Platelet function analyzer (PFA)-100 closure time in the evaluation of platelet disorders and platelet function

Platelet function tests: a comparative review

In physiological hemostasis a prompt recruitment of platelets on the vessel damage prevents the bleeding by the rapid formation of a platelet plug. Qualitative and/or quantitative platelet defects promote bleeding, whereas the high residual reactivity of platelets in patients on antiplatelet therapies moves forward thromboembolic complications. The biochemical mechanisms of the different phases of platelet activation – adhesion, shape change, release reaction, and aggregation – have been well delineated, whereas their complete translation into laboratory assays has not been so fulfilled. Laboratory tests of platelet function, such as bleeding time, light transmission platelet aggregation, lumiaggregometry, impedance aggregometry on whole blood, and platelet activation investigated by flow cytometry, are traditionally utilized for diagnosing hemostatic disorders and managing patients with platelet and hemostatic defects, but their use is still limited to specialized laboratories. To date, a point-of-care testing (POCT) dedicated to platelet function, using pertinent devices much simpler to use, has now become available (ie, PFA-100, VerifyNow System, Multiplate Electrode Aggregometry [MEA]). POCT includes new methodologies which may be used in critical clinical settings and also in general laboratories because they are rapid and easy to use, employing whole blood without the necessity of sample processing. Actually, these different platelet methodologies for the evaluation of inherited and acquired bleeding disorders and/or for monitoring antiplatelet therapies are spreading and the study of platelet function is strengthening. In this review, well-tried and innovative platelet function tests and their methodological features and clinical applications are considered.

Assays of different aspects of haemostasis - what do they measure?

Haemostasis is a complex process affected by many factors including both cellular and plasma components. It is a multistep process starting with platelet adhesion to damaged endothelium and ending in clot fibrinolysis. There are several methods available to study different aspects of haemostasis including adhesion, aggregation, coagulation and fibrinolysis. This review describes the different methods, what aspects of haemostasis they measure and their limitations. Methods discussed include methods to study adhesion (e.g. PFA-100, cone and platelet(let) analyzer and perfusion chambers) and aggregation (e.g. Multiplate, VerifyNow and Plateletworks). Furthermore the principles behind viscoelastic haemostatic assays are presented as well as methods that can analyse aspects of haemostasis in plasma or platelet-rich-plasma samples (thrombin generation, overall haemostasis potential and Thrombodynamics Analyzer).

Absence of pharmacodynamic interaction between inclacumab and heparin in healthy smokers

Inclacumab is a novel monoclonal antibody directed against P-selectin in development for the prevention and treatment of atherosclerotic cardiovascular diseases. It is likely to be used concomitantly with heparin in patients undergoing percutaneous coronary intervention. Coadministration of both drugs may potentially increase the bleeding risk associated with heparin. This crossover study evaluated the potential pharmacodynamic interaction between inclacumab and unfractionated heparin in 18 healthy smokers. Owing to the long elimination of inclacumab (half-life of approximately 18 days), a 2-period, one-sequence study design was used. Subjects received an intravenous bolus injection of unfractionated heparin (5000 IU) on days 1 and 8 and an intravenous infusion of inclacumab (20 mg/kg) on day 8. Blood samples were collected on days 1 and 8 for pharmacodynamic effects of unfractionated heparin (anti-FXa and anti-FIIa activities, activated partial thromboplastin time and tissue factor pathway inhibitor) and over 6 months for pharmacokinetics of inclacumab. Sixteen subjects were eligible for pharmacodynamic analysis. Inclacumab had no clinically significant pharmacodynamic interaction with unfractionated heparin. With the exception of the minor but statistically significant increase of the maximum effect [Emax] of anti-FIIa activity, pharmacodynamic parameters (areas under the effect curve [AUElast] and Emax of anti-FXa) were almost similar on days 1 and 8. The 90% confidence intervals of geometric mean ratios of day 8 to day 1 for AUElast and Emax were however all contained within bioequivalence boundaries. The data demonstrate that the anticoagulant effect of unfractionated heparin was not affected by the administration of inclacumab.

