Recently we reported data suggesting that platelets could compensate for the bleeding phenotype in severe haemophilia A (HA). The aim of this study was to confirm these results in a larger population with a detailed characterisation of clinical phenotype. Patients with diagnostic severe HA (FVIII:C <1%) were scored for clinical phenotype by integrating data on age at first joint bleed, joint damage, bleeding frequency and FVIII consumption. Phenotype was defined as onset of joint bleeding-score + arthropathy-score + joint bleeding-score + (2* treatment intensity-score). After a washout period of three days, blood was collected for measurement of basal level of platelet activation, platelet reactivity, endothelial cell activation and presence of procoagulant phospholipids in plasma. Thirty-three patients with severe HA were included, 13 patients with a mild, 12 patients with an average and eight patients with a severe clinical phenotype. No relevant differences in basal level of platelet activation, platelet reactivity, endothelial cell activation and procoagulant phospholipids between all three groups were observed. The mean annual FVIII consumption per kg did not correlate with the platelet P-selectin expression and glycoprotein (GP)IIbIIIa activation on platelets. In conclusion, variability in clinical phenotype in patients with diagnostic severe HA is not related to platelet activation or reactivity, measured as platelet degranulation and platelet GPIIbIIIa opening.
Keywords: GPIIbIIIa; Haemophilia A; P-selectin; clinical phenotype; platelet reactivity.