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Chronic urticaria has been uncommonly associated with systemic diseases such as collagen vascular disease or malignancy. In a meta-analysis by Kozel and colleagues, an underlying disease was considered to be the cause of chronic urticaria in only % of patients. 5 For patients with chronic urticaria, screening laboratory tests may be completed to help detect underlying illness. These tests can include a complete blood count with differential, erythrocyte sedimentation rate, urinalysis, and liver function tests. 29 Because thyroid autoimmunity has been associated with chronic urticaria, thyroid function tests including antimicrosomal and antithyroglobulin antibodies may be obtained. 35 If a connective tissue disease is suspected, antinuclear antibody and other serologic tests may be warranted. 35 A C4 level should be obtained in patients who experience angioedema without urticaria. If the C4 level is low, then C1 inhibitor level and function should be checked to evaluate further for possible hereditary or acquired angioedema.