II. Indications
- Allergic response to inhalants, food, Insect Bites or medications
III. Mechanism
- IgE mediated, immediate-type Hypersensitivity
IV. Contraindications
- Severe Eczematous Dermatitis
- Dermatographism
- History of Anaphylaxis
- Very young
- Unable to discontinue Antihistamines
- Uncontrolled Asthma (Peak Expiratory Flow < 75%)
V. Preparation
- Have Epinephrine and Albuterol available
- Discontinue Antihistamines before testing
- Second Generation Antihistamines: 2 weeks before test
- First Generation Antihistamines: 3 days prior to test
- Other Antihistamine-type agents to stop before test
- Phenothiazine
- Tricyclic Antidepressants
- Anticholinergic Medications
- H2 Receptor blocking medications (e.g. Ranitidine)
- Inhaled Corticosteroids do not affect test
- Short-term Systemic Corticosteroids do not affect test
VI. Technique
- Test 6-10 Antigens to determine presence of IgE disease
-
Antigen exposure techniques
- Prick method
- Scratch method
- Intradermal (injected)
- Most accurate
- Used in cases requiring higher Test Sensitivity (e.g. Insect sting allergy, Penicillin Allergy)
- Use Controls
- Positive Control: Histamine
- Negative Control: Glycerol-Saline
- Read test 15 minutes after application of allergen
- Positive if wheal diameter 3 mm > negative control
- Use Regional Allergy Screening guidelines
- Relies on cross reactivity among Antigen groups
- Tree
- Grass
- Weed
- Mold
- House Dust mite
- Cat
VII. Interpretation
- All Tests negative: No further testing needed
- One or more inhalants positive: Complete regional panel
-
Dust mite only positive: No further testing needed
- Avoid Dust mites
- Consider Immunotherapy
- Cat only positive: No further testing needed
- Avoid exposure and reduce dander
- Consider Immunotherapy
- If Positive Control is Negative
- Try RAST testing
- Patient may be on Antihistamine or steroid
- IF short acting Antihistamine
- Stop Antihistamine and retest after 2 days
- IF long acting Antihistamine
- Stop Antihistamine and retest after 3-4 weeks
- IF short acting Antihistamine
- If reaction occurs to Negative Control
- Intradermal Allergy Test Indications
- Suspected Insect Sting Allergy (e.g. bee, hornet)
- Suspected Drug Allergy (e.g. Penicillin, Anesthetic)
VIII. References
- (1999) NPI Allergy Testing Conference, Las Vegas
- Chang (2018) Am Fam Physician 98(1): 34-9 [PubMed]
- James (2002) Am Fam Physician 66(4):621-6 [PubMed]