Dust mites
- Pollen
- Mold spores
V. Approach: Screen Contents
- June Grass and cross reacting grasses
- Rye
- Sweet Vernal
- Timothy
- Brome
- Oak Tree
- Short ragweed
- Alternaria mold
- Dust mite
- Cat
VI. Technique
VII. Interpretation: RAST Scoring
- Class 0: 200-750 (No significant allergy)
- Class 1: 750-1600 (Mild allergy)
- Class 2: 1600-3600 (Moderate allergy)
- Class 3: 3601-8000
- Class 4: 8001-18000
- Class 5: 18001-40000 (Most allergic)