Chronic Urticaria Workup

Updated: Jul 31, 2018
  • Author: Marla N Diakow, MD; Chief Editor: William D James, MD  more...
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Workup

Laboratory Studies

The information elicited from the history and physical examination is used to direct the selection of laboratory tests. While in most cases no diagnostic testing may be necessary, targeted laboratory testing based on clinical suspicion is appropriate. In most patients, the only screening tests that are recommended to be performed are a complete blood cell (CBC) count with differential, erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP), liver enzymes, and thyrotropin (TSH). [9]

A CBC count with differential should be done. In patients with parasitic infections, especially in developing countries, or patients experiencing a drug reaction, the eosinophil count may be elevated.

Examination of the stool for ova and parasites should be considered in patients with gastrointestinal (GI) tract symptoms, an elevated eosinophil count, or a positive travel history. The absence of blood eosinophilia may render stool examination for ova unnecessary.

The ESR may be elevated in persons with urticarial vasculitis. Antinuclear antibody (ANA) titers are indicated when urticarial vasculitis is suspected. ESR, CRP, ANA, and rheumatoid factor (RF) testing should be performed if additional features of an underlying rheumatologic disorder are found.

Hepatitis B and C titers may be helpful. Both hepatitis B and C may be associated with cryoglobulinemia, which is associated with some forms of cold-induced urticaria and urticarial vasculitis. In addition, an association has been reported between hepatitis C and chronic urticaria. [31]

Serum cryoglobulin and complement assays may be useful. Cryoglobulinemia is associated with some forms of cold-induced urticaria. C3 (associated with pulmonary involvement in a subset of patients with urticarial vasculitis), C4 (sometimes low in hereditary angioedema), and C1-esterase inhibitor (associated with hereditary angioedema) functional assays may be performed.

Thyroid function testing and antithyroid microsomal and peroxidase antibody titers may also be useful. Patients with urticaria unresponsive to antihistamines or steroids may have elevated titers, which may respond to thyroid hormone therapy. [1] Patients may be euthyroid. Urticaria is also more common in patients with Hashimoto thyroiditis. The presence of antithyroglobulin and antimicrosomal antibodies supports the diagnosis of chronic immunologic urticaria. The plasma thyrotropin level helps screen for thyroid dysfunction.

The Chronic Urticaria (CU) Index is not widely available and is only performed at a few reference laboratories. Patients with a chronic form of urticaria who have a positive functional test result for autoantibody to the Fc receptor of IgE—that is, anti-FcεR—likely have an autoimmune basis for their disease. A positive result does not indicate which autoantibody (anti-IgE, anti-FcεRI, or anti-FcεRII) is present. This test is usually combined with thyroid function testing, antithyroid microsomal titers, and peroxidase antibody titers.

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Other Tests

Other tests that may be required include challenge testing. Testing to cold, pressure, heat, ultraviolet light, and visible light may be required to exclude a physical urticaria. [32]

Prick or radioallergosorbent assay testing may be useful if contact urticaria is suggested. Skin prick test results may help identify a food allergy, which is a rare cause of chronic urticaria.

Although histologic examination is not necessary for the diagnosis of urticaria, a skin biopsy is necessary for the diagnosis of urticarial vasculitis or a neutrophil-predominant pattern of urticaria that may not respond well to antihistamines. A skin biopsy is indicated for patients in whom individual urticarial lesions persist for more than 24 hours or are associated with petechiae or purpura and for patients with systemic symptoms such as fever, arthralgia, or arthritis.

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Histologic Findings

Characteristic histologic findings include dermal edema, blood vessel dilatation, and a mild perivascular infiltrate predominantly consisting of monocytes and CD4+ lymphocytes; some forms exist in which neutrophils predominate.

Histologic evidence of leukocytoclasia (neutrophilic infiltration with fragmentation of nuclei) is a characteristic feature of urticarial vasculitis. The presence of neutrophils may indicate potential benefit from treatment with dapsone or colchicine.

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