Showing papers in "Seminars in Thrombosis and Hemostasis in 2008"

Clinical Utility of the PFA-100

Abstract: The PFA-100 (platelet function analyzer) is a relatively new tool for the investigation of primary hemostasis. This article reviews the history of the PFA-100 and details its clinical utility in several settings. The PFA-100 was first introduced to us in 1995 in an issue of Seminars in Thrombosis And Hemostasis, which included data from a field trial headed by Dr. Eberhard Mammen. Since that time, the PFA-100 has featured in nearly 500 publications and some 35 reviews. The PFA-100 has potential utility in monitoring antiplatelet therapy (including aspirin) and as a screening tool for investigating possible von Willebrand disease (VWD) and various platelet disorders. The PFA-100 also has potential value for monitoring DDAVP (desmopressin) therapy in both VWD and functional platelet disorders. Most recent attention has focused on sensitivity to antiplatelet medication, where a new language has also emerged, with researchers talking about "aspirin resistance," "aspirin responsiveness," and "aspirin nonresponsiveness." Ultimately, the greatest strengths of the PFA-100 are its simplicity in use and excellent sensitivity to various hemostatic disturbances. However, because it is a "global" test system for primary hemostasis, this also creates a significant limitation because the PFA-100 is not specific for, nor predictive of, any particular disorder. However, used appropriately, the PFA-100 can be considered a worthwhile addition to hemostasis laboratories involved in the identification or therapeutic monitoring of primary hemostatic disorders. The potential future applications for this simple instrument are also briefly assessed.

Antiphospholipid antibodies and the antiphospholipid syndrome: pathogenic mechanisms.

Abstract: Antiphospholipid antibodies (Abs) are associated with thrombosis and are a risk factor for recurrent pregnancy loss and obstetric complications in patients with the antiphospholipid syndrome. It is generally accepted that the major autoantigen for aPL Abs is beta (2) glycoprotein I, which mediates the binding of aPL Abs to target cells (i.e., endothelial cells, monocytes, platelets, trophoblasts, etc.) leading to thrombosis and fetal loss. This article addresses molecular events triggered by aPL Abs on endothelial cells, platelets, and monocytes and complement activation, as well as a review of the current knowledge with regard to the putative receptor(s) recognized by aPL Abs on target cells as well as novel mechanisms that involve fibrinolytic processes. A section is devoted to the description of thrombotic and inflammatory processes that lead to obstetric complications mediated by aPL Abs. Based on experimental evidence using in vitro and in vivo models, new targeted therapies for treatment and/or prevention of thrombosis and pregnancy loss in antiphospholipid syndrome are proposed.

Preanalytical and postanalytical variables: the leading causes of diagnostic error in hemostasis?

Abstract: The advent of modern instrumentation, with associated improvements in test reliability, together with appropriate internal quality control and external quality assurance measures, has led to substantial reduction in analytical errors within hemostasis laboratories. Unfortunately, the reporting of incorrect or inappropriate test results still occurs, perhaps even as frequently as in the past. Many of these cases will arise due to a variety of events largely outside the control of the laboratories performing the laboratory tests and primarily comprise preanalytical events related to patient collection and sample processing and postanalytical events related to the reporting and interpretation of test results. The current article provides an overview of these events and provides some suggestions on how they can be minimized or prevented to ensure that the test results the clinician receives actually represent the true clinical status of the patient under investigation rather than just reflecting the status of an (inappropriate) clinical sample received and tested. This article should be of interest to both laboratory scientists working in hemostasis and the clinicians that request such tests. The former, because these are ultimately responsible for the test results they provide to clinicians, and there is a duty of care to provide both accurate and precise results to enable clinicians to manage patients appropriately and to avoid the need to recollect and retest. The latter because unless clinicians gain an appreciation of these issues, they will not be in a position to best manage their patients.

Alterations of hemostasis associated with malignancy: etiology, pathophysiology, diagnosis and management.

