IgE antibodies are responsible for hypersensitivity reactions described as atopic (allergic) or anaphylactic. Examples of IgE-mediated diseases include hay fever, asthma, certain types of eczema, and idiosyncratic, potentially fatal reactions to insect venoms, penicillin, and other drugs or chemicals.

Almost all of the body's active IgE is bound to tissue cells, with only small amounts in the blood. Thus, IgE antibodies cannot circulate in search of antigen but must wait for antigens to appear in their area. Once this happens, the interaction of IgE antibodies with specific antigens causes mast cells (tissue basophils) to release histamine and other substances that promote vascular permeability.²⁶

The radioallergosorbent test (RAST) for IgE measures the quantity of IgE antibodies in the serum after exposure to specific antigens selected on the basis of the person's history. RAST has replaced skin tests and provocation procedures, which were inconvenient, painful, and hazardous to the client.

• If the client is not allergic to the antigen, IgE antibody is not detected. A positive test result in relation to a specific antigen is more than 400 percent of control. Results of the test may vary depending on the reference serum used for the control.

• Radioisotope tests within 1 week before the test may alter results.

• Onset of asthma, hay fever, dermatitis
• Systemic reaction to insect venom, drugs, or chemicals
• Identification of the specific antigen(s) to which the client reacts
• Monitoring of response to desensitization procedures

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• All clients should be interviewed to determine whether they have undergone any radioisotope tests within the past week.

A venipuncture is performed and the sample collected in a red-topped tube or other type of blood collection tube, depending on laboratory preference. The allergy panel desired should be indicated on the laboratory request form. Each panel usually consists of six antigens.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Complications and precautions: Instruct client to avoid contact with substances, ingestion of drugs, or exposure to insects that cause reactions.