Allergy Tests

Question 1

Food allergy: Tests

Answer 1

• 1st line: Skin prick test
• 2nd line: RAST (Radioallergosorbent test)

Question 2

Pollen allergy: Tests

Answer 2

• 1st line: Skin prick test
• 2nd line: RAST (Radioallergosorbent test)

Question 3

Wasp/bee venom allergy: Tests

Answer 3

• 1st line: Skin prick test
• 2nd line: RAST (Radioallergosorbent test)

Question 4

Contact dermatitis: Tests

Answer 4

Skin patch testing

Question 5

Peanut allergy: Tests

Answer 5

• 1st line: Skin prick test
• 2nd line: RAST (Radioallergosorbent test)

Question 6

Latex allergy: Tests

Answer 6

• 1st line: Skin prick test
• 2nd line: RAST (Radioallergosorbent test)

Question 7

Interpretation time of different allergy tests

Answer 7

• Skin prick test: 15minutes
• RAST: Few days to 2weeks
• Skin patch test: 48hours

Question 8

What is highly specific and strong predictor in case of food allergy?

Answer 8

Wheal size

Question 9

Why is RAST used as 2nd line for allergy (food, peanut, bee venom, wasp, pollen, latex)?

Answer 9

Because, RAST can be negative sometimes

Question 10

When can RAST be used as 1st line for allergy (food, peanut, bee venom, wasp, pollen, latex)?

Answer 10

When skin prick test is NOT suitable:

• Extensive eczema
• the patient is taking anti-histamines

Question 11

Why don’t we do skin prick test if patient is taking anti-histamine?

Answer 11

Chances of false negative

Question 12

Why don’t we do skin prick test if patient has extensive eczema on skin?

Answer 12

• Chances of false positive
• Less amount of skin to be pricked

Question 13

Irritants of any kind: Tests

Answer 13

Skin patch test

Question 14

Skin patch test: amoung of allergens to be placed

Answer 14

Around 30-40 allergens

Question 15

Most commonly used allergy test

Answer 15

Skin prick test

Question 16

Why is skin prick test most commonly used?

Answer 16

• Easy to perform
• Inexpensive

Question 17

Skin prick test: procedure/steps

Answer 17

• Drops of diluted allergen are placed on the skin >>> after which, skin is pierced using a needle
• Normally contains histamine (positive) control and sterile water (negative) control
• Results are interpreted after 15mins
• If wheals develop >>> positive skin prick test (presense of allergy)
• (A large number of allergen can be tested in one session)

Question 18

RAST (radioallergosorbent): Procedure/steps

Answer 18

• Determine a suspected allergen (known allergen) e.g. IgE to egg protein
• Blood test to know the amount of IgE that reacts specifically to that allergen
• Grade “Amount of IgE” in 0 to 6
• Interpretation: 0 = negative; 6 = strongly positive

Question 19

Skin patch test: Procedure/steps

Answer 19

Around 30-40 allergens or irritants are placed on the back >>> after 48huors, a dermatologist interpret the result

Question 20

Wheal size is interpreted in- ?

Amount to specified IgE in blood is interpreted in- ?

Answer 20

• Wheal size is interpreted in Skin prick test
• Amount of IgE is interpreted in RAST (radioallergosorbent test)