Coagulation testing in the perioperative period

Perioperative coagulation management is a complex task that has a significant impact on the perioperative journey of patients. Anaesthesia providers play a critical role in the decision-making on transfusion and/or haemostatic therapy in the surgical setting. Various tests are available in identifying coagulation abnormalities in the perioperative period. While the rapidly available bedside haemoglobin measurements can guide the transfusion of red blood cells, blood product administration is guided by many in vivo and in vitro tests. The introduction of newer anticoagulant medications and the implementation of the modified in vivo coagulation cascade have given a new dimension to the field of perioperative transfusion medicine. A proper understanding of the application and interpretation of the coagulation tests is vital for a good perioperative outcome.

Hermansky-Pudlak syndrome. Overview of clinical and molecular features and case report of a new HPS-1 variant

Hermansky-Pudlak syndrome (HPS) is a rare, autosomal recessive disorder affecting lysosome-related organelles (LRO), including dense platelet granules. HPS causes oculocutaneous hypopigmentation, bleeding diathesis and granulomatous colitis or pulmonary fibrosis. To date, there is no curative treatment and the clinical management depends on the severity of symptoms. A prompt diagnosis of HPS patients could improve their quality of life and clinical management. However, the absence of a specific platelet function test, the wide molecular heterogeneity, and the lack of phenotype-genotype correlations hamper the rapid diagnosis. Nine subtypes of HPS have been identified as a result of mutations in nine genes that codify for proteins involved in formation and shuttle of the LRO. The molecular characterization of patients and knowledge derived from animal models of HPS contribute to the understanding of biogenesis and function of the LRO. This paper describes a patient with a novel homozygous nonsense mutation causing HPS and provides a review of the literature focusing on recent advances in the molecular characterization and physiopathology of HPS.

Assessment of platelet function: Laboratory and point-of-care methods

In the event of blood vessel damage, human platelets are promptly recruited on the site of injury and, after their adhesion, activation and aggregation, prevent blood loss with the formation of a clot. The consequence of abnormal regulation can be either hemorrhage or the development of thrombosis. Qualitative and/or quantitative defects in platelets promote bleeding, whereas the residual reactivity of platelets, despite antiplatelet therapies, play an important role in promoting arterial thrombotic complications. Platelet function is traditionally assessed to investigate the origin of a bleeding syndrome, to predict the risk of bleeding prior surgery or during pregnancy or to monitor the efficacy of antiplatelet therapy in thrombotic syndromes that, now, can be considered a new discipline. “Old” platelet function laboratory tests such as the evaluation of bleeding time and the platelet aggregation analysis in platelet-rich plasma are traditionally utilized to aid in the diagnosis and management of patients with platelet and hemostatic disorders and used as diagnostic tools both in bleeding and thrombotic diathesis in specialized laboratories. Now, new and renewed automated systems have been introduced to provide a simple, rapid assessment of platelet function including point of care methods. These new methodologies are also suitable for being used in non-specialized laboratories and in critical area for assessing platelet function in whole blood without the requirement of sample processing. Some of these methods are also beginning to be incorporated into routine clinical use and can be utilized as not only as first panel for the diagnosis of platelet dysfunction, but also for monitoring anti-platelet therapy and to potentially assess risk of both bleeding and/or thrombosis.

The effect of hetastarch 670/0.75 administered in vivo as a constant rate infusion on platelet closure time in the dog

OBJECTIVE

To evaluate the effects of hetastarch 670/0.75 on canine platelet function and clinical bleeding following its administration as a constant rate infusion (CRI) at 1 mL/kg/h and 2 mL/kg/h for 24 hours.

DESIGN

In vivo, prospective, open-label, crossover study.

SETTING

Research laboratory at a university veterinary facility.

ANIMALS

Eight healthy, adult male research dogs.

INTERVENTIONS

Each dog received 1 mL/kg/h hetastarch for 24 hours then 2 mL/kg/h with a washout period of 10 weeks between each experiment. Platelet closure time (CT) was measured using a platelet function analyzer with collagen adenosine diphosphate (ADP) cartridges. CT measurements were performed at baseline and 6, 12, and 24 hours following initiation of hetastarch infusion.

