Among 350 patients, 17% of test results were outside the normal range, but only 1.6% led to further evaluation, and only one patient benefited.
Even with extensive testing, a cause for chronic urticaria (CU) rarely is established. Although not evidence based, U.S. practice parameters from 2000 recommend complete blood count (CBC), urinalysis, liver function tests, erythrocyte sedimentation rate (ESR), and thyroid-stimulating hormone (TSH) measurement (Ann Allergy Asthma Immunol 2000; 85:521). European guidelines recommend only CBC and ESR (Br J Dermatol 2001; 144:708). Cleveland Clinic researchers conducted a retrospective review of 356 patients (69% women) with CU at their allergy clinic.
Patients underwent a median of six tests (total, 1872), and 17% of studies were abnormal. The most commonly ordered tests were TSH (performed in 74% of patients), CBC (73%), comprehensive or basic metabolic panels (71%), ESR (60%), antithyroid antibodies (50%), urinalysis (39%), and antinuclear antibodies (37%); 1.6% of abnormal tests results led to further work-ups, including specialist consultation or additional laboratory testing. Only one patient seemed to benefit from such testing: Her thyroxine dose was increased based on a high TSH result, and her urticaria resolved.
Comment: A careful history and physical examination typically can identify any modifiable or dangerous causes of urticaria, such as vasculitis, physical triggers (i.e., dermatographism), or allergens. For patients with only angioedema, C1 inhibitor deficiency must be considered. For patients with typical CU, routine laboratory testing probably doesn’t aid in diagnosis or management.
— David J. Amrol, MD
Dr. Amrol is an Associate Professor of Clinical Internal Medicine and Director of the Division of Allergy and Immunology at the University of South Carolina School of Medicine in Columbia.
Published in Journal Watch General Medicine September 29, 2011