Autologous Serum Skin Test in Chronic Urticaria

Background: Chronic Urticaria (CU) is a common dermatosis affecting 0.1% population, characterized by recurrent appearance of wheals with or without angioedema for more than 6 weeks. However, in a significant number of these patients, chronic autoimmune urticaria has been identified. Autologous serum skin test (ASST) is a useful diagnostic aid in identifying chronic autoimmune urticaria. Aim: To assess autologous serum skin test in chronic urticaria. Methods: A total of 50 patients with chronic urticaria were taken up for the study and ASST was performed in all the patients. Approximately 0.05 ml (equivalent to 2 units on insulin syringe that has 1 ml marked as 40 units) of autologous serum was injected intradermally over flexor aspect of the left forearm. Equal amount of normal saline (negative control) was injected intradermally over flexor aspect of the right forearm. The results were read after 30 minutes. The test was considered positive if wheal and flare response occurred over the left forearm (serum injection site) with a diameter of at least 1.5 mm or more than that of saline induced response. Results: Out of 50 patients with chronic urticarial, 30 (60%) were autologous serum skin test positive whereas 20 (40%) were autologous serum skin test negative. Conclusion: Positive autologous serum skin test was seen in 60% of patients. It is a simple, practicable in-vivo intradermal clinical test to differentiate chronic idiopathic urticaria from autoimmune urticaria. Key Words: Chronic urticaria, Chronic autoimmune urticaria, Autologous serum skin test, In- vivo intradermal test