Abnormal whole blood thrombi in humans with inherited platelet receptor defects

Point-of-Care Testing in Patients with Hereditary Disorders of Primary Hemostasis: A Narrative Review

Inherited disorders of primary hemostasis, such as von Willebrand disease and congenital platelet disorders, can cause extensive, typically mucocutaneous bleeding. Assays to diagnose and monitor these disorders, such as von Willebrand factor activity assays and light transmission aggregometry, are performed in specialized hemostasis laboratories but are commonly not available in local hospitals. Due to the complexity and relative scarcity of these conventional assays, point-of-care tests (POCT) might be an attractive alternative in patients with hereditary bleeding disorders. POCTs, such as thromboelastography, are increasingly used to assess hemostasis in patients with acquired hemostatic defects, aiding clinical decision-making in critical situations, such as during surgery or childbirth. In comparison, the use of these assays in patients with hereditary hemostasis defects remains relatively unexplored. This review aims to give an overview of point-of-care hemostasis tests in patients with hereditary disorders of primary hemostasis. A summary of the literature reporting on the performance of currently available and experimental POCTs in these disorders is given, and the potential utility of the assays in various use scenarios is discussed. Altogether, the studies included in this review reveal that several POCTs are capable of identifying and monitoring severe defects in the primary hemostasis, while a POCT that can reliably detect milder defects of primary hemostasis is currently lacking. A better understanding of the strengths and limitations of POCTs in assessing hereditary defects of primary hemostasis is needed, after which these tests may become available for clinical practice, potentially targeting a large group of patients with milder defects of primary hemostasis.

Point-of-care blood coagulation assay enabled by printed circuit board-based digital microfluidics

The monitoring of coagulation function has great implications in many clinical settings. However, existing coagulation assays are simplex, sample-consuming, and slow in turnaround, making them less suitable for point-of-care testing. In this work, we developed a novel blood coagulation assay that simultaneously assesses both the tendency of clotting and the stiffness of the resultant clot using printed circuit board (PCB)-based digital microfluidics. A drop of blood was actuated to move back and forth on the PCB electrode array, until the motion winded down as the blood coagulated and became thicker. The velocity tracing and the deformation of the clot were calculated via image analysis to reflect the coagulation progression and the clot stiffness, respectively. We investigated the effect of different hardware and biochemical settings on the assay results. To validate the assay, we performed assays on blood samples with hypo- and hyper-coagulability, and the results confirmed the assay's capability in distinguishing different blood samples. We then examined the correlation between the measured metrics in our assays and standard coagulation assays, namely prothrombin time and fibrinogen level, and the high correlation supported the clinical relevance of our assay. We envision that this method would serve as a powerful point-of-care coagulation testing method.

Viscoelastic testing in benign hematologic disorders: Clinical perspectives and future implications of point-of-care testing to assess hemostatic competence

Viscoelastic tests (VETs) have been used routinely for liver transplantation, cardiac surgery, and trauma, but only recently have found clinical utility in benign hematologic disorders. Therefore, guidelines for diagnosis and treatment of these disorders based on viscoelastic variables have been adapted from the existing transplant, cardiothoracic surgery, and trauma resuscitation literature. As a result, diagnostic and therapeutic strategies for benign hematologic disorders utilizing VETs are not uniform. Accordingly, even though there has been a recent increase in the utilization of VET for the diagnosis and treatment of such disorders, the literature is still in its early stages. Analysis of point-of-care viscoelastic tracings from benign hematologic disorders has the potential to allow prompt recognition of disease and to guide patient-specific intervention. Here we present a review describing the application of VETs to benign hematologic disorders.

Platelet Phenotyping and Function Testing in Thrombocytopenia

Patients who suffer from inherited or acquired thrombocytopenia can be also affected by platelet function defects, which potentially increase the risk of severe and life-threatening bleeding complications. A plethora of tests and assays for platelet phenotyping and function analysis are available, which are, in part, feasible in clinical practice due to adequate point-of-care qualities. However, most of them are time-consuming, require experienced and skilled personnel for platelet handling and processing, and are therefore well-established only in specialized laboratories. This review summarizes major indications, methods/assays for platelet phenotyping, and in vitro function testing in blood samples with reduced platelet count in relation to their clinical practicability. In addition, the diagnostic significance, difficulties, and challenges of selected tests to evaluate the hemostatic capacity and specific defects of platelets with reduced number are addressed.

