Allergy Testing

Question 1

What is the most commonly used test that is easy to perform and is inexpensive?

Answer 1

Skin prick test.

Question 2

What is the skin prick test useful for?

Answer 2

Food allergies and pollen

Question 3

Describe the process involved in the skin prick test.

Answer 3

Drops of diluted allergen are placed on the skin after which the skin is pierced using a needle. A large number of allergens can be tested in one session. Normally includes a histamine (positive) and sterile water (negative) control. A wheal will typically develop if a patient has an allergy. Can be interpreted after 15 minutes

Question 4

What is a RAST (Radioallergosorbent test) useful for?

Answer 4

Food allergies, inhaled allergens (e.g. Pollen) and wasp/bee venom

Question 5

When would you use a RAST test over a skin prick test?

Answer 5

When skin prick tests aren’t suitable.

(e.g. extensive eczema or the patient is taking antihistamines)

Question 6

What are you looking for in a RAST test and how do you interpret it?

Answer 6

You are looking for the amount of IgE that reacts with a suspected allergen. (e.g. IgE to egg protein).

Results are given in grades 0 (negative) to 6(strongly positive)

Question 7

What is skin patch testing useful for?

Answer 7

Contact dermatitis

Question 8

Describe the skin patch testing process.

Answer 8

Around 30-40 allergens are placed on the back.

Irritants may also be tested for.

The patches are removed 48 hours later with the results being read by a dermatologist after a further 48 hours

Question 9

After how many hours can skin prick tests be read compared to skin patch tests?

Answer 9

Skin prick testing can be read after 15-20 minutes.

Skin patch testing is read 48 hours after patch removal.