Rationale for the autologous serum skin test in acute versus chronic urticaria

Introduction
Autologous serum skin test (ASST) is a rapid, in-vivo clinical test to detect functional autoantibodies in patients with chronic spontaneous urticaria (CSU), but the rationale for its use in acute urticaria (AU) is unknown.

Aim
To evaluate the efficacy of ASST among patients with AU or CSU.

Material and methods
Treatment-naïve adult (age ≥ 18 years) patients with a diagnosis of AU (< 6 weeks’ duration) and CSU were enrolled prospectively in a cross-sectional study. Healthy age- and sex-matched subjects served as controls. Besides a detailed history and physical examination, ASST, total immunoglobulin E (IgE), freeT3 (fT3), freeT4 (fT4), anti-thyroglobulin, and anti-TPO levels were assessed in all subjects.

Results
Of 101 subjects, mean age was 34.35 ±12.68 years and the study comprised 58.4% of females with no difference between AU (n = 27), CSU (n = 46), and control groups (n = 28). The ratio of positivity in ASST was similar between AU (25.9%) and CSU groups (21.7%), but higher than in controls (10.7%, p = 0.33 for all). The ratio of patients with high total IgE levels (> 100 IU/ml) in AU (85.2%) and CSU (65.2%) groups was similar (p = 0.06), but significantly higher than in the control group (10.7%) (p < 0.001 and p < 0.001). The CSU group had significantly higher abnormal thyroid test results (45.7%) than AU (14.8%) and control groups (3.6%) (p = 0.01 and p < 0.001), whereas patients with clinically diagnosed thyroiditis were only in the CSU group (6.5%). In logistic regression analysis, there was no relation found among the possible risk factors for ASST, even if analysed separately as AU, CSU and control groups.

Conclusions
Even though thyroid function test levels were found to be related with CSU, and total IgE was associated with urticaria, ASST was found to be of importance. This study confirms that ASST was insufficient to demonstrate autoimmunity and acute-chronic urticaria nature. Further tests indicating auto-antibodies in AU and CSU are needed.