Intradermal Allergy Skin Testing Concentration
For intradermal allergy skin testing, use 1/100 (1%) to 1/1000 (0.1%) of the prick testing concentration, depending on the specific allergen and clinical context. 1, 2
Standard Dilution Protocol
The typical approach follows a sequential dilution strategy:
- Start with prick/puncture testing at full strength (undiluted or standard concentration) 1
- If prick testing is negative, proceed to intradermal testing at diluted concentrations 1, 3
- Common intradermal dilutions range from 1:10 to 1:1000 of the prick test concentration 2, 4
Specific Examples from Guidelines
Drug Allergy Testing
- Corticosteroids: Use 10% concentration for skin prick tests, then dilutions of 1:1000,1:100, and 1:10 for sequential intradermal testing 2
- Penicillin: Full-strength reagents (Pre-Pen at 6 × 10⁻⁵ mol/L and penicillin G at 10,000 units/mL) are applied by prick technique first; if negative, proceed to intradermal testing at the same concentrations 1
- Omalizumab: A nonirritating concentration for intradermal testing is 1:100,000 volume-to-volume dilution (1.25 mcg/mL) 1
General Allergen Testing
- Intradermal injections use 0.01-0.02 mL (or up to 0.04-0.05 mL in some protocols) to create a 3-5 mm baseline wheal 1, 5, 4
- Sequential dilutions (10⁻⁴, 10⁻³, 10⁻², 10⁻¹) may be used for certain drugs when performing intradermal tests 4
Critical Safety Considerations
Intradermal testing is more sensitive but less specific than prick testing, with higher risk of false positives and systemic reactions 1, 5:
- Systemic reactions occur in 3.2% of intradermal tests versus 0.4% for prick tests 6
- Always perform prick testing first before proceeding to intradermal testing to minimize risk 1
- Use appropriate positive (histamine) and negative (saline) controls to validate results 1, 3
Reading and Interpretation
- Read results at 15-20 minutes for immediate reactions 1, 3
- A positive test is defined as a wheal ≥3 mm greater than negative control with a flare ≥5 mm 1, 7
- Also read at delayed timepoints (D1, D2, D4, and 1 week) for certain drug reactions 4
Important Caveats
Do not perform intradermal testing without preceding negative prick tests, as this significantly increases the risk of severe systemic reactions, particularly in asthmatic patients 1. The one exception is when prick testing cannot be performed due to skin conditions like severe eczema or dermatographism 1, 3.