A 13-year-old female presented with a 4-month history of worsening urticaria frequently associated with angioedema and hardly controlled by high doses of antihistamine (10 mg daily). Urticaria did not seem to be triggered by physical stimuli.

Specific IgE against common foods and aeroallergens were negative; full blood count, C3 and C4 complement fractions, ESR and thyroid function were normal. Main autoantibodies were absent. Since every attempt to slow down the antihistamine dosage had led to immediate and severe urticaria/angioedema relapse, we decided to perform an intradermal injection of the patient's serum also in her own mother. After 15 min, a little weal appeared on the patient's forearm, and a large weal appeared on her mother (Fig. 1). We diagnosed chronic autoimmune urticaria (CAU).

Fig. 1
figure 1

Autologous serum skin test: a little weal (diameter, 10 mm) appeared on the patient's forearm, and a large weal (diameter, 18 mm) appeared on her mother's forearm 15 min after intradermal injection of the patient's own serum

Full size image

Overall, 0.1–3 % of children are diagnosed with chronic urticaria (CU) [2]. In nearly 30 % of patients with CU, active autoantibodies against IgE or its receptor have been identified [2, 3]. The autologous serum skin test is an in vivo clinical test which has been suggested as a screening tool for CAU [2, 3]. Interestingly, despite full antihistamine therapy, the patient test resulted positive, although much less pronounced. This incomplete test inhibition by antihistamine therapy has already been reported in the literature [1].