Letter: Relation of von Willebrand factor to bleeding time

Efficacy of fresh-frozen plasma and cryoprecipitate in dogs with von Willebrand's disease or hemophilia A

Here we report the comparative efficacy of fresh-frozen plasma (FFP) and cryoprecipitate in the treatment of 2 inherited bleeding disorders in dogs. The dogs were divided into 3 groups, consisting of 4 Doberman Pinschers with type I von Willebrand's disease (vWD) (group 1), 1 Scottish Terrier with type III vWD (group 2), and 4 German Shepherd Dogs with hemophilia A (group 3). In vWD, therapeutic efficacy was determined by the ability of the products to increase von Willebrand factor antigen (vWf:Ag) concentrations above 35 canine units (CU)/dL and to correct the prolonged buccal mucosal bleeding time. Therapeutic efficacy in hemophilia A was assessed by the ability of the products to increase the factor VIII coagulant (FVIII:C) activity above 30 CU/dL. In both groups 1 and 2, higher increases in vWf:Ag were achieved with cryoprecipitate than with FFP, despite a significantly smaller total amount of vWf:Ag (in CU) being infused with cryoprecipitate. The maximum vWf:Ag attained after infusion in group 1 was dependent on both the baseline vWf:Ag concentration and on the type of infusion product. The dogs with vWD in both groups also displayed a delayed increase in FVIII:C activity after infusion of both plasma products, which is characteristic of the disease. In group 3, cryoprecipitate achieved similar increases in FVIII:C activity compared to FFP, although a significantly lesser amount of FVIII:C (in CU) was delivered with cryoprecipitate. Six of the 9 dogs treated with FFP experienced adverse effects ranging from mild pruritus to pallor and weakness, whereas none of the 9 dogs treated with cryoprecipitate had any observable adverse reactions (P = .009). Based on its efficacy and safety, we recommend cryoprecipitate over FFP for treatment or prophylaxis of hemorrhagic episodes in dogs with vWD or hemophilia A.

Screening for von Willebrand Disease With a New Analyzer Using High Shear Stress: A Study of 60 Cases

We have evaluated the performance of a new analyzer using high shear stress, the PFA-100 (Platelet Function Analyzer, Dade International, Massy, France), for screening of patients with von Willebrand disease (vWD). Whole citrated blood is aspirated through a capillary to the central aperture of a membrane coated with collagen and with a platelet agonist (either epinephrine or adenosine diphosphate [ADP]). The time required to obtain occlusion of the aperture by a platelet plug is defined as the closure time (CT). We studied 60 patients with different types of vWD and 96 normal subjects. Fourteen subjects with hemophilia and 15 patients with a platelet disorder were also analyzed. When omitting results from two patients with type 2N, the 58 other patients with type 1, type 2A, type 2B, type 3, or acquired vWD all exhibited an abnormal occlusion with collagen-ADP (sensitivity, 100%) and 56 of 58 had an abnormal CT with collagen-epinephrine (sensitivity, 96.5%). Only two patients with mild type 1 were not detected with collagen-epinephrine. In comparison, the bleeding time (BT) was normal in 20 patients: 17 with type 1, two with type 2A, and one with acquired vWD (sensitivity, 65.5%). The specificity of the PFA-100 was over 95% with both types of cartridges. Thus, the analyzer is well adapted to routine testing, as it has the advantages of simplicity and ease of execution, and demonstrates a high sensitivity, clearly superior to that of BT, for the screening of patients with vWD.

Platelet function and immunologic parameters in von Willebrand's disease following cryoprecipitate and factor VIII concentrate infusion

Results of functional and immunologic tests of factor VIII and of platelet function were followed in two patients with severe von Willebrand's disease who were given cryoprecipitate during preparation for surgery. Initial correction of factor VIII coagulant activity was found to persist from 48 to 72 hours. Correction of immunologically measured factor VIII persisted for 48 hours and correlated with the patients' platelet response to ristocetin aggregation. Bleeding times were corrected for only 6 to 8 hours and showed fairly good correlation with the ristocetin aggregation factor, as suggested by Weiss. The administration of commercial factor VIII concentrate corrected all parameters except the bleeding time and the ristocetin aggregation factor measurement.