Allergen Specific IgE
By William H. Wong, Ph.D., December 3, 1996
The diagnosis of human allergic disease involves the combined use of a careful clinical history, physical examination, and in vivo and in vitro assay methods for the detection of IgE antibodies of defined allergen specifications.
IgE immunoglobulins have been demonstrated to be mediators in diseases of immediate type hypersensitivity – including allergic asthma, rhinitis, urticaria, and atopic dermatitis. All these conditions are the result of the interactions of an allergen, the specific IgE, and the mast cells and basophils. When an allergen binds to the IgE antibodies attached to a mast cell or basophil, changes in the cellular membrane occur. The mast cells or basophils release their granules with or without the cells rupturing. Additional substances, such as histamine, substance A, eosinophil chemotactic substance, and platelet activating factors are also secreted. The body’s responses to these substances include dilation of local blood vessels, attraction of eosinophils and neutrophils to the reaction site, increasing permeability of the capillaries and loss of fluid into the tissues.
Historically, Radioallergosorbent test (RAST) was the first immunoassay system available for the measurement of human IgE antibodies to specific defined allergens in serum. In its original form, RAST employed a paper disc to which allergen is covalently attached (allergosorbent) and to bind allergen-specific antibodies of all isotypes. Bound IgE was detected using I125-labeled polyclonal anti-human IgE. Results are reported in classes and in arbitrary units from a reference curve. Many improvements and modifications of this have been commercialized since then, including PRIST and Pharmacia’s CAP system. The current commercially available reagents for total IgE and allergen-specific IgE antibodies are significantly better in terms of analytical sensitivity and specificity, and reproducibility.
The concentration of IgE in the serum is highly age dependent. IgE concentrations are low in cord serum, usually less than 5 IU/mL. The serum IgE levels progressively increase in healthy children up to age of 10 to 15 years. Atopic infants have an earlier and steeper increase in IgE levels compared with non-atopic children. Serum IgE levels that are significantly higher than the age-adjusted, non-atopic reference ranges are considered abnormally elevated and are highly suggestive of atopic disorders, such as allergic rhinitis, asthma, and atopic dermatitis. Extreme elevations in serum IgE are observed commonly in parasitic infections and hyperglobulinemia E syndrome. However, while elevated total serum IgE are useful in confirming the clinical diagnosis of allergic diseases, a normal or low value does not rule out the possibility of IgE-mediated conditions. Total serum IgE levels must be interpreted carefully within the relevant clinical context.
The presence of allergen-specific IgE antibody in the serum of a patient is highly predictive of the likelihood that the individual will exhibit immediate hypersensitivity upon exposure to the allergen. The determination of allergen-specific IgE antibodies, combined with total serum IgE, is a very sensitive first-order test for allergic disease. And, unlike the measurement of total serum IgE, a negative result effectively rules out allergy induced by the allergen tested.
Numerous technical reports have appeared in the literature comparing skin testing with in vitro allergen specific IgE, mostly to assess which method is better in terms of clinical sensitivity and specificity. In general, the performance of each method appears to be allergen dependent, with the in vitro serum testing better for some allergens (such as food allergens) and the skin testing better for some other allergens. However, unlike skin tests, in vitro allergen specific IgE test results are not affected by antihistamine, beta blockers and other cardiac medications, and can be used even for patients with widespread dermatopathic conditions.
Allergen specific IgE testing is indicated for:
- Identifying specific allergen sensitivity before the initiation of desensitizing immunotherapy,
- Evaluating pediatric patients with atopic disease,
- Determining food allergy,
- Evaluating patients with severe allergic reactions to skin testing , and
- Testing patients on specific medications that will interfere with skin testing.
Methodology and Reference Values
At Diagnostic Laboratory Services, total serum IgE is measured using an enzyme immunoassay (BMC). Results are reported in IU/mL (for conversion to ng, 1 IU = 2.44 ng). The following are the reference ranges for total IgE:
|Newborn – 1 year||<5 IU/mL|
|2 – 4 years||<12 IU/mL|
|5 – 7 years||<40 IU/mL|
|8 – 15 years||<80 IU/mL|
|15 years||<100 IU/mL|
Allergen-specific IgE assays are performed using Pharmacia’s CAP system, which is substantially more sensitive and reproducible than the previous Pharmacia Phadebas RAST system. The results are reported as %Ref (fluorescence unit as a percent of the IgE standard of 0.35 KU/L) as well as the CAP RAST ASM class:
|%Ref||CAP RAST ASM class||Level of allergen specific IgE|
|60 – 70||0 to 1||Equivocal|
|70 – 110||1||Detection limit|
|220-600||3||Increasing levels of|
|600 – 3000||4||allergen specific IgE|
|2000 – 6000||5||--|
A definitive clinical diagnosis should not be based solely on the allergen-specific IgE result, but should only be made after all clinical and laboratory findings are evaluated.
American Academy of Allergy and Immunology. “The use of in vitro tests of IgE antibody in the specific diagnosis of IgE-mediated disorders and in the formulation of allergen immunotherapy”, J Allerg Clin Immunol 90: 263-267 (1992).