Recognition of Plasminogen Activator Inhibitor Type 1 as the Primary Regulator of Fibrinolysis

The fibrinolytic system consists of a balance between rates of plasminogen activation and fibrin degradation, both of which are finely regulated by spatio-temporal mechanisms. Three distinct inhibitors of the fibrinolytic system that differently regulate these two steps are plasminogen activator inhibitor type-1 (PAI-1), α2-antiplasmin, and thrombin activatable fibrinolysis inhibitor (TAFI). In this review, we focus on the mechanisms by which PAI-1 governs total fibrinolytic activity to provide its essential role in many hemostatic disorders, including fibrinolytic shutdown after trauma. PAI-1 is a member of the serine protease inhibitor (SERPIN) superfamily and inhibits the protease activities of plasminogen activators (PAs) by forming complexes with PAs, thereby regulating fibrinolysis. The major PA in the vasculature is tissue-type PA (tPA) which is secreted from vascular endothelial cells (VECs) as an active enzyme and is retained on the surface of VECs. PAI-1, existing in molar excess to tPA in plasma, regulates the amount of free active tPA in plasma and on the surface of VECs by forming a tPA-PAI-1 complex. Thus, high plasma levels of PAI-1 are directly related to attenuated fibrinolysis and increased risk for thrombosis. Since plasma PAI-1 levels are highly elevated under a variety of pathological conditions, including infection and inflammation, the fibrinolytic potential in plasma and on VECs is readily suppressed to induce fibrinolytic shutdown. A congenital deficiency of PAI-1 in humans, in turn, leads to life-threatening bleeding. These considerations support the contention that PAI-1 is the primary regulator of the initial step of fibrinolysis and governs total fibrinolytic activity.

Thromboelastography with Platelet Studies (TEG® with PlateletMapping®) After Rattlesnake Envenomation in the Southwestern United States Demonstrates Inhibition of ADP-Induced Platelet Activation As Well As Clot Lysis

INTRODUCTION

Hematologic effects of North American rattlesnake envenomation can include fibrinogenolysis and thrombocytopenia, depending on species, geography, and other variables. During treatment, these effects are routinely monitored through assessment of fibrinogen concentrations and platelet counts. However, these tests provide no information about fibrinolysis or platelet dysfunction, both of which can also occur with venom from some species.

METHODS

This was a retrospective chart review of patients admitted to a quaternary care academic hospital (Banner - University Medical Center Phoenix) in the southwestern United States for treatment of rattlesnake envenomation, over an approximately 1-year period from March 2017 through April 2018. Patients who had thromboelastography with platelet studies (TEG® with PlateletMapping®) during their care were included.

RESULTS

Twelve patients were identified for this study. Four patients exhibited inhibition of ADP-induced platelet activation: one had normal fibrinogen and platelet count, two had concurrent hypofibrinogenemia, and one had concurrent thrombocytopenia. Crotalidae polyvalent immune Fab (ovine) reversed platelet inhibition in the single patient for whom serial thromboelastographs were available. Fibrinolysis was present in seven patients and resolved in the two patients with serial thromboelastographs.

CONCLUSIONS

Inhibition of ADP-induced platelet aggregation and fibrinolysis occurred independent of hypofibrinogenemia and thrombocytopenia, indicating fibrinogen concentration (or protime) and platelet count monitoring alone is insufficient to assess the extent of hematologic toxicity in rattlesnake envenomation. Crotalidae polyvalent immune Fab (ovine) reversed platelet inhibition in one case, suggesting platelet inhibition could also be used in treatment decisions. Fibrinolysis could also be reversed, although the timing to antivenom administration was less clear.

