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

Sample
- A venous blood sample is needed to get the serum.
- A random sample can be used.
- Analyze a fresh sample or store at 4 °C for less than 72 hours.
- Avoid lipemic or hemolyzed samples.
Purpose of the test (Indications)
- It is done to diagnose an allergy.
- This is a blood test and different than the skin test.
- It is indicated in patients where skin test is contraindicated.
Contraindication
- If the patient has a reaction to the skin test for allergy.
- If patients have multiple sources of allergens.
Pathophysiology
- This is a type 1 hypersensitivity reaction where there is the role of IgE type of antibody.
- Where allergen (Antigen) produces IgE type of antibody.
- Mast cells and Basophils have a receptor for the Fc portion of IgE.
- 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 :
-
- Animal dandruff.
- Foods.
- Pollens.
- Dust.
- Molds.
- Insect venoms.
- Drugs.
- 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:
- Asthma.
- Dermatitis.
- Food allergy.
- Drug allergy.
- Occupational allergy.
- Latex allergy.
- Angioedema.
- allergic rhinitis.
False Results may be seen in:
- If patients have a disease where there is an elevated level of IgE.
- Corticosteroids increase the level of IgE.