Background. Chronic urticaria is defined as urticaria persisting daily for more than six weeks. A significant number of patients had autoimmune basis where autologous serum skin test is widely used for detection of chronic autoimmune urticaria. Objectives. To estimate the frequency of autoimmune urticarial in Iraqi patients utilizing the autologous serum skin test and to evaluate its results with the variable clinical features of chronic idiopathic urticaria. Methods. In this prospective study, 54 patients with chronic idiopathic urticaria were investigated with autologous serum skin test where its results were examined with the different clinical parameters of chronic autoimmune urticaria. Results. Twenty two patients (40.7%) out of 54 patients with chronic idiopathic urticarial had positive autologous serum skin test. Statistical analysis of the clinical variables did not show a significant difference between patients with positive and negative autologous serum skin test except for the distribution of wheals on the face and extremities which was significantly associated with positive autologous serum skin test results (P value 0.004). Conclusion. Autologous serum skin test is a simple, office-based test for detecting chronic autoimmune urticaria patients who have no distinctive clinical features differentiating them from chronic idiopathic urticaria patients. 1. Introduction Chronic urticaria is defined as urticaria persisting daily or almost daily for more than six weeks [1]. Although in many patients with chronic urticaria the disease remains idiopathic, in the last years, a significant number of patients with chronic urticaria have been proved to have autoimmune causes for their urticaria [2]. The autoimmune subgroup constitutes about 45% of patients previously diagnosed as having chronic idiopathic urticaria (CIU), and it is associated with the IgG anti-IgE receptor alpha subunit in 35–40% of the patients or IgG anti-IgE in additional 5–10%. These autoantibodies have been shown to activate blood basophils and cutaneous mast cells in vitro [3]. The presence of these autoantibodies may be important clinically in a group of severely affected, treatment-resistant patients, where immunomodulatory treatments may be valuable [2]. Clinical examination of the patient with CIU is generally unhelpful in distinguishing autoimmune from nonautoimmune patients [4]. Autologous serum skin test (ASST) is a simple in vivo clinical test for the detection of basophil histamine-releasing activity. Sabroe et al. found that ASST has a sensitivity of approximately 70% and
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