MEASUREMENTS AND MAIN RESULTS

At 1 mL/kg/h, mean CT was significantly increased at the 12- and 24-hour time point relative to the baseline value, although mean CT never rose to a value above the reference interval during the 24-hour infusion. At 2 mL/kg/h, median CT was also significantly increased at the 12- and 24-hour time point relative to the baseline value. Administration of 2 mL/kg/h did progressively prolong the median CT value though only exceeded the reference interval at the 24-hour time point. Despite the prolongation of median CT, there was no clinical evidence of spontaneous bleeding in any dog during the 24-hour infusion at either CRI rate.

CONCLUSIONS

Hetastarch 670/0.75 when used as a 24-hour CRI at 1 and 2 mL/kg/h prolongs CT in healthy dogs at 6, 12, and 24 hours. Median CT only exceeded the reference interval at 24 hours at 2 mL/kg/h.

Inconsistency of different methods for assessing ex vivo platelet function: relevance for the detection of aspirin resistance

BACKGROUND

Assays to evaluate platelet function are often interchangeably used to assess "resistance" to aspirin. We compared different platelet function assays in patients treated or untreated with aspirin.

DESIGN AND METHODS

Platelet function was evaluated in 162 subjects, 85 of whom were not being treated with any antiplatelet drug and 77 of whom were receiving chronic therapy with low-dose aspirin. Platelet Function Analyzer collagen/ADP- and collagen/epinephrine closure times, as well as light transmittance aggregometry in response to ADP, collagen and arachidonic acid (this last in 47 aspirin-treated patients) were determined. In 43 aspirin-treated patients, serum thromboxane B(2) levels were also measured.

RESULTS

In untreated patients, collagen/ADP- and collagen/epinephrine-closure times were correlated with each other (r=0.5, P=0.0001), but did not correlate with ADP- or collagen-induced aggregation. In patients treated with aspirin, collagen/ADP-closure time values were not different from those in untreated patients, while the collagen/epinephrine-closure time was prolonged. ADP-induced aggregation was unaffected by aspirin, while collagen-induced aggregation was reduced. Arachidonic acid-induced aggregation was almost completely suppressed (% maximum light transmittance aggregometry =5 ± 13%). There was, however, no correlation between the various platelet function tests. Serum thromboxane B(2), an index of platelet cyclooxygenase-1 activity, was almost completely suppressed (down to 8 ± 17 ng/mL) in treated patients, and was not correlated with arachidonic acid-, ADP- and collagen-induced aggregation or with collagen/ADP-closure time, but was inversely correlated with collagen/epinephrine-closure time.

CONCLUSIONS

There is a high heterogeneity of results of tests evaluating inhibition of platelet function by aspirin, and the results of functional tests do not match biochemical measurement of cyclooxygenase-1 activity. Extreme caution should, therefore, be used in defining "resistance" to aspirin on the basis of the results of these tests.

Platelet function tests: a review of progresses in clinical application

The major goal of traditional platelet function tests has been to screen and diagnose patients who present with bleeding problems. However, as the central role of platelets implicated in the etiology of arterial thrombotic diseases such as myocardial infarction and stroke became widely known, platelet function tests are now being promoted to monitor the efficacy of antiplatelet drugs and also to potentially identify patients at increased risk of thrombosis. Beyond hemostasis and thrombosis, an increasing number of studies indicate that platelets play an integral role in intercellular communication, are mediators of inflammation, and have immunomodulatory activity. As new potential biomarkers and technologies arrive at the horizon, platelet functions testing appears to take on a new aspect. This review article discusses currently available clinical application of platelet function tests, placing emphasis on essential characteristics.

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.

Assessment methods for aspirin-mediated platelet antiaggregation in type 2 diabetic patients: degree of correlation between 2 point-of-care methods

AIMS

Impaired response to antiplatelet therapy in diabetic patients results in a higher incidence of drug-eluting stent thrombosis. This study determined the prevalence of high on-aspirin (AS) platelet reactivity in type 2 diabetic patients treated with percutaneous coronary intervention (PCI) using the VerifyNow Aspirin Assay (VN) and platelet function analyzer PFA-100 (PFA-100) and analyzed the correlation between both methods.

METHODS

Type 2 diabetic patients (100) with non-ST-elevation acute coronary syndrome who underwent PCI and Xience V drug-eluting stent implantation were included in this study. After PCI, platelet antiaggregation mediated by acetylsalicylic acid was assessed by VN and PFA-100. The degree of correlation and concordance was then determined.

