thromboplastin and Purpura--Thrombocytopenic--Idiopathic

Topics: Ad26COVS1; Autoantibodies; Blood Coagulation; Blood Platelets; Cell-Derived Microparticles; ChAdOx1 nCoV-19; COVID-19 Vaccines; Female; Humans; Male; Middle Aged; Phosphatidylserines; Platelet Factor 4; Purpura, Thrombocytopenic, Idiopathic; Receptors, IgG; Risk Factors; Sinus Thrombosis, Intracranial; Thromboplastin; Vaccination

Haemostatic treatment modalities alternative to platelet transfusion are desirable to control serious acute bleeds in primary immune thrombocytopenia (ITP). This study challenged the hypothesis that recombinant activated factor VII (rFVIIa) combined with fibrinogen concentrate may correct whole blood (WB) clot formation in ITP. Blood from ITP patients (n = 12) was drawn into tubes containing 3·2% citrate and corn trypsin inhibitor 18·3 μg/ml. WB [mean platelet count 22 × 10(9) /l (range 0-42)] was spiked in vitro with buffer, donor platelets (+40 × 10(9) /l), rFVIIa (1 or 4 μg/ml), fibrinogen (1 or 3 mg/ml), or combinations of rFVIIa and fibrinogen. Coagulation profiles were recorded by tissue factor (0·03 pmol/l) activated thromboelastometry. Coagulation in ITP was characterized by a prolonged clotting time (CT, 1490 s (mean)) and a low maximum velocity (MaxVel, 3·4 mm × 100/s) and maximum clot firmness (MCF, 38·2 mm). Fibrinogen showed no haemostatic effect, whereas rFVIIa reduced the CT and increased the MaxVel. The combination of fibrinogen and rFVIIa revealed a significant synergistic effect, improving all parameters (CT 794 s, MaxVel 7·9 mm × 100/s, MCF 50·7 mm) even at very low platelet counts. These data suggest that rFVIIa combined with fibrinogen corrects the coagulopathy of ITP even at very low platelet counts, and may represent an alternative to platelet transfusion.

Topics: Adult; Aged; Blood Coagulation; Drug Evaluation, Preclinical; Drug Synergism; Factor VIIa; Female; Fibrinogen; Humans; Immunoglobulins, Intravenous; In Vitro Techniques; Male; Middle Aged; Platelet Aggregation; Platelet Count; Platelet-Rich Plasma; Purpura, Thrombocytopenic, Idiopathic; Receptors, Fc; Recombinant Fusion Proteins; Recombinant Proteins; Thrombelastography; Thrombin; Thromboplastin; Thrombopoietin

Platelets contribute to hemostasis by forming a platelet plug and by providing a procoagulant surface for the assembly and activation of the coagulation factors. The contribution of platelets to prothrombotic disorders has been difficult to analyze. Recently an assay was reported that measured the procoagulant activity of test platelets by making the platelet lipid surface the limiting factor in the production of thrombin. In this report we describe a novel technique, based on this assay, that we used to study patient serum factors that activate control platelets and in turn initiate measurable procoagulant activity. Using this assay we investigated a group of patients with prothrombotic disorders. The patient test serum was incubated with normal platelets in the presence of activated factor Xa. The resultant thrombin was measured in a chromogenic assay. The rate-limiting step was the presence of any potential platelet-activating factors, such as antibodies in the heat-treated test serum, that would allow the Xa to bind to the platelet phospholipid surface. Serum samples from patients with heparin-induced thrombocytopenia (HIT) and the anti-phospholipid antibody syndrome enhanced platelet procoagulant activity, while samples from patients with idiopathic thrombocytopenic purpura and disseminated intravascular coagulation (DIC) did not. HIT serum samples also induced platelet activation, as measured by platelet microparticle shedding, carbon 14-labeled serotonin release, and platelet aggregation. The measurement of serum-induced platelet procoagulant activity provides a method for the investigation of circulating platelet agonists in prothrombotic disorders.

Topics: Antiphospholipid Syndrome; Blood Coagulation Factors; Blood Platelets; Disseminated Intravascular Coagulation; Factor Xa; Heparin; Humans; Platelet Activation; Platelet Aggregation; Prothrombin; Purpura, Thrombocytopenic, Idiopathic; Serotonin; Thrombin; Thromboplastin