INTRODUCTION
Hemophilia A (HA) is a recessive hemorrhagic disease linked to the X chromosome, characterized by reduced levels of clotting factor VIII (FVIII). According to factor VIII levels, HA is classified as severe (less than 1%), moderate (1-5%) or mild (6-30%). In severe and moderate forms, the disease is characterized by hemorrhagic episodes on the joints (i.e., hemarthrosis), soft tissues and muscles after minor trauma or even spontaneously (1). Although the lack of FVIII is the main factor predisposing to the disease, the differences in bleeding phenotype could be related to several factors that may influence clinical presentation and response to treatment in patients with HA (2).
Among these factors, the role of platelets and their associated microvesicles expressing tissue factor on their membrane has been considered to be important (3). Moreover, several studies have also reported alterations in platelet function that challenged the classical view maintaining that platelet function is normal in hemophilic patients (4-5). However, the association between platelet function and HA is far from clear and a recent review has discussed the possible existence of a publication bias to favor only publication of studies with positive results (6).
The present work is directed to the investigation of some modulating factors of the hemorrhagic phenotype in patients with severe HA treated under the regimen of prophylaxis. Among the modulating factors that we are going to study are the platelets and microvesicles. The main objective of the study is to analyze if the administration of FVIII modifies this hemorrhagic phenotype, comparing a baseline sample (washing period / 72h without factor VIII) with respect to a sample 15 minutes after administration of FVIII.