Abstract: As outlined in this paper, the patient with disseminated malignancy suffers many alterations of hemostasis; in addition, hemorrhage or less commonly thrombosis is the final clinical event in many of these patients. Patients with malignancy present a major clinical challenge in this day of new oncological awareness and more aggressive care. Thus, it is important to realize that these alterations of hemostasis do exist and they must be approached in a logical manner with respect to diagnosis as well as efficacious therapy. By far the most common alteration of hemostasis in malignancy is that of hemorrhage associated with thrombocytopenia either drug-induced or from bone marrow invasion. However, hemorrhage due to disseminated intravascular coagulation is also quite common. In addition, many antineoplastic drugs, as well as radiotherapy, may lead to hemorrhage in these patients. Thrombosis, which is also commonly seen in the patient with malignancy, is usually a manifestation of disseminated intravascular coagulation manifest as an intravascular thrombotic rather than an intravascular proteolytic event. When suspecting this, confirmatory laboratory evidence must be sought and the patient treated apropriately. When approaching the patient with malignancy and either hemorrhage or thrombosis, all of the potential defects in hemostasis must be taken into account, defined from the laboratory standpoint, and treated in as precise a manner as possible.

Pathogenesis of Venous Thromboembolism: When the Cup Runneth Over

Abstract: A comprehensive understanding of the pathogenesis of venous thrombosis is essential for identifying patients at increased risk and who may therefore benefit from more aggressive preventive and therapeutic measures. As for other pathologies, the pathogenesis of venous thromboembolism is multifactorial. All risk factors, either congenital or acquired, are relatively "innocent" when considered alone. However, when an individual is unlucky enough to inherit one or more abnormality, compounded in many cases by environmental hazards, that person may be propelled over a threshold that precipitates the development of thrombosis. An appropriate analogy is that where "the last drop makes the cup run over." A reinterpretation of the traditional Virchow's triad (abnormal vessel wall, abnormal blood flow, and abnormal blood constituents) was provided by Eberhard Mammen throughout his research, and this has contributed greatly to the understanding of the pathogenesis of this serious disorder. Mammen postulated immobility as the leading event, because it reduced blood flow as a result of decreased muscle contraction. The subsequent "stasis of flow" led to accumulation of blood within the intramuscular sinuses, especially of the calf, triggering hypercoagulability due to local accumulation of activated clotting factors and coagulation activation products and the simultaneous consumption of blood coagulation inhibitors. On Mammen's "hit list" nearly 20 years ago were included (among inherited abnormalities) decreased protein C, protein S, antithrombin III, plasminogen, and tissue plasminogen activator, and increased plasminogen activator inhibitor-1, whereas (among acquired predisposing conditions) surgery, trauma, previous thromboembolism, prolonged immobility and paralysis, malignancy, congestive heart failure, obesity, advanced age, pregnancy and puerperium, varicose veins, and oral contraceptives were also identified. Some two decades later, the situation has perhaps not changed so much, although studies continue to expand our knowledge of this topic, clarifying the relative contribution of each single risk factor in the pathogenesis of venous thrombosis.

Idiopathic thrombocytopenic purpura in children.

Abstract: ITP in childhood is most often of the acute, self-limited variety, with spontaneous recovery occurring within a matter of days or weeks. In many of these children, acute thrombopenic purpura follows in the wake of a viral infection. While the pathogenesis is not entirely clear, it seem probable that the platelet membrane is altered by virus or by soluble viral antigen-antibody complexes; platelets thus damaged become susceptible to rapid destruction by the RES. Management remains somewhat controversial. While almost all agree that corticosteroid should not be used in all cases of acute childhood purpura, there are still no clear-cut indications for their use, and no real evidence that they are of benefit in reducing the risk of the one rare but serious complication of childhood ITP, namely, intracranial hemorrhage (ICH). In approximately 5-10% of children, ITP ultimately proves to be of the chronic variety, and is in all probability the same condition that is seen in adults. Splenectomy is the treatment of choice, Another small subgroup of children have ITP of the recurrent acute variety; there is some evidence that this entity may also have an autoimmune pathogenesis. Infants born to mothers who have (or have had) ITP often manifest thrombopenia, with or without purpura and other bleeding. While this is generally a benign, self-limited process, requiring no treatment, ICH occurs in a small but significant number of affected infants and probably results from head trauma during delivery.

Coagulation abnormalities in liver disease.

Abstract: The decreased capacity of the liver to synthesize proteins is the main cause of decreased blood levels of clotting factors II, V, VII, IX, X and of antithrombin III in patients with liver disease. Therefore, determination of the activity or concentration of these coagulation proteins is a useful test of liver function and guide to prognosis, provided that other mechanisms which may influence the blood level are carefully considered. Clotting factor assays have an only limited value for the differential diagnosis in liver disease.

