Evaluation of autologous plasma skin test in patients with chronic idiopathic urticaria.

Summary Background  The pathophysiological mechanism of chronic urticaria is still poorly understood and its aetiology is considered to have an autoreactive basis. Autologous serum skin tests (ASSTs) and autologous plasma skin tests (APSTs) comprise the simplest ways for diagnosing autoreactive urticaria (with autoantibodies, histamine-releasing factor and coagulation factors, especially thrombin) in a clinical setting. However, there are still some questions about the specificity of these tests. Objectives  To evaluate the role of autoreactivity in the pathogenesis of chronic urticaria by means of measuring plasma prothrombin fragments 1 + 2, which are used as markers of thrombin, and to compare the APST with the ASST. Methods  Forty-two patients (19 men and 23 women; mean age 35·7 years, range 28–76) and 35 healthy volunteers (19 men and 16 women; mean age 30·3 years, range 20–80) were included in the study. APST, negative (ASST, sodium citrate, saline) and positive (histamine) control tests were performed in the patient and control groups. The levels of plasma prothrombin fragments 1 + 2 were also assessed. Results  When the APST was evaluated without negative controls, it was positive in 67% of patients. However, the APST was positive in 0% when it was evaluated with negative controls. Levels of prothrombin fragments 1 + 2 were found to be elevated in patients with chronic idiopathic urticaria. Conclusions  We suggest that as negative control tests were not performed along with the APST in previous studies, the APST showed a high rate of positivity. Thus, the use of APST for evaluating autoreactivity in clinical practice is not superior to the use of ASST and further studies should be conducted.