RESULTS

When assayed with VN, 7% of the patients were nonresponders to aspirin (aspirin reaction units >550), and when assayed with PFA-10, 41% were nonresponders (closure time <193 seconds). Of the patients, 4% were nonresponders to aspirin according to VN but were sensitive to aspirin according to PFA-100, and 38% were sensitive to aspirin according to VN and nonresponders according to PFA-100. Overall, 55% of the patients were aspirin-sensitive in both methods. The Spearman's coefficient between VN and PFA-100 results was r = 0.09 (P = 0.35). The kappa index value was 0.0062 (P = 0.91).

CONCLUSIONS

There is no concordance or correlation between the VN and PFA-100 results. Therefore, the use of these analyses should be restricted to clinical research, which limits its application in clinical practice.

Laboratory investigation of platelet function in patients with thalassaemia

The aim of this study was to investigate platelet function in patients with thalassaemia and to detect any relation to chelation treatment (deferasirox or deferiprone/deferiprone plus desferioxamine). Thirty-three transfusion-dependent patients with thalassaemia were included. The investigation consisted of aggregation testing of platelet-rich plasma by light transmission aggregometry (LTA) with the use of 5 agonists as well as the global test of haemostasis by means of the PFA-100 platelet function analyser. In 66.67% of the patients, there was reduced LTA to at least one agonist and in 18.18% there was reduced LTA to two or more agonists. The PFA-100 test was prolonged in 60.6% of the cases. An abnormal LTA and a prolonged PFA-100 time were recorded in 33.3% of the patients and 27.4% had a normal aggregation and PFA-100 test. No correlation between chelation regimen and either LTA or PFA-100 test was found. The abnormal LTA can be explained either by the release of ADP from the haemolysed red blood cells, which leads to defective platelet aggregation, or by the presence of two platelet populations. An in vitro effect without an in vivo impact could be an alternative explanation. In patients with thalassaemia, the reduced LTA and the prolonged PFA-100 closure time could be an in vitro effect and has a close correlation to the bleeding phenotype of each patient.

Platelet function testing: state of the art

Platelet function testing has evolved from crude tests, such as the bleeding time, to tests that permit a relatively sophisticated evaluation of platelet activity. Nonetheless, these tests are hampered by lack of specificity and sensitivity, and poor standardization of methods and techniques. The bleeding time, which has long been a staple of hemostasis testing, has been dropped from the test menu at many laboratories. In its place, tests such as the Platelet Function Analyzer-100 are increasingly used to screen patients with possible bleeding disorders. Older tests, such as platelet aggregometry and lumiaggregometry, are still used frequently because they provide insight into receptor, signaling pathway and granule release mechanisms. Flow cytometry is available in some specialized laboratories and allows for quantitative and qualitative assessment of some platelet functions, although the expense of testing is often prohibitive. Finally, the wider availability of platelet function testing has stimulated interest and demand for monitoring the effect of platelet inhibitory drugs, such as aspirin and clopidogrel. As platelet function pathways become better understood, the demand for these type of monitoring tests is likely to increase.

Testing platelet function

Platelet function tests have been traditionally used to aid in the diagnosis and management of patients with bleeding problems. Given the role of platelets in atherothrombosis, several dedicated platelet function instruments are now available that are simple to use and can be used as point-of-care assays. These can provide rapid assessment of platelet function within whole blood without the requirement of sample processing. Some tests can be used to monitor antiplatelet therapy and assess risk of bleeding and thrombosis, although current guidelines advise against this. This article discusses the potential utility of tests/instruments that are available.

Inherited platelet function disorders: overview and disorders of granules, secretion, and signal transduction

Inherited disorders of platelet function are characterized by highly variable mucocutaneous bleeding manifestations. The platelet dysfunction arises by diverse mechanisms, including abnormalities in platelet membrane glycoproteins, granules and their contents, platelet signaling and secretion mechanisms: thromboxane production pathways and in platelet procoagulant activities. Platelet aggregation and secretion studies using platelet-rich plasma currently form the primary basis for the diagnosis of an inherited platelet dysfunction. In most such patients, the molecular and genetic mechanisms are unknown. Management of these patients needs to be individualized; therapeutic options include platelet transfusions, 1-desamino-8d-arginine vasopressin (DDAVP), recombinant factor VIIa, and antifibrinolytic agents.

