IgE Antibody level, Allergy Blood testing, Radioallergosorbent Test (RAST)

Sample

1. A venous blood sample is needed to get the serum.
2. A random sample can be used.
3. Analyze a fresh sample or store at 4 °C for less than 72 hours.
4. Avoid lipemic or hemolyzed samples.

Purpose of the test (Indications)

1. It is done to diagnose an allergy.
2. This is a blood test and different than the skin test.
3. It is indicated in patients where skin test is contraindicated.

Contraindication

1. If the patient has a reaction to the skin test for allergy.
2. If patients have multiple sources of allergens.

Pathophysiology

1. This is a type 1 hypersensitivity reaction where there is the role of IgE type of antibody.
2. Where allergen (Antigen) produces IgE type of antibody.
3. Mast cells and Basophils have a receptor for the Fc portion of IgE.

4. When IgE molecules form a bond over the surface of the mast cell or basophils, it leads to the release of histamine and histamine-like substances.

Stimulant for Type 1 Hypersensitivity reaction:

Various substances can give rise to this Type 1 reaction like :

• 1. Animal dandruff.
  2. Foods.
  3. Pollens.
  4. Dust.
  5. Molds.
  6. Insect venoms.
  7. Drugs.
  8. Environmental pollution.
• The total level of raised IgE is the diagnostic of an allergic reaction.
• This can be used to diagnose allergen because of the preparation of liquid allergen preparations available.

Normal IgE Level

Source 1

Age	IU/mL
Cord blood	At term ∼ 1% of the maternal value
Child
0 to 4 days	<1,5
5 days to 12 months	<15
1 to 5 years	<60
6 to 9 years	<90
10 to 16 years	<200
>16 years	<100
Adult	3 to 423
Median level	39

• To convert into SI unit x 1.0 = kIU/L

Source 2
Child

• 0 to 23 months = 0 to 13 IU /mL.
• 2 to 5 years = 0 to 56 IU/mL (<60 IU/mL)
• 6 to 10 years = 0 to 85 IU/mL (<90 IU/mL)

Adult = 0 to 100 IU/mL (<100 IU/mL)

 RAST rating with specific IgE level: 

RAST Rating	IgE level	Comments
0	< 0.35	Absent or undetectable allergen-specific IgE
1	0.35 – 0.69	Low-level allergen-specific IgE
2	0.70 – 3.49	Moderate level of allergen-specific IgE
3	3.50 – 17.49	High level of allergen-specific IgE
4	17.50 – 49.99	High level of allergen-specific IgE
5	50.00 – 100.00	Very high level of allergen-specific IgE
6	> 100.00	Extremely high level of allergen-specific IgE

Significant raised level will be seen in allergic diseases:

1. Asthma.
2. Dermatitis.
3. Food allergy.
4. Drug allergy.
5. Occupational allergy.
6. Latex allergy.
7. Angioedema.
8. allergic rhinitis.

False Results may be seen in:

1. If patients have a disease where there is an elevated level of IgE.
2. Corticosteroids increase the level of IgE.

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