Platelets retain inducible alpha granule secretion by P-selectin expression but exhibit mechanical dysfunction during trauma-induced coagulopathy

Essentials Platelets in trauma-induced coagulopathy (TIC) are impaired, but the mechanism is not known. We performed comprehensive longitudinal platelet function testing in trauma patient samples. Platelets in TIC are widely impaired early after injury, but platelet activatability is intact. This suggests a mechanism of transient platelet cytoskeletal/integrin dysfunction during TIC. SUMMARY: Background Trauma-induced coagulopathy (TIC) is a common and deadly bleeding disorder. Platelet dysfunction is present during TIC, but its mechanisms remain unclear. Platelets are currently thought to become "exhausted," a state in which they have released their granule contents and can no longer aggregate or contract. Methods This prospective observational cohort study tested the hypothesis that platelet exhaustion is present during TIC and characterized the early time course of platelet dysfunction. Blood was collected from 95 adult trauma patients at a Level I trauma center at time of Emergency Department arrival and several time points over 72 h. Platelet activation state and function were characterized using CD62P (P-selectin) and PAC-1 surface membrane staining, platelet function analyzer (PFA-100), aggregometry, viscoelastic platelet mapping, and, to test for exhaustion, their ability to express CD62P after ex vivo adenosine diphosphate (ADP) agonism. Platelet function was compared between patients with and without TIC, defined by prothrombin time ≥18 s. Results Platelets in TIC showed no initial increase in their level of surface activation markers or impairment of their capacity to express CD62P in response to ADP stimulation. However, TIC platelets were impaired in nearly all functional assays, spanning adhesion, aggregation, and contraction. These effects largely remained after controlling for platelet count and fibrinogen concentration and resolved after 8 h. Conclusion The TIC platelets exhibit early impairment of adhesion, aggregation, and contraction with retained alpha granule secretion ability, suggesting a specific mechanism of cytoskeletal or integrin dysfunction that is not a result of more general platelet exhaustion.

Cryopreservation of buffy coat-derived platelet concentrates photochemically treated with amotosalen and UVA light

BACKGROUND

Cryopreserved platelets (CPPs) are considered a promising approach for extended platelet storage, bridging inventory shortages of conventionally stored platelets. It is unknown if platelet concentrates exposed to photochemical treatment (PCT) with amotosalen and ultraviolet A (UVA) light, to inactivate pathogens, are suitable for freezing. The objective of this study was to analyze potential effects of PCT on CPPs as compared with untreated CPPs.

STUDY DESIGN AND METHODS

A total of 12 PCT-treated and 12 untreated platelet units from buffy coats were cryopreserved at -80°C in 5% dimethyl sulfoxide. CPPs of both types were rapidly thawed at 37°C and resuspended in 200 mL fresh plasma. In vitro properties were analyzed prefreezing, postfreezing and thawing, and on Day 1 after thawing.

RESULTS

Directly after thawing, no major differences in platelet content, lactase hydrogenase, adenosine triphosphate, mitochondrial membrane potential, CD62P, CD42b, and platelet endothelial cell adhesion molecule were seen between PCT-CPPs and conventional CPPs. Agonist-induced PAC-1 expression and contribution of CPPs to blood coagulation in an experimental rotational thromboelastometry setup were also similar between the groups. On Day 1 after thawing, the CPPs of both types performed less well. The PCT-CPPs tended to be more affected by the freezing process than the conventional CPPs.

CONCLUSIONS

PCT-CPPs appeared slightly more susceptible to lesion effects by freezing than conventional CPPs, in particular in assays on Day 1 after thawing, but these differences were small relative to the dramatic effects of the freezing process itself.

An overview of platelet indices and methods for evaluating platelet function in thrombocytopenic patients

Thrombocytopenia is associated with bleeding risk. However, in thrombocytopenic patients, platelet count does not correlate with bleeding risk and other factors are thus likely to contribute to this risk. This review presents currently available platelet-related markers available on automated haematology analysers and commonly used methods for testing platelet function. The test principles, advantages and disadvantages of each test are described. We also evaluate the current literature regarding the clinical utility of the test for prediction of bleeding in thrombocytopenia in haematological and oncological diseases. We find that several platelet-related markers are available, but information about the clinical utility in thrombocytopenia is limited. Studies support that mean platelet volume (MPV) can aid diagnosing the cause of thrombocytopenia and low MPV may be associated with bleeding in thrombocytopenia. Flow cytometry, platelet aggregometry and platelet secretion tests are used to diagnose specific platelet function defects. The flow cytometric activation marker P-selectin and surface coverage by the Cone-and-Plate[let] analyser predict bleeding in selected thrombocytopenic populations. To fully uncover the clinical utility of platelet-related tests, information about the prevalence of platelet function defects in thrombocytopenic conditions is required. Finally, knowledge of the performance in thrombocytopenic samples from patients is essential.