Prevention of venous thromboembolism.

Abstract: Of the various prophylactic agents evaluated, four have been found to be effective. These are oral anticoagulants, low-dose heparin, mechanical devices which increase venous blood-flow in the leg, and Dextran. Oral anticoagulants have been shown to be effective in patients having abdominal, thoracic, or hip surgery, when treatment was started either before surgery or in the immediate postoperative period. They have also been shown to be effective in medical patients. The evidence derives from studies which showed that treatment can reduce total mortality, prevents venous thromboembolism detected clinically or at autopsy, and prevents thrombosis diagnosed with venography. On the other hand, the incidence of thrombosis diagnosed by 125I-fibrinogen scanning was not reduced when oral anticoagulants were started just before or just after surgery. This suggests that oral anticoagulant treatment starting in the immediate postoperative period may not prevent formation of the initial thrombotic nidus, but is clinically effective because it prevents extension of the nidus to form a significant thrombus. Bleeding has been a significant complication in almost all studies of surgical patients, and this is the major factor which has prevented widespread use of oral anticoagulant prophylaxis. In addition, the need for careful laboratory monitoring makes this approach inconvenient and adds to its expense. Low-dose heparin has been shown to be effective in general surgical and medical patients, but results have been inconclusive in patients having elective hip surgery, and this approach is probably ineffective in patients with hip fracture. In general surgical patients, low-dose heparin prophylaxis has been shown to prevent pulmonary embolism diagnosed at autopsy examination or with lung scanning, and calf and thigh vein thrombosis diagnosed with 125I-fibrinogen leg-scanning. A slight, but statistically significant, increase in the frequency of wound hematoma and a greater postoperative hematocrit fall have been reported when heparin was given three times daily, but not with the twice daily heparin injection regimen. In these studies, low-dose heparin was given without laboratory control of its anticoagulant effect, so that this prophylactic approach is simple, but the need for subcutaneous injections is a disadvantage of this approach. Results with methods which increase venous blood-flow in the leg have varied, depending on the technic used. Active measures, such as intermittent pneumatic calf compression or peroperative electrical calf muscle stimulation, have been shown to prevent thrombosis detected with 125I-fibrinogen leg-scanning. However, while the evidence suggests that both methods are effective in relatively low risk patients, they may have limited value in the high risk patient who is confined to bed for a long time. These methods are free of side effects and relatively inexpensive, but intermittent calf compression, in particular, is slightly cumbersome...

The role of natural anticoagulants in the pathogenesis and management of systemic activation of coagulation and inflammation in critically ill patients.

Abstract: Critically ill patients often have systemic activation of both inflammatory systems and coagulation. Increasing evidence points to an extensive cross-talk between these two systems, whereby inflammation leads to activation of coagulation and coagulation considerably affects inflammatory activity. The intricate relationship between inflammation and coagulation may have major consequences for the pathogenesis of microvascular failure and subsequent multiple organ failure, as a result of severe infection and the associated systemic inflammatory response. Molecular pathways that contribute to inflammation-induced activation of coagulation have been precisely identified. Activation of the coagulation system and ensuing thrombin generation is dependent on an interleukin-6-induced expression of tissue factor on activated mononuclear cells and endothelial cells and is insufficiently counteracted by tissue factor pathway inhibitor. Simultaneously, endothelial-bound anticoagulant mechanisms, in particular the protein C system and the antithrombin system, are shut off by proinflammatory cytokines. Modulation of inflammatory activity by activation of coagulation also occurs by various mechanisms. Activated coagulation proteases, such as the tissue factor-factor VIIa complex, factor Xa, and thrombin, can bind to protease-activated receptors on various cells, and the ensuing intracellular signaling leads to increased production of proinflammatory cytokines and chemokines. Activated protein C can bind to the protein C receptor on endothelial cells and mononuclear cells, thereby affecting NF-kappaB nuclear translocation and subsequently influencing inflammatory gene expression and inhibition of tissue factor expression on mononuclear cells. Observations in experimental models of targeted disruption of the protein C gene and restoration of the downregulated protein C pathway by administration of recombinant activated protein C support this notion.

