Evaluation of the PFA-100 system for monitoring desmopressin therapy in patients with type 1 von Willebrand's disease.

The platelet function analyzer PFA-100 (Dade International Inc., FL, USA) is a relatively novel method for rapid in vitro global evaluation of primary hemostasis.1 Since the PFA-100 has been shown to be very sensitive to platelet and von Willebrand factor (VWF) levels and function, it is useful mainly as a screening test for von Willebrand’s disease (VWD) and several platelet disorders.2,3 Recently, the PFA-100 has been proposed for therapeutic monitoring of patients with VWD treated with desmopressin (DDAVP) or factor VIII/VWF concentrate.4,5 In the present study, we evaluated the PFA-100 system in 24 patients with type 1 VWD, before and 1 hour after the subcutaneous injection of DDAVP at a dose of 0.3 μg/Kg. The median age of the 24 patients was 34.2 years (range 21 to 43 years) and the male/female ratio was 1.2. Closure time (CT) on the PFA-100 system was measured with both collagen/ADP (CT-ADP) and collagen/epinephrine (CT-Epi) cartridges. We also tested the effects of the DDAVP test on plasma concentrations of VWF antigen (VWF:Ag), VWF activity (VWF:ristocetin cofactor, RCo), coagulation factor VIII (F VIII:C) and bleeding time (BT) according to Ivy. The results are shown in Table 1. All patients had prolonged APTT and CT with both cartridges and decreased VWF:Ag and VWF:RCo levels at baseline. The baseline factor VIII levels were decreased and the bleeding time was prolonged in 10 (41.7%) and 19 (79.2%) patients, respectively. Subcutaneous DDAVP injection induced normalization of VWF:Ag and VWF:RCo in all patients with a mean increase over the baseline of 2.8 (range 1.4-3.8) and 2.9 (range 1.6-4.2) times, respectively. The mean factor VIII increase over the baseline was 2.5 (range 1.2-3.6) times. Desmopressin also shortened BT and CT with both types of cartridges in all patients. As observed in previous reports,4,5 normalization of PFA-100 results postDDAVP correlated well with the increase in VWF. In our study, the diagnostic sensitivity of the PFA-100 system for patients with type 1 VWD was greater than that of the BT. In fact, all 24 patients (100%) with type 1 VWD had abnormal basal CT as measured with both collagen/ADP and collagen/epinephrine cartridges, whereas a prolonged BT was recorded in 19 patients (79.2%, p <0.001). Therefore, our results substantially agree with earlier ones4,5 and confirm that the PFA-100 system might be a useful tool for diagnosis and therapeutic monitoring of patients with VWD. Moreover, since the PFA-100 system appears to be more sensitive and less invasive, we believe that it could represent a valid and reliable alternative to BT as a screening test for type 1 von Willebrand’s disease.6