Congenital thrombocytopenia: clinical manifestations, laboratory abnormalities, and molecular defects of a heterogeneous group of conditions

Once considered exceptionally rare, congenital thrombocytopenias are increasingly recognized as a heterogeneous group of disorders characterized by a reduction in platelet number and a bleeding tendency that may range from very mild to life threatening. Although some of these disorders affect only megakaryocytes and platelets, others involve different cell types and may result in characteristic phenotypic abnormalities. This review elaborates the clinical presentation and laboratory manifestations of common congenital thrombocytopenias in addition to exploring our understanding of the molecular basis of these disorders and therapeutic interventions available.

Inherited disorders of platelet function

Inherited platelet function disorders are of variable severity and unknown frequency and may be difficult to diagnose. Nevertheless, they are increasingly recognized as an important cause of bleeding in pediatrics, particularly in adolescent girls with menorrhagia, where they may be more common than von Willebrand disease. This article reviews the presentation of these disorders, summarizes the most common types of platelet function disorders, discusses the challenges in diagnostic testing, and details treatment and supportive care options.

Usefulness of the INNOVANCE PFA P2Y test cartridge for the detection of patients with congenital defects of the platelet P2Y₁₂ receptor for adenosine diphosphate

INTRODUCTION

The platelet function analyzer (PFA)-100 is used in clinical practice to screen patients with bleeding diathesis and suspected defects of primary hemostasis. A new cartridge, INNOVANCE PFA P2Y, has been specifically developed to monitor patients' response to drugs inhibiting the platelet P2Y₁₂ receptor for ADP. In this study, we compared the ability of INNOVANCE PFA P2Y to detect congenital defects of the platelet P2Y₁₂ receptor to that of standard cartridge formulations currently in clinical use.

MATERIALS AND METHODS

We studied two patients with severe P2Y₁₂ deficiency, one patient with heterozygous P2Y₁₂ deficiency and one with dysfunctional P2Y₁₂ receptor. Closure times were measured using 3 cartridges: collagen/ADP, collagen/epinephrine, and INNOVANCE PFA P2Y. The results obtained in the four patients with P2Y₁₂ defects were compared to those obtained for 20 healthy controls.

RESULTS

In 2 patients with severe P2Y₁₂ deficiency, closure times of INNOVANCE PFA P2Y and collagen/ADP cartridges were >300 s, while those of collagen/epinephrine cartridge were variable (186s and >300 s). In the patient with dysfunctional P2Y₁₂, closure time of INNOVANCE PFA P2Y was >300 s, while closure times of collagen/ADP and collagen/epinephrine were normal. Closure times of all cartridges were normal in the patient with heterozygous P2Y₁₂ deficiency.

CONCLUSION

Our study provides the first evidence that INNOVANCE PFA P2Y cartridge is sensitive to congenital severe and moderate defects of the platelet P2Y₁₂ receptors.

Aspirin resistance: a clinical review focused on the most common cause, noncompliance

Aspirin is an inexpensive, readily available medication that reduces the risk of subsequent vascular disease by about 25% in patients with known occlusive vascular disease. Aspirin's beneficial effect is mediated via inhibition of arachidonic acid (AA) activation of platelets and is detected by demonstrating a decrease in platelet function and/or a decrease in prostaglandin metabolites. Patients who are assumed to be taking their aspirin, but who do not demonstrate an aspirin effect are labeled as, "aspirin resistant." This is an unfortunate designation as the vast majority of patients labeled as "aspirin resistant" are noncompliant. Noncompliance is demonstrated in multiple studies that use repeat testing for platelet inhibition in patients with an initial inadequate response to aspirin. When the test is repeated under condition where ingestion of the test aspirin is assured, the patients' platelets are inhibited. Instead of using the term "aspirin resistance," this review will use "inadequate response to aspirin." Patients with an inadequate aspirin response have an increased likelihood for subsequent vascular events. Detection and treatment of an inadequate aspirin response would be facilitated by the development of a bedside assay that uses whole blood, is technically simple, inexpensive, sensitive, specific, reproducible, and provides an answer in a few minutes. Future research in patients with an inadequate response to aspirin should focus on mechanisms to improve compliance, which should decrease their risk of future vascular events.

