Type of test : Blood

Normal findings : Total IgE serum

Adult: 0-100 international units/mL

Child: 0-23 months: 0-13 international units/Ml

 2-5 years: 0-56 international units/mL

 6-10 years: 0-85 international units/mL

 Test explanation and related physiology

Measurement of serum IgE is an effective method to diagnose allergy and specifically identify the allergen (the substance to which the person is allergic). Serum IgE levels increase when allergic individuals are exposed to the allergen. Various classes of allergens can initiate the allergic response.

Although skin testing can also identify a specific allergen, measurement of serum levels of IgE is helpful when a skin test result is questionable, when the allergen is not available in a form for dermal injection, or when the allergen may incite an ana phylactic reaction if injected. IgE is particularly helpful in cases in which skin testing is difficult (e.g., in infants or in patients with dermatographism or widespread dermatitis), and it is not always necessary to remove the patient from antihistamines, ACE inhibitors, antidepressants, or beta-blockers. The decision as to which method to use to diagnose an allergy and to identify the allergen depends on the elapsed time between exposure to an allergen and testing, class of allergen, the age of the patient, the possibility of anaphylaxis, and the affected target organ (e.g., skin, lungs, or intestine). In general, allergy skin testing is the preferred method in comparison with various in vitro tests for assessing the presence of specific IgE antibodies because it is more sensitive and specific, simpler to use, and less expensive.

IgE levels, similar to provocative skin testing, are used not only to diagnose allergy but also to identify the allergen so that an immunotherapeutic regimen can be developed. Increased levels of total IgE can be diagnostic of allergic disease in general. Specific IgE blood allergy testing, however, is an in vitro test for specific IgE directed to a specific allergen. Since the development of liquid allergen preparations, the use of in vitro blood allergy testing has increased considerably. It is more accurate and safer than skin testing. Allergy testing of IgG antibodies can also be performed and may provide a more accurate correlation between allergen and allergic symptoms. Similar to IgE antibody testing, IgG antibody testing is often performed in “panels.” For example, there are meat panels that might include IgE or IgG testing for chicken, duck, goose, and turkey. Testing a fruit panel might include IgE or IgG antibody testing for apples, bananas, peaches, and pears. Testing in panels diminishes the cost of testing. Specific allergen antibody testing can follow panel testing.

Contraindications

• Patients with multiple allergies; no information will be obtained regarding identification of the specific allergen.

 Interfering factors

 • Concurrent diseases associated with elevated IgG levels will cause false-negative results.

Procedure and patient care

 • See inside front cover for Routine Blood Testing.

 • Fasting: no

 • Blood tube commonly used: serum separator

* Inform the patient that the suspected allergen will be mixed with the patient’s blood specimen in the laboratory. The patient will not experience any allergic reaction by this method of testing.

• Determine whether the patient has recently been treated with a corticosteroid for allergies.

Abnormal findings

 Allergy-related diseases

 Asthma

 Dermatitis

 Food allergy

 Drug allergy

 Occupational allergy

 Allergic rhinitis

 Angioedema