Key Points
- Gold standard for identifying IgE-mediated allergic responses
- Provides immediate results within 15-20 minutes
- Suitable for children over 6 months of age
- Tests multiple allergens simultaneously
- High sensitivity and specificity when performed correctly
Clinical Indications
- Suspected food allergies
- Environmental allergies
- Allergic rhinitis
- Atopic dermatitis
- Drug allergies
- Insect sting allergies
Types of Allergy Skin Tests
1. Skin Prick Test (SPT)
- Most common first-line test
- Tests immediate hypersensitivity
- Results available in 15-20 minutes
- Multiple allergens tested simultaneously
2. Intradermal Test
- More sensitive than SPT
- Used when SPT is negative but strong suspicion exists
- Higher risk of systemic reactions
- Not recommended for food allergies
3. Skin Patch Test
- Tests delayed hypersensitivity reactions
- Applied for 48 hours
- Results read at 48 and 72-96 hours
- Useful for contact dermatitis
Procedure Steps
Preparation
- Obtain detailed medical history
- Document current medications
- Discontinue antihistamines 5-7 days prior
- Clean test area (usually back or forearm)
- Mark and label test sites
Skin Prick Test Technique
- Apply drops of allergen extracts
- Prick through drops using sterile lancet
- Include positive (histamine) and negative (saline) controls
- Wait 15-20 minutes
- Measure wheal and flare response
Equipment Required
- Allergen extracts
- Sterile lancets
- Positive and negative controls
- Measuring ruler
- Emergency medications
- Documentation materials
Result Interpretation
Positive Result Criteria
- Wheal ≥3mm larger than negative control
- Flare ≥10mm in diameter
- Positive control must show expected reaction
Documentation Requirements
- Size of wheal and flare for each allergen
- Time of reading
- Presence of pseudopods
- Patient symptoms during testing
- Photographs if indicated
Result Significance
- Larger wheal size suggests stronger sensitivity
- Clinical correlation required
- False positives and negatives possible
- Consider specific IgE testing for confirmation
Precautions and Contraindications
Absolute Contraindications
- Severe uncontrolled asthma
- Active anaphylaxis
- Severe dermatographism
- Active skin condition at test site
Relative Contraindications
- Age less than 6 months
- Pregnancy
- Beta-blocker use
- Recent severe allergic reaction
Required Safety Measures
- Emergency medications available
- Trained staff present
- Post-test observation period
- Written emergency protocols
Further Reading
