Definition
- Allergic diseases are manifested as hyperresponsiveness in the target organ, whether the skin, nose, lung, or GI tract. Most tests for "allergy " � are actually tests for allergic sensitization, or the presence of allergen-specific IgE.
- Most patients who experience symptoms upon exposure to an allergen have demonstrable IgE that specifically recognizes that allergen, making these tests essential tools in the diagnosis of allergic disorders.
- In vitro testing for allergy has certain advantages:
- It poses no risk to the patient of an allergic reaction.
- It is not affected by medications (antihistamines, etc.) the patient may be taking.
- It is not reliant upon skin integrity or affected by skin disease.
- It can be more convenient for the patient. In vitro testing requires submitting a blood sample and does not necessitate a separate visit for skin testing.
- Clinical performance of specific IgE-based serum allergen tests typically has sensitivity ranging from 84% to 95% and specificity ranging from 85% to 94%.
- Various types of specific panels, mixes, as well as specific allergen tests currently performed at various labs and contact your lab for details.
Normal range:
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View Large kUA/L Class Level of Allergen-Specific IgE Antibody 0.35 0 Absent 0.35 " �0.69 I Low 0.70 " �3.49 II Medium 3.50 " �17.49 III High 17.5 " �49.99 IV Very high 50.0 " �100 V Very high >100 VI Very high � �
Use
- To establish the diagnosis of an allergic disease and to define the allergens responsible for eliciting signs and symptoms
- To identify allergens that may be responsible for allergic disease and/or anaphylactic episode and to confirm sensitization to particular allergens prior to beginning immunotherapy
- To investigate the specificity of allergic reactions to insect venom allergens, drugs, or chemical allergens
Interpretation
Increased In
- Detection of IgE antibodies in serum (Class 1 or greater) indicates an increased likelihood of allergic disease as opposed to other etiologies and defines the allergens that may be responsible for eliciting signs and symptoms.
Decreased In
Limitations
- The demonstration of sensitization is not sufficient to diagnose an allergy, however, because a sensitized individual may be entirely asymptomatic upon exposure to the allergen in question. Thus, allergy tests must be interpreted in the context of the patients specific clinical history, and the diagnosis of an allergic disorder cannot be based solely on a laboratory result.
- If the result is markedly positive (e.g., a Class VI result), the history suggests a past reaction to the allergen, and the allergen is well characterized, then the diagnosis of an allergy can usually be made without further evaluation. If the result is weakly positive, then further evaluation is usually needed.
- A negative immunoassay result in the setting of a strongly suggestive history does not exclude allergy. In this situation, a skin prick test should be considered (if not contraindicated).
- False-positive results of allergen-specific IgE can theoretically occur in patients with extremely elevated total IgE levels.
- Tests used largely in research settings include immunoblotting, basophil histamine or leukotriene release tests, basophil activation, and levels of eosinophil mediators, etc., are not standardized, and are generally not superior to skin testing, and cannot be recommended for routine clinical use.
- Allergen-specific IgG and IgG4 tests, which are believed to correlate with normal immunologic responses to foreign substances, are not useful in the diagnosis of IgE-mediated allergy, with the exception of venom allergy. Unreliable testing methods include provocation/neutralization tests, kinesiology, cytotoxic tests, and electrodermal testing.
- In food allergy, circulating IgE antibodies may remain undetectable despite a convincing clinical history because these antibodies may be directed toward allergens that are revealed or altered during industrial processing, cooking, or digestion and therefore do not exist in the original food for which the patient is tested.
- Identical results for different allergens may not be associated with clinically equivalent manifestations, due to differences in patient sensitivities.