Alterations of hemostasis associated with cardiopulmonary bypass: pathophysiology, prevention, diagnosis, and management

Abstract: This chapter has provided a review of available literature regarding alterations of hemostasis associated with CPB. The primary pathology of altered hemostasis during CPB appears to be two-fold: (1) a functional platelet defect of unclear etiology, which occurs in virtually all patients, and (2) a primary hyperfibino(geno)lytic defect which occurs in the majority of patients undergoing cardiopulmonary bypass. Significant thrombocytopenia does not appear to be a consistent problem, and is probably a function of perfusion technics; this may, however, be an important source of hemorrhage in some instances. Although hyperheparinemia, heparin rebound, and protamine excess have occasionally been incriminated as sources of hemorrhage during CPB, no well documented cases appear in the literature. Likewise, although DIC gained popularity in early reports of CPB hemorrahge, it appears that this syndrome rarely, if ever, arises as a consequence of CPB alone; it can be seen, however, in CPB patients who are provided a triggerin situation for DIC, such as shock, sepsis, or hemolytic transfusion reaction. It is likely that many reported alterations of hemostasis during CPB which were concluded to represent DIC actually were due to hyperfibino(geno)lysis. The key to prevention of CPB hemorrhage rests simply in obtaining an adequate preoperative workup. Of extreme importance is an adequate history with respect to bleeding tendencies in both patient and family; of equal importance is a careful history regarding antiplatelet drugs. A careful physical examination, searching for clues of a real or potential bleeding diathesis, also can often prevent catastrophic cases of CPB hemorrhage. Lastly, an adequate presurgical laboratory screen must be performed; in addition to the usual prothrombin time, partial thromboplastin time, and platelet count, a thrombin time and standardized template bleeding time must be added. The addition of these two simple modalities will insure against significant defects in fibrinogen, the fibrinolytic system, vascular function, and platelet function. When CPB hemorrhage occurs, simple laboratory screening will usually allow for a quick hemostasis evaluation. The parameters recommended in this review will distinguish between surgical and nonsurgical bleeding and should, therefore, allow for a quick decision regarding necessity for reexploration and the adequacy of hemostasis if reexploration is needed. In addition, this screen will distinguish between difficulties with heparin, protamine, and the fibrinolytic system. The vast majority of nonsurgical hemorrhages during CPB is due to a functional platlet defect, primary hyperfibrino(geno)lysis, or a combination of these. The quick administration of platelet concentrates, while awaiting laboratory evaluation, will control or significantly blunt most instances of CPB hemorrhage. If platelets fail to control bleeding, and reasonable laboratory evidence of primary hyperfibrino(geno)lysis is present, antifibrinolytics should then be used...

Current and future prospects for anticoagulant therapy: inhibitors of factor Xa and factor IIa.

Abstract: Indirect systemic and direct oral factor Xa and direct oral factor IIa inhibitors with improved pharmacologic profiles compared with heparins and vitamin K antagonists are currently in clinical development. This overview focuses on the indirect antithrombin dependent pentasaccharide derivatives of idraparinux and on the most advanced oral direct inhibitors to factor Xa (rivaroxaban and apixaban) and IIa (dabigatran). Specifically, the results of dose-finding studies for the prevention of venous thromboembolism after elective orthopedic surgery, the results of dose-finding studies for treatment of acute venous thromboembolism including prolonged prophylaxis of recurrent events, and the designs of ongoing clinical trials are reviewed.

Thrombocytopenia in critically ill patients.

Abstract: Critically ill patients often have a low platelet count. A proper identification of the underlying cause of this abnormality is required, because various underlying disorders may necessitate different diagnostic and therapeutic management strategies. Platelets are part of the first line of defense of the body against bleeding, hence, thrombocytopenia may increase the risk of hemorrhage. In case of systemic inflammatory syndromes, such as the response to sepsis, disseminated intravascular platelet activation may occur, which will contribute to microvascular failure and thereby play a role in the development of organ dysfunction. A low platelet count is a strong and independent predictor of an adverse outcome in critically ill patients, thereby facilitating a simple and practical risk assessment in these patients and potentially guiding the use of complex or expensive treatment strategies.

Standardization and clinical utility of thrombin-generation assays.

