The autologous serum skin test: a screening test for autoantibodies in chronic idiopathic urticaria

One-third of patients with chronic idiopathic urticaria (CIU) have circulat ing functional autoantibodies against the high affinity IgE receptor Fc eps ilon RI, or IgE. The intradermal. injection of autologous serum causes a we al and flare reaction in many patients with CIU, and this reaction forms th e basis of the autologous serum skin test (ASST). We have determined the pa rameters of the ASST which define the optimal sensitivity and specificity f or the identification of patients with autoantibodies. Two physicians (R.A. S. and C.E.H.G.) performed ASSTs in a total of 155 patients with CIU, 40 he althy control subjects, 15 patients with dermographism, nine with cholinerg ic urticaria and 10 with atopic eczema. Patients were classified as having functional autoantibodies by demonstrating in vitro serum-evoked histamine release from the basophils of two healthy donors. There were significant di fferences (P < 0.001) in the mean weal diameter, weal volume, weal. redness and flare area of the intradermal serum-induced cutaneous responses at 30 min between patients with CIU with autoantibodies and either those without autoantibodies or control subjects. The optimum combined sensitivity and sp ecificity of the ASST was obtained ifa positive test was defined as a red s erum-induced weal: with a diameter of greater than or equal to 1.5 mm than the saline-induced response at 30 min. For R.A.S. and C.E.H.G., the ASST se nsitivity was 65% and 71% and specificity was 81% and 78%, respectively. Us ing these criteria, the following subjects had positive ASSTs: none of 15 d ermographics, none of 10 atopics, one of nine cholinergics and one of 40 co ntrols.