Allergen-Specific Immunoglobulin E

Synonym/acronym: Allergen profile, radioallergosorbent test (RAST), ImmunoCAP^® Specific IgE.

Common use

To assist in identifying environmental allergens responsible for causing allergic reactions.

Specimen

Serum (2 mL per group of six allergens, 0.5 mL for each additional individual allergen) collected in a gold-, red-, or red/gray-top tube.

Normal findings

(Method: Radioimmunoassay or fluorescence enzyme immunoassay)

RAST Scoring Method (Radioimmunoassay) and ImmunoCAP^® Scoring Guide (Fluorescence Enzyme Immunoassay)	Conventional and SI units Allergen Specific IgE
Specific IgE Allergen Antibody Level	kU/L
Absent or undetectable allergy	Less than 0.35
Low allergy	0.35–0.7
Moderate allergy	0.71–3.5
High allergy	3.51–17.5
Very high allergy	17.5–50
Very high allergy	51–100
Very high allergy	Greater than 100

Description

Allergen-specific immunoglobulin E (IgE) is generally requested for groups of allergens commonly known to incite an allergic response in the affected individual. The test is based on the use of a radiolabeled or non-radiolabeled anti-IgE reagent to detect IgE in the patient’s serum, produced in response to specific allergens. The panels include allergens such as animal dander, antibiotics, dust, foods, grasses, insects, trees, mites, molds, venom, and weeds. Allergen testing is useful for evaluating the cause of hay fever, extrinsic asthma, atopic eczema, respiratory allergies, and potentially fatal reactions to insect venom, penicillin, and other drugs or chemicals. RAST and non-radiolabeled methods are alternatives to skin test anergy and provocation procedures, which can be inconvenient, painful, and potentially hazardous to patients. ImmunoCAP^® FEIA is a newer, nonradioactive technology with minimal interference from nonspecific binding to total IgE versus allergen-specific IgE.

A nasal smear can be examined for the presence of eosinophils to screen for allergic conditions. Either a single smear or smears of nasal secretions from each side of the nose should be submitted, at room temperature, for Hansel staining and evaluation. Normal findings vary by laboratory but generally, greater than 10–15% is considered eosinophilia or increased presence of eosonophils. Results may be invalid for patients already taking local or systemic corticosteroids.

This procedure is contraindicated for

N/A

Indications

Evaluate patients who refuse to submit to skin testing or who have generalized dermatitis or other dermatopathic conditions
Monitor response to desensitization procedures
Test for allergens when skin testing is inappropriate, such as in infants
Test for allergens when there is a known history of allergic reaction to skin testing
Test for specific allergic sensitivity before initiating immunotherapy or desensitization shots
Test for specific allergic sensitivity when skin testing is unreliable (patients taking long-acting antihistamines may have false-negative skin test)

Potential diagnosis

Different scoring systems are used in the interpretation of RAST results.

Increased in

Related to production of IgE, the antibody that primarily responds to conditions that stimulate an allergic response
Allergic rhinitis
Anaphylaxis
Asthma (exogenous)
Atopic dermatitis
Echinococcus infection
Eczema
Hay fever
Hookworm infection
Latex allergy
Schistosomiasis
Visceral larva migrans

Decreased in

Asthma (endogenous) Pregnancy Radiation therapy

Critical findings

N/A

Interfering factors

Recent radioactive scans or radiation within 1 wk of the test can interfere with test results when radioimmunoassay is the test method.

Nursing Implications and Procedure

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this test can assist in identification of causal factors related to allergic reaction.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
Obtain a history of the patient’s immune and respiratory systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Note any recent procedures that can interfere with test results.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

Potential complications: N/A
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Inform the laboratory of the specific allergen group to be tested. Perform a venipuncture.
Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding and hematoma formation and secure gauze with adhesive bandage.
Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
Nutritional Considerations: Should be given to diet if food allergies are present. Lifestyle adjustments may be necessary depending on the specific allergens identified.
Recognize anxiety related to test results. Administer allergy treatment if ordered. As appropriate, educate the patient in the proper technique for administering his or her own treatments as well as safe handling and maintenance of treatment materials. Treatments may include eye drops, inhalers, nasal sprays, oral medications, or shots. Remind the patient of the importance of avoiding triggers and of being in compliance with the recommended therapy, even if signs and symptoms disappear.
Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include arterial/alveolar oxygen ratio, blood gases, CBC, eosinophil count, fecal analysis, hypersensitivity pneumonitis, IgE, and PFT.
See the Immune and Respiratory systems tables at the end of the book for related tests by body system.