Abstract: Thrombin generation is a key process that determines the extent of a hemostatic plug or a thrombotic process. The ensuing thrombin burst is crucial for the formation of a stable fibrin clot. During its active life, thrombin exerts a multitude of highly regulated actions on the blood and the vessel wall, including the clotting of fibrinogen. The inappropriate generation of thrombin may lead to pathologic processes, foremost of which are hemorrhagic or thrombotic diseases. The coagulation system is usually investigated by means of two in vitro classic clotting tests, the activated partial thromboplastin time (APTT) and prothrombin time (PT), which assess only time to initiation of clot formation and do not entirely reflect global hemostatic balance. The APTT and PT permit identification of connectivity between the component activities identified as required for plasma coagulation and define the concept of intrinsic and extrinsic coagulation pathways, which converge at the point of formation of the prothrombinase complex. However, the mechanisms established by in vitro tests are not always mirrored in the human pathologies associated with bleeding or thrombosis. The recent development of newer tests based on the continuous registration of thrombin generation under in vitro conditions that mimic more closely what occurs in vivo prompt a reinvestigation of the balance between procoagulants and anticoagulants in patients with various hemostatic disorders. Thrombin-generation assays not only provide an overall assessment of hemostasis but also target potential extrahemostatic effects of the generated thrombin, a potent agonist of a multitude of cellular activation pathways. Moreover, estimation of an individual's thrombin-generation potential may correlate more closely with a hypercoagulable or hypocoagulable phenotype when compared with traditional coagulation tests. In this review, we discuss to what extent thrombin generation can be expected to reflect the clotting function of blood, the development and use of different thrombin-generation assay systems suitable for detecting changes in the kinetics of thrombin generation, and the clinical utility of thrombin generation.

Activated partial thromboplastin time: new tricks for an old dogma.

Abstract: The activated partial thromboplastin time (APTT) is the most common coagulation test procedure performed in routine laboratories, apart from the prothrombin time. The test is traditionally used for identifying quantitative and qualitative abnormalities in the intrinsic and common pathways of coagulation, monitoring anticoagulant therapy with unfractionated heparin, and detecting inhibitors of blood coagulation, the most common of which is the lupus anticoagulant. Whereas short APTT values have been mostly overlooked in the past, recent evidence suggests that these might be associated with hypercoagulability. Although clinical relevance is yet to be clearly defined, hypercoagulability detected by a shortened APTT appears to be significantly associated with a major risk of venous thromboembolism independently from other variables such as blood group, the presence of inherited thrombophilia, and factor VIII levels. This novel finding suggests that this traditional, simple, and inexpensive test might have renewed utility along with traditional thrombophilic tests in the evaluation of venous thromboembolic risk. In addition, APTT waveform analysis is also providing mounting evidence of added utility, in particular for identifying sepsis and disseminated intravascular coagulation in critically ill patients (particularly where this might worsen the prognosis), for monitoring therapy in patients with inhibitors, and as a diagnostic aid to identify patients with antiphospholipid antibodies. In total, such emerging evidence suggests that the APTT is either an old dogma displaying new tricks or else might describe a new dogma for an old laboratory trick.

Hemostatic abnormalities and liver diseases.

Abstract: Professor Eberhard F. Mammen greatly contributed to the understanding of the relationship between hemostatic abnormalities and liver diseases. The physiology of the hemostatic system is closely linked to liver function because the liver parenchymal cells produce most of the factors of the clotting and fibrinolytic systems. Acute or chronic hepatocellular diseases and hepatic failure including liver cirrhosis, vitamin K deficiency, liver surgery including liver transplantation, and sclerotherapy of bleeding esophageal varices, which were classified by Prof. Mammen, show various hemostatic abnormalities in the coagulation system, fibrinolytic system, platelets, and the reticuloendothelial system. Hemostatic abnormalities in patients with hepatic failure or in those that have undergone liver surgery are similar to those in disseminated intravascular coagulation. Prof. Mammen also contributed to the study of vitamin K-dependent clotting factors, antithrombin, and hemostatic molecular markers. Partly based on this work, the prothrombin time-international normalized ratio, several hemostatic molecular markers, and antithrombin therapy have been recently developed for the diagnosis and treatment of thrombosis.

Survival of heparins, oral anticoagulants, and aspirin after the year 2010.

