Diagnostic and Lab Tests

Question 1

RAST (Radioallergosorbent test)

Answer 1

(aka allergen SPECIFIC IgE antibody) Blood test that is used to determine specific items a pt is allergic to. (if a pt is allergic to pollen, they will have a high level of IgE for pollen).

Question 2

Benefits of RAST

Answer 2

1. more specific than skin testing
2. not affected by skin reactivity
3. pts do not have to stop drugs (i.e. antihistamines/betablockers)

Question 3

What types of allergies can you test with RAST

Answer 3

Food and environmental

Question 4

Levels of RAST

Answer 4

3.5-18 high IgE
18-50 Very high
50-100 ultra high
>100 extremely high

Question 5

Eosinophil count

Answer 5

Blood test that measures the # of eosinophils. Usually confirms a diagnosis, not making one.

Question 6

What is a normal eosinophil count

Answer 6

Taken from a CBC differential. Count of more than 500/microliters is considered abnormal

Question 7

What can eosinophil counts help diagnose

Answer 7

1. Atopic dermatitis
2. Asthma
3. Seasonal allergies
4. Parasites
5. Autoimmune disease

Question 8

Eosinophil smear

Answer 8

Can be nasal or urine smears. Testing to see if there is a presence of eosinophils in the cx.

Question 9

Uses of eosinophil smears

Answer 9

Allergic rhinitis and atopic conditions, or parasitic infections

Question 10

Serum immunoglobulin E (IgE) levels

Answer 10

Also called total IgE. This is a blood test that monitors the total level of IgE in the body. But it can be elevated even in non allergic conditions, so there may be some some false positives associated with it. Often times order with an allergen specific IgE test (RAST)

Question 11

What types of allergies can IgE levels be tested on

Answer 11

1. Asthma
2. Atopic diseases
3. Food
4. Environmental
   Not diagnostic for a specific allergy, just lets you know that there is potential for allergy if elevated

Question 12

Reference range of IgE

Answer 12

Dependent on age, sex, other diseases but the general range is 30-700 KU/L

Question 13

Skin patch (or prick testing)

Answer 13

Can be skin prick testing, intradermal testing or patch. Allergen is placed on forearm or back and enters the sub epithelial layer. This is where mast cells reside.

Question 14

Types of allergies that skin patch or prick testing is used on

Answer 14

1. Food
2. Environmental
3. Atopy

Question 15

Which test is the gold standard for allergic rhinitis

Answer 15

skin prick test (more sensitive than a RAST)

Question 16

Which test is the gold standard for food allergies

Answer 16

oral food challenge

Question 17

What is a disadvantage of SPT

Answer 17

Must stop antihistamines

Question 18

Oral food challenge

Answer 18

Method used to detect food allergies. It is done in clinic by feeding the pt increasingly large portions of suspected food

Question 19

Interpretation of oral food challenge

Answer 19

Presence of symptoms may indicate allergy to a particular food

Question 20

Trial elimination diet

Answer 20

Method to detect IgE mediated food allergies. Food is eliminated for 2-4 weeks

Question 21

Interpretation of elimination diet

Answer 21

If symptoms go away you have found your allergen