ALLERGY TESTING QUESTIONS AND
ANSWERS WITH SOLUTIONS 2024
What total IgE level is suggestive of allergic disease? - ANSWER > 100 iu/mL
How long should patients avoid antihistamines prior to skin allergy testing? - ANSWER 4 to 7 days
What are some common in vivo methods of testing for allergic sensitivity? - ANSWER 1. Prick testing. Small
amount of antigen placed in the epidermis. Wheal (raised) and flare (redness) are measured to judge
response.
2. Intradermal testing. Antigen injected intradermally (similar to PPD) and increase in starting wheal
measured. Increase from 5 mm to 7mm or greater is positive. If prior epidermal test was negative, can
start at 1:1000 dilution. Otherwise need to start lower (1:312,500) to avoid serious reaction if significant
hypersensitivity.
3. Interadermal dilutional testing. Start at 1:312,500. Serial administration of increasing concentrations at
5-fold intervals. If no reaction at 1:500, test is negative.
What are some benefits of in vitro (i.e. RAST) testing for allergic sensitivity vs. in vivo techniques?
Disadvantages? - ANSWER Advantages:
1. No exposure to antigen, so no risk of anaphylaxis.
2. Single venipuncture, so faster for the patient, easier tolerated by children.
3. Don't have to stop antihistamines.
4. Provides quantitative measurement.
Disadvantages:
1. More expensive.
2. Results not immediately available.
3. Less sensitive for some allergens, especially molds.
ANSWERS WITH SOLUTIONS 2024
What total IgE level is suggestive of allergic disease? - ANSWER > 100 iu/mL
How long should patients avoid antihistamines prior to skin allergy testing? - ANSWER 4 to 7 days
What are some common in vivo methods of testing for allergic sensitivity? - ANSWER 1. Prick testing. Small
amount of antigen placed in the epidermis. Wheal (raised) and flare (redness) are measured to judge
response.
2. Intradermal testing. Antigen injected intradermally (similar to PPD) and increase in starting wheal
measured. Increase from 5 mm to 7mm or greater is positive. If prior epidermal test was negative, can
start at 1:1000 dilution. Otherwise need to start lower (1:312,500) to avoid serious reaction if significant
hypersensitivity.
3. Interadermal dilutional testing. Start at 1:312,500. Serial administration of increasing concentrations at
5-fold intervals. If no reaction at 1:500, test is negative.
What are some benefits of in vitro (i.e. RAST) testing for allergic sensitivity vs. in vivo techniques?
Disadvantages? - ANSWER Advantages:
1. No exposure to antigen, so no risk of anaphylaxis.
2. Single venipuncture, so faster for the patient, easier tolerated by children.
3. Don't have to stop antihistamines.
4. Provides quantitative measurement.
Disadvantages:
1. More expensive.
2. Results not immediately available.
3. Less sensitive for some allergens, especially molds.
