A pilot study evaluating the ex vivo effects of varying factor VIII concentration on clot kinetics and architecture in patients with haemophilia A

Abstract

BACKGROUND : Haemophilia A (HA) is a bleeding disorder, due to a deficiency in factor VIII (FVIII). These patients are unable to produce a stable fibrin clot in the propagation phase of coagulation as they do not generate sufficient thrombin. The primary treatment for HA in South Africa remains replacement therapy with standard half-life FVIII clotting factor concentrate, aimed at reducing bleeding episodes. OBJECTIVES : To evaluate the effect of varying concentrations of FVIII on whole blood (WB) clot architecture and kinetics during clot formation in patients with severe HA. DESIGN : A cross-sectional study where blood from 20 patients with HA was exposed to FVIII ex vivo and compared to a control group of 20 healthy individuals. METHODS : Scanning electron microscopy (SEM) was used to study WB clot architecture and thromboelastography® (TEG®) was used to quantify WB clot kinetics. RESULTS : Scanning electron microscopy studies revealed that patients with HA have sparse, disorganized fibrin networks with limited crosslinking and red blood cells (RBCs) stacked in rouleaux formation. Haemophilia A blood spiked to a 10 to 15 IU/dL FVIII concentration showed improvements in the organisation of the fibrin network with some altered RBCs. In addition, blood spiked to a 30 to 35 IU/dL FVIII concentration showed an increase in fibrin formation with normal RBCs. Thromboelastography® showed that patients with HA had an increased clot initiation time and decreased clot strength. When spiked to a 10 to 15 IU/dL FVIII concentration the clot kinetic profile showed normalization. However, an increase in FVIII concentration higher than 30 IU/dL showed altered clot architecture and kinetics. CONCLUSION : Based on the current study, FVIII levels at 10 to 15 IU/dL improved clot kinetics but did not normalize the architecture. It may be sufficient for prevention of haemorrhages. Factor VIII levels at 30 to 35 IU/dL resulted in rapid but weaker clot formation. However, at this concentration the clot architecture was normalised which is important for haemostasis. Here it was also evident that the findings of these two modalities (TEG® and SEM) should not be separated but interpreted in conjunction with each other.