A large number of substances have been found to have allergic potential. Measurements of IgE antibodies are useful to establish the presence of allergic diseases and to define the allergen specificity of immediate hypersensitivity reactions. Examples of allergic diseases include asthma, allergic rhinitis, dermatitis, anaphylaxis, and urticaria. In 2010, the National Institute of Allergy and Infectious Diseases established guidelines for testing of IgE levels in suspected food allergy cases.
The fluorescent enzyme immunoassay (FEIA) measures the increase and quantity of allergen-specific IgE antibodies and diagnoses an allergy to a specific allergen (e.g., molds, weeds, foods, insects). These measurements are used in people, especially children, with extrinsic asthma, hay fever, and atopic eczema and are an accurate and convenient alternative to skin testing. Although more expensive, they do not cause hypersensitivity reactions.
Additional antigens are continually being added; up-to-date information should be sought. Examples of categories that can be tested for include grasses, trees, molds, venoms, weeds, animal dander, foods, house dust, mites, antibiotic drugs, and insects.
Based on FEIA, the fluorescence is proportional to the amount of specific IgE present in the patient’s sample.
Fluorescent Enzyme Immunoassay
| Class | IgE kU/L | Interpretation |
|---|---|---|
| 0 | <0.35 | Negative |
| 1 | 0.35–0.69 | Equivocal |
| 2 | 0.70–3.49 | Positive |
| 3 | 3.5–17.4 | Positive |
| 4 | 17.5–49.9 | Strongly positive |
| 5 | 50.0–99.9 | Strongly positive |
| 6 | ≥100 | Strongly positive |
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions.
Label the specimen with the patient’s name, date, and test(s) ordered and place in a biohazard bag for transport to the laboratory.
Positive results greater than or equal to class 2 are strongly associated with allergic symptoms on exposure to allergen.
Clinical Alert
Egg (child): ≥7 IU/mL or ≥7 kIU/L
Milk (child): ≥15 IU/mL or ≥15 kIU/L
Peanuts: ≥14 IU/mL or ≥14 kIU/L
Fish: ≥20 IU/mL or ≥20 kIU/L
Pretest Patient Care
Explain test purpose and procedure.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Negative results effectively rule out allergy induced by that allergen.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.