Allergy Blood Testing is a measurement of serum Immunoglobin E (IgE). Allergy Blood Testing 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. They include animal dandruff, foods, pollens, dusts, molds, insect venoms, drugs, and agents in the occupational environment.
Although Allergy 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 anaphylactic reaction if injected into the patient. IgE is especially helpful in cases in which skin testing is particularly difficult (e.g., in infants, or in patients with dermatographism or widespread dermatitis). However, it is important to note that an assay for IgE is expensive and the results are not available immediately. The decision concerning 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, age of patient, the possibility of anaphylaxis, and the affected target organ (skin, lungs, intestine, etc.)
IgE levels, like 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.
Once the allergen has been identified, for most patients, the treatment would include avoidance of the allergen and use of bronchodilators, antihistamines, and possibly steroids. If aggressive antiallergy treatment is provided before testing, IgE levels may not rise despite the existence of an allergy.
Allergy to latex-containing products is an increasingly common allergy for which certain industrial and most medical personnel are at risk. It is an allergy that may develop in otherwise nonallergic patients because of overexposure. Furthermore, patients with latex exposure are at risk for allergic reaction if they undergo operative procedures or any procedure for which the health care personnel wear latex gloves. In these patients a latex-specific IgE can be easily identified with the use of an enzyme-labeled immunometric assay. This test is 94% accurate.
There are many methods of measuring IgE. One of the most commonly used methods is the radioallergosorbent test (RAST). In this method, the serum of a patient suspected of having a specific allergy is mixed with a specific allergen. The antibody-allergen complex is then incubated with one or more radiolabeled monoclonal anti-IgE antibodies. The total amount of IgE can be measured. Enzyme-conjugated, radioimmunometric, colorimetric, fluorometric, or chemiluminometric methods are used for allergen-specific IgE quantification. Accuracy varies between 45% and 95% depending on the allergen.
When not to Use Allergy Blood Testing?
Allergy Blood Testing cannot be used to diagnose allergies for patients with multiple allergies because no information will be obtained regarding identification of the specific allergen.
Normal Serum IgE Levels
The Normal Total Immunoglobin E Level in serum very by age. IgE levels are the lowest in infants and they increase as the person grows. The following are the Normal IgE levels for different age groups:
Children younger than 2 years of age: None or less than 14 International units/mL.
Children between 2 and 5 years: None or less than 57 International units/mL.
Children between 6 and 10 years: None or less than 86 International units/mL.
Adults: None or less than 101 International units/mL.
Causes of Allergy Blood Testing False Results
- Concurrent diseases associated with High IgG Levels (e.g. Asthma) will cause false-negative results.
- Drugs that may cause increased IgE levels include Corticosteroids.
Causes of High IgE Levels in blood
All of the following diseases are immunoreactive conditions in their pathophysiology. IgE is the mediator of the “allergic response” and can be expected to be elevated in these diseases:
- Food Allergy.
- Drug Allergy.
- Latex Allergy.
- Occupational Allergy.
- Allergic Rhinitis.