Barbee RA, Halomen M, Lebowitz M, Burrows B. “Distribution of IgE in a community population sample: Correlations with age, sex, and allergen skin test reactivity”, J Allerg Clin Immunol 68: 106-111 (1981).
Del Monte A, Zaccherini P, Tomasini C. “Comparison between Pharmacia CAP System and skin prick test in allergic diseases”, Proceedings of Congress of the European Academy of Allergology and Clinical Immunology, Zurich, Switzerland. May 26-29, 1991.
Eriksson NE. “Allergy screening with Phadiatop and CAP Phadiatop in combination with a questionnaire in adults with asthma and rhinitis”, Allergy 45: 285-292 (1990).
Gueant JL, Moneret-Vautrin DA, Dejardin G, et al. “Comparative evaluation of RAST and FAST for 11 allergens in 288 patients”, Allergy 44: 204-208 (1989).
Kelso JM, Sodhi N, Gosselin VA. “Diagnostic performance characteristics of the standard Phadebas RAST, modified RAST, and Pharmacia CAP system versus skin testing”, Ann Allergy 67: 511 (1991).
King TP, Hoffman D, Lowenstein H, et al. “Allergen nomenclature”, J Allerg Clin Immunol 96: 5-14 (1995).
NCCLS. Proposed Guidelines: Evaluation Methods and Analytical Performance Characteristics of Immunological Assays for Human Immunoglobulin E (IgE) Antibodies of Defined Allergen Specificities. NCCLS, Wayne, PA. 1996.
Ortolani C, Ispano M, Pastorello EA, et al. “Comparison of results of skin prick tests (with fresh foods and commercial food extracts) and RAST in 100 patients with oral allergy syndrome”, J Allerg Clin Immunol 83: 683-900 (1989).
Ownby DR, Anderson JA, Jacob GL, Homburger HA. “Development and comparative evaluation of a multi-allergen RAST as a screening test for inhalant allergy”, J Allerg Clin Immunol 73:466-472 (1984).
Ownby DR. “Allergy testing: In vitro versus In vivo”, Pediatr Clin North Am 35:995-1009 (1988).
Shearer WT. “Specific diagnostic modalities: IgE, Skin tests and RAST”, J Allerg Clin Immunol 84: 1112-1116 (1989).
Williams PB, Dolen WK, Koepke JW. “Comparison of skin testing and three in vitro assays for specific IgE in the clinical evaluation of immediate hypersensitivity”, Ann Allergy 68:35 (1992).
Williams PB, Dolen WK, Koepke JW, Selner JC. “Immunoassay of specific IgE: use of a single point calibration curve in the modified radioallergosorbent test”, Ann Allergy 69: 48-52 (1993).
Wittig HJ, Belloit J, DeFilippi I, Royal G. “Age-related serum IgE levels in healthy subjects and in patients with allergic disease”, J Allerg Clin Immunol 66: 305-313 (1980).
|Test Code||Test Name||List Price|
|4200 – 4224||Allergen Specific IgE (specify the number of allergens, 1 to 25)||$16.00 for each allergen|
Allergens available at DLS
Test Performing Sites:
- DLS Central Laboratory – Special Chemistry.
- Allergens not listed on the next page will be sent to a reference laboratory.
- Total IgE: Serum (SST or Red top tube), 1.0 (min. 0.5) mL
- Allergen specific IgE: Serum (SST or Red top tube)
|1 to 3 allergens||1.0 (min. 0.5) mL||4 to 8 allergens||1.5 (min. 1.0) mL||9 to 14 allergens||2.0 (min. 1.4) mL||15 to 20 allergens||2.5 (min. 2.0) mL||21 to 25 allergens||3.0 (min. 2.4) mL|
Store specimens refrigerated below 4C. Stable for at least 30 days at 4C.
- Total IgE: 2 days
- Allergen specific IgE (at DLS): 3 days
- Allergen specific IgE (at reference laboratories): as specified by the reference laboratory.
d1 D. pteronyssinus
d2 D. farinae
h1 Greer house dust
e1 Cat dander/epithelium
e4 Cow dander
e5 Dog dander/epithelium
e70 Goose feather
e85 Chicken feather
e86 Duck feather
m1 Penicillum notatum
m2 Cladosporium herbarum
m3 Aspergillus fumigatus
m4 Mucor racemosus
m5 Candida albicans
m6 Alternaria tenius
m8 Helminthosporium halodes
m10 Stemphylium botyosum
m12 Aureobasdium pullulans
m13 Phoma betae
g2 Bermuda grass
g4 Fescue Meadow
g9 Red Top
g10 Johnson grass
g17 Bahia grass
f256 Black walnut/English walnut
f245 Egg mix
Rf287 Kidney bean
Rf315 Green bean
f1 Egg white
Perennial Panel: includes
d1, d2, e1, e4, e5, e70, e85, e86, m1, m2, m3, m4, m5, m6, m8, m10, m12, m13
k83 Cotton seed
w18 Yellow Dock/Sheep sorrel weed