Blood Test for Allergies

Blood tests are helpful for identifying allergies to foods, medicines, insect stings, mold, pollen, pet dander, and dust mites.

Blood tests measure the immunoglobulin E (IgE) antibody levels in the blood, which are elevated after an allergic reaction. Generally speaking, there are 2 types of blood tests: total IgE and specific IgE.

Total IgE blood testing indicates if an allergic reaction occurred but will not be able to distinguish the specific allergen. A specific IgE test, on the other hand, measures IgE antibody levels in response to individual allergens.

Blood tests are used when skin testing may cause problems. For example, blood tests are conducted when:

• The patient’s skin is easily irritated as a result of a severe skin condition such as psoriasis or eczema.
• A skin test is too risky to conduct due to medication that interferes with skin testing, and the patient’s medicine cannot be stopped temporarily.
• Testing with a strong allergen may cause an overwhelmingly positive reaction that results in anaphylaxis.
• A skin test must be verified due to a suspected false positive or false negative. For instance, patients who may have a food allergy to crustacean seafood (shrimp, crab, lobster, etc.) may get a false positive skin test. This is due to sensitization to dust mites, spiders, and cockroaches, which are closely related to crustaceans.

Unlike skin tests, blood tests only require a single needle prick. Patients who are on medication can continue to stay on their medicine without it interfering with allergy testing. However, blood results take some time to receive and depending on the test, there may still be false positives. Additionally, blood tests typically cost more than skin tests.