IgE Antibody level, Allergy Blood testing, Radioallergosorbent Test (RAST)
- 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.
- If the patient has a reaction to the skin test for allergy.
- If patients have multiple sources of allergens.
- 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.
- Insect venoms.
- 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
|Cord blood||At term ∼ 1% of the maternal value|
|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|
|Adult||3 to 423|
- To convert into SI unit x 1.0 = kIU/L
- 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:
- Food allergy.
- Drug allergy.
- Occupational allergy.
- Latex allergy.
- 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.