Abstract: The conventional management of thrombotic and cardiovascular disorders is based on the use of heparin, oral anticoagulants, and aspirin. Despite remarkable progress in life sciences, these drugs still remain a challenge and a mystery to us, and their use is far from optimized. The development of low-molecular-weight heparins and the synthesis of heparinomimetics, such as the chemically synthesized pentasaccharide, represent a refined use of heparin. Additional drugs from this knowledge will continue to develop; however, none of these drugs will ever match the polypharmacology of heparin. Aspirin still remains the leading drug in the management of thrombotic and cardiovascular disorders. The newer antiplatelet drugs such as adenosine diphosphate receptor inhibitors, glycoprotein IIb/IIIa inhibitors, and other specific inhibitors have limited effects and have been tested in patients who have already been treated with aspirin. Warfarin provides a convenient and affordable approach in the long-term outpatient management of thrombotic disorders. The optimized use of these drugs still remains as the approach of choice to manage thrombotic disorders. The new anticoagulant targets, including specific sites in the hemostatic network such as tissue factor, individual clotting factors (IIa, VIIa, IXa, Xa, XIIa, and XIIIa), recombinant forms of serpins (antithrombin, heparin cofactor II, and tissue factor pathway inhibitors), recombinant activated protein C, thrombomodulin, and site-specific serine protease inhibitor complexes have also been developed. There is a major thrust on the development of orally bioavailable anticoagulant drugs (anti-Xa and anti-IIa agents), which are slated to replace oral anticoagulants. Both the anti-factor Xa and antithrombin agents have been developed for oral use and have provided impressive clinical outcomes in sponsor trials for the postsurgical prophylaxis of venous thrombosis; however, safety concerns related to liver enzyme elevations and thrombosis rebound have been reported with their use. For these reasons, the U.S. Food and Drug Administration did not approve the orally active antithrombin agent ximelagatran for several indications. The synthetic pentasaccharide (fondaparinux) has undergone an aggressive clinical development. Unexpectedly, fondaparinux also produced major bleeding problems at minimal dosages. Fondaparinux represents only one of the multiple pharmacologic effects of heparins. Thus, its therapeutic index will be proportionately narrower. The newer antiplatelet drugs have added a new dimension in the management of thrombotic disorders. The favorable clinical outcomes with aspirin and clopidogrel have validated cyclooxygenase (COX)-1 and P2Y (12) receptors as targets for new drug development. Prasugrel, a novel thienopyridine, cangrelor, and AZD 6140 represent newer P2Y (12) antagonists. Cangrelor and AZD 6140 are direct inhibitors, whereas prasugrel requires metabolic activation. Though clinically effective, recent results have prompted a closure of a large clinical trial with prasugrel due to bleeding. The newer anticoagulant and antiplatelet drugs are attractive for several reasons; however, none of these are expected to replace the conventional drugs in polytherapeutic approaches. Heparins, warfarin, and aspirin will continue to play a major role in the management of thrombotic and cardiovascular disorders beyond 2010.

Mechanisms Linking Tumor Cell–Associated Procoagulant Function to Tumor Dissemination

Abstract: There is a persuasive body of evidence suggesting that tissue factor (TF) is a major determinant of tumor progression. In addition to its "traditional" function as the initiator of hemostasis, TF may support tumor progression through signaling mechanisms involving either direct signal transduction through the TF cytoplasmic domain or TF:F VIIa-mediated and TF/F VIIa/F Xa-mediated activation of protease-activated receptors. Whereas TF-mediated signaling events uncoupled from hemostasis may play an important role in tumor dissemination in some contexts, TF-mediated thrombin generation appears to be the major mechanism linking tumor cell-associated TF to metastasis. At least one mechanism coupling thrombin generation to metastatic potential involves the most distal components of the hemostatic system (i.e., platelets, fibrinogen, and factor XIII) and leads to a restriction in natural killer cell-mediated lysis of newly formed micrometastases. A detailed understanding of the mechanisms linking TF and circulating hemostatic system components to tumor progression may lead to novel therapeutic targets for cancer treatment.

Microparticles in health and disease.

