What is the concentration of allergy extract used in intradermal allergy skin testing and what are the guidelines for its use?

Intradermal Allergy Skin Testing Concentration

For intradermal allergy skin testing, use a 1:1000 (vol/vol) or 1:10,000 (vol/vol) dilution of the maintenance concentrate, injecting 0.02-0.05 mL into the dermis. 1

Standard Testing Protocol

• Inject 0.02-0.05 mL of allergen extract into the dermis using the appropriate dilution based on patient sensitivity 1, 2, 3
• The 1:1000 (vol/vol) dilution serves as the standard starting concentration for most patients with moderate sensitivity 1
• For highly sensitive patients—identified by clinical history or strong prick test reactivity—start with the more dilute 1:10,000 (vol/vol) concentration 1, 4

Concentration Selection Algorithm

Step 1: Assess Patient Sensitivity

• Review clinical history for severity of allergic symptoms and prior reactions 4
• Evaluate prick test results if already performed (strong reactions indicate need for more dilute intradermal testing) 4

Step 2: Choose Initial Dilution

• Standard sensitivity patients: Begin with 1:1000 (vol/vol) dilution 1, 4
• Highly sensitive patients: Begin with 1:10,000 (vol/vol) dilution 1, 4
• This represents a 10-fold or 10,000-fold dilution from the maintenance concentrate used for immunotherapy 4

Step 3: Select Extract Type

• Prioritize standardized extracts when available (cat, dust mite, grasses, ragweed, Hymenoptera venoms) because they provide consistent biologic activity and reduce risk of unexpected reactions 4, 1
• Standardized extracts are labeled in BAU (Bioequivalent Allergy Units) or AU (Allergy Units) rather than weight/volume 4
• For nonstandardized extracts, recognize that potency varies widely between manufacturers even at identical weight/volume concentrations 4, 1

Special Considerations for Specific Allergens

Hymenoptera Venom Testing:

• A positive intradermal response at ≤1.0 µg/mL concentration confirms specific IgE antibodies 4
• This is a critical threshold for determining need for venom immunotherapy 4

Fire Ant Testing:

• Use whole-body extract (no venom extract commercially available) 4
• Positive intradermal test is defined as reaction at 1:1000 wt/vol or less 4

Critical Safety Guidelines

Avoid These Common Pitfalls:

• Never assume equivalent potency between different manufacturers' nonstandardized extracts at the same labeled concentration—biologic activity can vary dramatically 4, 1
• Do not perform intradermal testing without emergency equipment immediately available, as anaphylaxis can occur even with diagnostic testing 1
• Do not increase concentration if the patient is experiencing symptom exacerbation or during peak allergen exposure season, as systemic reaction risk increases 4

Dilution Stability:

• Short ragweed at 1:10 vol/vol dilution remains stable for 12 months in all storage conditions 4
• Dust mite and cat at 1:10 and 1:100 vol/vol dilutions remain stable for 12 months 4
• The expiration date of any dilution cannot exceed the earliest expiring constituent in the mixture 4

Interpretation Context

• Intradermal testing is more sensitive but less specific than prick testing 2, 3
• A positive intradermal test must be correlated with clinical symptoms to confirm true allergy, as sensitization (positive test) does not always equal clinical disease 2, 3
• Intradermal testing is typically performed when prick tests are negative or equivocal but clinical suspicion remains high 2, 3