Physical urticaria can be confirmed with physical challenge tests. These involve the application of the suspected stimuli (heat, pressure, light, vibration, scratching [dermographism], cold [ice cube]) to the skin. Exercise testing can also be performed to diagnose cholinergic urticaria. Ice cube test findings are typically negative in patients with familial cold autoinflammatory syndrome. With the exception of testing for dermographism, these tests are usually performed only by specialty centers.
Imaging studies generally are not indicated unless a specific finding on clinical examination or history suggests an underlying etiology that may warrant further diagnostic studies.
Selected allergy tests can be performed if food allergy or stinging insect hypersensitivity is suspected. This process may be helpful for some cases of acute urticaria, but these studies are rarely helpful in the evaluation of chronic urticaria. However, they may be needed to rule out an atopic component and label the urticaria as idiopathic. A few research centers perform an autologous serum skin test, but it is currently not a well-established procedure.
A diagnostic skin biopsy is not helpful but should be considered if lesions do not resolve in patients suspected of having urticarial vasculitis (eg, in patients who present with such features as fever, painful lesions, arthralgia, elevated erythroid segmentation rate, lesions that last 24 hours or longer, or lesions that resolve with residual petechiae or purpura).
For more on the workup of urticaria, read here.
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Cite this: William James. Fast Five Quiz: Refresh Your Knowledge on Key Aspects of Acute Urticaria - Medscape - Mar 27, 2018.