Indicated Supporting Diagnostic Data

Case history is critical to the discovery of a specific cause in acute, intermittent, or chronic urticaria. Testing should be guided by historical data, and extensive blind testing is seldom productive. History should be repeated periodically, as the victim may recall forgotten information or, over time, may make new associations.

Biopsy

Biopsy is seldom indicated for urticaria; when a question arises regarding common hives versus urticarial vasculitis (see Differential Diagnosis section), biopsy will help to distinguish them.

Avoidance Testing

This should be done in a staged fashion, eliminating first any suspect allergens and any substances known to cause pseudoallergic hives or nonspecific histamine or mediator release. With severe symptoms or with chronic disease, an avoidance diet with staged reintroduction of different food groups may be useful.

If there is a significant eosinophilia, this suggests either a type I hypersensitivity reaction or possibly intestinal parasites.

Stool Exam for Ova and Parasites

This is indicated if travel history, GI history, or CBC suggests this possibility.

Radiologic Studies

In chronic urticaria, sinus films and apical dental films have the highest yield. They may be positive even when symptoms are absent. Other X-rays should be ordered strictly by indications from a general history and physical exam.

Skin Testing

This form of testing requires special skills and may on occasion provoke a life-threatening reaction. Interpretation and a familiarity with the proper concentrations and quality of the antigens is essential. In the authors' opinion, these studies should be carried out only by a qualified allergist or a practitioner with equivalent training.

Serum IgE Determination

Although this test may support suspicion for an allergic cause, it is a very nonspecific test especially in the presence of atopic disease. It is rarely indicated.

Radioallergosorbent (RAST) Testing

These tests are expensive, controversial, difficult to interpret, and subject to false-negative results. Their use should be authorized by a qualified allergist.

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