Abstract: Microparticles (MPs) are small fragments of membrane-bound cytoplasm that are shed from the surface of an activated or apoptotic cell. Recently, their function as vectors of transcellular exchange of biologic information, in addition to better described forms of intercellular communication such as growth factors, cytokines, and chemokines, has become well recognized. Circulating levels of MPs are thought to reflect a balance between cell stimulation, proliferation, and death. The production of MPs is thought to predominately occur by vesiculation or blebbing of the cell membrane. The mechanisms governing the remodeling of the plasma membrane are complex, involving cytoskeletal changes and a shift from normal phospholipid asymmetry. Increased intracellular calcium subsequent to cell activation leads to intracellular increases in several proteins including gelsolin and calpain, as well as the activity of enzymes such as translocase, floppase, and scramblase, which play important roles in the homeostasis of the cell membrane. The membrane vesiculation and phospholipids asymmetry leading to the production of MPs occurs by the complex interplay of the proteins involved. There are several clinical conditions associated with elevated MPs, and most are also associated with an increased risk of thrombosis. Apart from cardiovascular disease and venous thromboembolism, MPs are also elevated in solid tumors with metastatic disease. The measurement of MPs is being regarded as a potential biomarker, given the range of conditions in which they are elevated and the association with prothrombotic states. The utility of measuring MPs as a diagnostic and prognostic marker is currently a subject of intense investigation. The further development of the various methods for the detection and measurement of MPs and prospective clinical trials establishing the utility of such tests will be critical prior to the routine measurement of MPs in the diagnostic laboratory.

A critical review on the use of recombinant factor VIIa in life-threatening obstetric postpartum hemorrhage.

Abstract: The objective of this review was to evaluate and summarize the current literature on the unlicensed use of the novel agent recombinant activated factor VII (rFVIIa) in the management of major postpartum hemorrhage. After a systematic electronic search without temporal limits on MEDLINE, EMBASE, OVID and SCOPUS, the bibliographic references of all retrieved studies and reviews were additionally assessed for further reports of clinical trials. Unpublished works were also identified by searching abstracts from the most eminent conferences on this topic. In total, there were 31 studies that fulfilled our inclusion criteria. These studies incorporated 118 cases of massive postpartum hemorrhage treated with rFVIIa. The median age of the patients was 31.4 years, and cesarean section appeared to increase the risk of postpartum hemorrhage. At a median dose of 71.6 mug/kg, rFVIIa was reported to be effective in stopping or reducing bleeding in nearly 90% of the reported cases. Based on the evidence from the literature, we give some recommendations on the use of rFVIIa in massive postpartum hemorrhage. Nevertheless, although these reports suggest the potential role of rFVIIa in treating massive postpartum hemorrhage refractory to standard therapy, we advise particular caution in interpreting these results, as they are derived from few and uncontrolled studies. Further evidence is needed using well-designed clinical trials to better assess the optimal dose, the effectiveness, and the safety of rFVIIa in such critical bleeding conditions.

Can we predict bleeding

Abstract: The prior identification of subjects who are likely to bleed excessively when subjected to operative surgery and other invasive procedures is desirable. Frequently, reliance is placed on laboratory-based screening tests of blood coagulation for this purpose. However, published evidence does not support this approach as the tests are not fit for purpose, and their sensitivity and specificity are low. Some more global assays may have use in the diagnostic workup in subjects with hemorrhage, but none has been established to date as an efficient method for prediction of bleeding in unselected populations. There is renewed interest in the use of the clinical history for the prediction of bleeding. Recent reports suggest that when a structured questionnaire is employed to derive a bleeding score, the positive predictive value of the approach for the detection of bleeding disorders is high.

The phenotypic heterogeneity of severe hemophilia.

Abstract: It has been long recognized that 10 to 15% of patients with "phenotypically characterized" severe hemophilia (< 1% clotting factor activity) have relatively mild disease clinically. Not all these patients have frequent spontaneous bleeding, and even among those who bleed, the extent of joint damage tends to vary considerably. The basis for this difference has not been completely understood. This article reviews the literature on possible determinants of phenotypic variation in patients with severe hemophilia. Apart from the well-recognized associations of the level of residual clotting factor activity, pharmacokinetics of administered clotting factor concentrates, and presence of prothrombotic markers, there is evidence to suggest that variations in other coagulation proteins as assessed in tests of global hemostasis as well as the fibrinolytic system can affect the clinical severity of bleeding. We also hypothesize that mediators of the inflammatory response in the synovium are likely to impact the severity of joint damage in these patients. One of the major issues in the management of hemophilia today is to decide on ways in which therapy, particularly the initiation and intensity of prophylaxis, can be individualized. A detailed understanding of all factors that may contribute to joint damage in severe hemophilia could help us in tailoring therapy for these individuals.

Tissue factor-bearing microparticles and cancer.

