Background  Autologous serum skin test (ASST) is an in vivo test to demonstrate circulating endogenous proinflammatory or wheal-inducing factors in urticaria patients. While ASST was negative in a patient with solar urticaria and in a patient with localized heat urticaria, test results turned to positive when performed with visible light-irradiated and heated serums, respectively. These data suggest that some factors and/or antibodies in serum may be activated or inhibited with different factors. We aimed to investigate whether or not ASST results change when performed with narrowband ultraviolet B (UVB)-irradiated serum.

Materials and methods  Seventy-seven patients with chronic idiopathic urticaria underwent ASST twice in consecutive days. The second ASST was performed with narrowband UVB-irradiated serum. The results of the first and second ASSTs were compared.

Results  The first ASST results were positive in 46 (59.7%) patients. ASST results reversed oppositely in 36 (46.8%) patients, turned from negative to positive in 19 patients, and turned from positive to negative in 17 patients when performed with narrowband UVB-irradiated serum.

Conclusion  Our results suggest that narrowband UVB may have modifying effects on some wheal-inducing factors and/or antibodies. On which factors in serum narrowband UVB has effects may be investigated.