Percentage of platelet aggregates and macroplatelets: a potential useful laboratory parameters for predicting bleeding in von Willebrand disease type 2B (VWD2B) with the p.Val1316Met mutation.

Toronto

Congreso; XXV Congress of the International Society on Thrombosis and Haemostasis; 2015

ISTH

Percentage of platelet aggregates and macroplatelets: a potential useful laboratory parameter for predicting bleeding in von Willebrand disease type 2B (VWD2B) with the p.Val1361Met mutationGuglielmone HA1,2, Smith N3, Minoldo S1, Jarchum GD1, White Adams T3 and Di Paola J3. 1 Laboratorio de Hematología, Sanatorio Allende, Córdoba; 2 Departamento de Bioquímica Clínica(CIBICI-CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina; 3School of Medicine, Department of Pediatrics, University of Colorado, USA.Background: VWD Type 2B is an autosomal dominant bleeding disorder caused by a gain-on-function mutation in the A1 domain of von Willebrand factor (VWF). The bleeding phenotype observed in these patients may be due to the combination of a low platelet count and the presence of abnormal VWF. Aims: We present here a large Argentinean family with VWD2B caused by the p.Val1361Met mutation and macrothrombocytopenia and propose a relationship between the percentage of macroplatelet and platelet aggregates with bleeding score.Materials and methods: The percentage of macroplatelets was calculated on May-Grünwald-Giemsa stained peripheral blood films in three different blood samples from each patient by the same expert operator. Platelet aggregates were quantified in the same way and arbitrarily separated into three groups a) small aggregates containing 2-3platelets, b) medium aggregated containing 4-6 platelets and c) large aggregates containing > 6 platelets.Results: The percentage of macroplatelets in the index case and his daughter were 35 and 37% when compared to other affected members (his father and two brothers) that showed 19, 25 and 30% respectively. Moreover, these two patients also showed a higher percentage of large platelet aggregates when compared to the rest of the affected family members. Interestingly, in a high percentage (> 75%) of platelet aggregates, small, medium or large, no macroplatelets were observed indicating a preference for normal size platelets to form aggregates. When compared to the bleeding scores (ISTH-BAT), the patients with the higher number of macroplatelets and aggregates exhibited higher bleeding scores suggesting a direct correlation.. Discussion: Our results in this family with VWD Type 2B due to p.Val1361Met suggest that the percentage of macroplatelet and platelet aggregates are associated with increased bleeding tendency. Larger studies in other families will be necessary to confirm these preliminary findings