Abstract: Blood-borne tissue factor (TF)-bearing microparticles have been shown to play an important role in thrombus propagation in experimental models. The pathophysiologic role of these microparticles is being investigated in several prothrombotic conditions including cancer-associated thrombosis. Tumor cells are known to shed TF-bearing microparticles in vitro, and circulating TF-bearing microparticles can be measured in plasma samples from patients with advanced cancer. We are currently using an impedance-based flow cytometer to accurately size and enumerate TF-bearing microparticles to explore the association between cancer thrombosis and elevations in circulating TF-bearing microparticles.

Point of care coagulation tests in critically ill patients.

Abstract: Point of care assays for various analytes have been established in critical care, including blood gas analysis, glucose, electrolytes, and markers for cardiac ischemia. Coagulation assays can also be adapted to the critical care environment by using whole blood as sample material and instruments optimized for point of care analysis. Available assays include the conventional coagulation assays, such as prothrombin time and activated partial thromboplastin time, fibrinogen, assays for monitoring of anticoagulant drugs, global coagulation assays based on thrombelastography and viscosimetry, platelet function assays, and D-dimer assays. The main problem in point of care coagulation diagnostics is quality control. Point of care coagulation assays help in rapidly establishing a diagnosis, clarifying causes of bleeding, and monitoring therapy. Thrombelastography and similar assays extend the scope of coagulation diagnostics by visualizing the process of clot formation and extending the observation period to provide an estimate of clot stability versus mechanical and proteolytic attack.

Phenotypic identification of platelet-type von Willebrand disease and its discrimination from type 2B von Willebrand disease: a question of 2B or not 2B? A story of nonidentical twins? Or two sides of a multidenominational or multifaceted primary-hemostasis coin?

Abstract: Platelet-type von Willebrand disease (PT-VWD) and type 2B von Willebrand disease (2B-VWD) have different etiologies although both present with a similar clinical bleeding and basic laboratory phenotype Both PT-VWD and 2B-VWD represent gain-of-function mutations that lead to enhanced binding between plasma von Willebrand factor (VWF) and its platelet ligand, glycoprotein Ib alpha (GP1BA) However, 2B-VWD results from a functionally abnormal VWF molecule arising from mutations in the VWF gene, whereas PT-VWD is caused by hyperresponsive platelets resulting from mutations in the platelet GP1BA gene A definitive diagnosis of PT-VWD versus 2B-VWD is critical for treatment decisions (as differential therapies might be respectively required) and also for family counseling However, laboratory discrimination of PT-VWD versus 2B-VWD is problematic because simple phenotypic testing will not permit their differentiation, and the more complex testing approaches that might permit their differentiation are rarely applied, or are perhaps poorly applied Although differential identification of PT-VWD versus 2B-VWD can most definitively be achieved by identifying the gene defect at either the VWF or GP1BA loci, such tests are not commonly available, not always successful, and even if available and successful might not be readily available to serve time-critical treatment decisions Accordingly, simple laboratory tools to enable discrimination of the two disorders would be a valuable addition to the test repertoire of the hemostasis laboratory This article provides a review of PT-VWD-related literature and an overview of a phenotypic laboratory test process that should enable the effective identification of PT-VWD and its discrimination from 2B-VWD

Recent therapeutic advances in thrombotic thrombocytopenic purpura.

Abstract: Whole plasma infusion, in our experience, has been highly effective in the management of patients with thrombotic thrombocytopenic purpura. The effectiveness of plasma infusion in the treatment of this severe disorder implies the deficiency of a factor in the patient's plasma. Furthermore, we have observed that when platelets are suspended in plasma obtained during active, untreated thrombotic purpura, aggregation occurs. This effect is neutralized by preincubation of the thrombotic thrombocytopenic purpura plasma with normal plasma. Thus, there is both a correlation with the clinical pathogenic mechanism, disseminated platelet aggregation, and with the therapeutic response to plasma infusion. Based upon our experience and the concept that thrombotic thrombocytopenic purpura is a plasma factor deficiency state, we recommend initial infusion of a full plasma volume equivalent over the first 24 hours. This should be done under an intensive care setting. After this initial plasma infusion, we advise the infusion of 3 units of plasma daily until a full remission is obtained. When the clinical situation has stabilized, we stop the daily plasma infusions and cautiously observe for recurrence of the manifestations of thrombotic thrombocytopenic purpura. If there is a recurrence, plasma is again infused in substantial quantity during the first 24 hours and then 3 units daily until a full remission is again evident. Whether the plasma requirement might be attenuated or the course of the disease shortened by the concomitant use of antiplatelet agents, corticosteroids or other means remains to be determined.