Allergy Blood Test
Whenever a person comes in contact with an allergen, an antibody is produced in response to it. An allergy test is done to detect and measure allergen-specific antibodies present in the blood. The allergy test can be in the form of
- Blood test
- Skin test
- Elimination diet
When is an allergy test prescribed?
A doctor may recommend this test
- When a patient is exposed to any allergen and has symptoms like sneezing, redness on the skin, itching, swelling on the body, stuffy nose
- To screen the most common allergy triggers, including dust, pet dander, trees, grass, weeds, molds, nuts, shellfish.
- In patients who have poorly controlled asthma, unstable heart condition.
- In skin conditions like eczema, psoriasis
- Life-threatening conditions like anaphylactic shock.
- To detect how well the allergy treatment is working.
What are the components of allergy test?
1) Allergy blood tests measure the amount of IgE antibodies in the blood produced as a response to allergens. Allergy blood tests may include-
- Enzyme-linked immunosorbent assay (ELISA, or EIA) - measures the amount of allergen-specific antibodies in the blood.
- Radio allegro sorbent test (RAST) - measures specific allergen-related antibodies to identify the allergy triggers.
- A small amount of IgE antibodies is normal.
- A larger amount of IgE may mean a patient has an allergy.
2) Allergy skin test
Done in three ways
- Scratch test: Done by marking and labeling areas on skin with a pen followed by placing a drop of a potential allergen on each of those spots. The outer layer of skin is then scratched to let in the allergen.
- Intradermal test: this is done by injecting allergen on the skin of forearm. These two tests take 5 to 10 minutes
- Patch test: an allergen is put on a patch and then stuck on the arm or back. Patch is worn for about 48 hours.
The test is positive if there is a wheal and flare response.
3) Elimination diet test
Done by avoiding certain foods or ingredients from one’s diet so that one can find out what he might be sensitive to. Done in two phases-
- The elimination phase- avoid eating suspicious foods.
Preparation and Prerequisites
- Don't take antihistamines for 3 to 7 days before the test.
- Not to eat anything which has reacted in the past.
- Avoid overexposure to sun before skin allergy test.