Background: Chronic autoimmune urticaria (CAU), a subgroup of chronic idiopathic urticaria (CIU), is characterized by severe and persistent wheals accompanied by redness and itching. Diagnosis is almost completely based on clinical suspicion and the results of the autologous serum skin test (ASST).

Objectives: To determine the frequency of CAU and compare the clinical and laboratory parameters of patients with positive and negative ASST results.

Patients and Methods: A total of 165 patients with chronic urticaria (CU) were enrolled; 31 were excluded (known causes and pregnancy/breastfeeding), leaving 134 patients with CIU. A clinical evaluation and routine and specific laboratory tests were performed.

Results: The cause of CU was identifi ed in 18.9% of patients; 81.2% patients were considered to have CIU. The ASST result was positive in 39.6% of patients with CIU, who had more frequent urticaria attacks than patients with a negative ASST result. Patients with positive results had a higher urticaria activity score than those with negative results, although the difference was not statistically significant. As for immunological markers, the absolute eosinophil count and serum immunoglobulin (Ig) E titer were lower in patients with a positive ASST result than in those with a negative ASST result, although, again, the difference was not statistically signifi cant (P=.07). Antithyroid antibody titer and B-cell percentage were higher in patients with a positive ASST result than in those with a negative result, and the difference was statistically significant (P=.04 and .004, respectively).

Conclusions: ASST remains a baseline diagnostic test for CAU. Patients with CAU had more frequent attacks and higher antithyroid antibody titers and peripheral B-cell percentages, as well as lower absolute eosinophil counts and serum IgE concentrations.

Key words: Autologous serum skin test. Chronic urticaria. Autoimmunity.