[Assessment of the usefulness of autologous serum skin testing in chronic urticaria: a retrospective single-centre study of 74 patients]

Background: Chronic urticaria (CU) is a debilitating disease, and patients and their physicians often seek an aetiological explanation. Studies have suggested that idiopathic CU is associated with the presence of serum auto-antibodies that may be detected by autologous serum skin test (ASST).

Aim: To confirm the frequency of positivity of ASST and to evaluate its usefulness and possible correlation with the severity of urticaria (greater resistance to AH1, greater activity score or longer duration).

Patients and methods: Patients referred for CU between 1 October 2001 and 31 March 2005 were submitted to standardized explorations including clinical examination, physical tests, CBC, ESR, CRP and anti-thyroperoxidase antibodies, and an ASST was ordered. Inclusion criteria included no discernible cause of CU, acceptance of the protocol, including blood sampling and injection of ASST 3 weeks later, serological tests for HBV, HCV and HIV, and discontinuation of anti-H1 agents and corticosteroids. Exclusion criteria comprised the presence of dermographism, physical urticaria, urticarial vasculitis, and failure to discontinue anti-H1 drugs or corticosteroids. In April 2006, we contacted patients by mail to assess their current treatment, their CU activity score or its resolution.

Results: Seventy-four patients (67 women, seven men) of mean age 43 years were included. ASST was positive in 43 patients (58 %) and negative in 31 (42 %). The only noticeable difference, although not statistically significant (p=0.23), was a positive anti-thyroperoxidase antibody result in 12 % of patients with negative ASST versus 24 % of patients with positive ASST. The occurrence of angioedema, the duration of CU, the severity score, the relative inefficiency of AH1 and the use of corticosteroids or cyclosporine were similar between the two groups.

Discussion: ASST was positive in more than half of the patients with idiopathic CU both in our study and in the literature, with sensitivity of around 70 % and specificity approaching 80 %. However, while this test can help patients understand their disease better and avoid both a fruitless search for other causes and unnecessary proscription of food allergens, our study shows that positive or negative ASST results have no bearing on treatment and are not associated with greater severity of urticaria or greater resistance to treatment. Consequently, we do not recommend routine use of ASST in patients presenting idiopathic CU.