Therapy with acetylsalicylic acid does not interfere with oral surgery

The acetylsalicylic acid (ASA) treatment is widespread therapeutic strategy in cardiology clinics. On the other hand, patients with heart diseases represent a significant group of cases in dental clinics. Accordingly, we studied the local hemostatic thrombus formation after dental tooth extractions (n=47) and other oral surgery treatment (n=13) in 60 patients with heart disease being on ASA therapy without drug discontinuation. In the control group free of ASA therapy it was: (n=24) and (n=6), respectively. In all studied patients, the aggregative activity of blood platelets by PFA-100 analyzer was assessed. It was found that 61.7% patients treated with ASA presented inhibition of platelets aggregation. Unexpectedly, in 35% of such patients, platelet aggregation function remained unchanged. In the control group, normal platelet aggregation was found in all subjects. It has been shown that ASA therapy has neutral effects on both thrombus formation and pain complications in patients with heart disease underwent tooth extraction and other oral surgery. Thus discontinuation of ASA therapy before surgery seems to be weakly validated.

Advances in our understanding of "resistance" to antiplatelet agents for prevention of ischemic stroke

We review the role of aspirin and clopidogrel for prevention of ischemic stroke and explore the concept of antiplatelet therapy resistance both from a laboratory and clinical perspective and genetic polymorphisms that might influence platelet reactivity with clopidogrel administration. Debates have raged over the years about the application of platelet function tests in clinical practice. We conclude that platelet function testing is not indicated in routine clinical practice. This recommendation is supported by clinical guideline statements, a lack of a global platelet function measure, and limitations of current platelet function test methods as applied in practice. We discuss a recently hypothesized hierarchy of patient characteristics in relation to which patients are most likely to benefit from platelet function studies based on acuity (i.e., risk) of cardiovascular disease. A focus of antiplatelet therapy administration should include emphasis on compliance/adherence and in the example of aspirin, use of well-absorbed forms of aspirin and avoidance of drugs that may interact with aspirin to inhibit its mechanism of action (e.g., certain nonsteroidal anti-inflammatory drugs).

Human albumin in extracorporeal prime: effect on platelet function and bleeding

Purpose:

Synthetic starches have been positioned as an equivalent substitute for human albumin in extracorporeal prime, with both providing osmotic and oncotic pressure. Another effect of albumin is its ability to coat the synthetic surfaces of an extracorporeal circuit with a biopassivating protein monolayer. Whether this protein biopassivation has any benefit to the patient, assessed by platelet count, platelet function and 24-hour bleeding rate, is considered.

Methods:

Patients presenting for coronary artery bypass at a Canadian tertiary care hospital were randomized into two groups until a final study size of 20 patients was obtained. The Study Group received 2.5 g of human albumin in the extracorporeal prime and the Control Group remained protein free. Both groups included Voluven 6% as a synthetic starch. Blood samples were obtained at three intervals; Pre-bypass, During bypass (30 minutes after initiation of bypass), and Post-bypass. These samples were assayed for platelet function, platelet count and hemoglobin. Chest tube drainage over a 24-hour period was monitored.

Results:

Platelet count was significantly higher in the During sample in the Study Group (196 ± 56.5 x 109/ml versus 160 ± 18.5 x 109/ml, p<0.05), however, this difference was no longer significant with the Post-bypass sample (135 ±36.0 x 109/mL versus 127 ±19 x 109/mL). Platelet function assays (PFA) showed no significant differences. Chest tube drainage after 24 hours was significantly lower in the Study Group (586 ± 131.8 ml/24 h versus 741 ± 272.5 ml/24 h, p<0.05).

Conclusions:

Human albumin can passivate the synthetic surfaces of the extracorporeal circuit, which is supported by observations of preserved platelet count and reduced chest tube drainage. Although some statistically significant benefits were observed, the practical benefits of passivating an extracorporeal circuit with human albumin may be minimal.

Microfluidics and coagulation biology

The study of blood ex vivo can occur in closed or open systems, with or without flow. Microfluidic devices, which constrain fluids to a small (typically submillimeter) scale, facilitate analysis of platelet function, coagulation biology, cellular biorheology, adhesion dynamics, and pharmacology and, as a result, can be an invaluable tool for clinical diagnostics. An experimental session can accommodate hundreds to thousands of unique clotting, or thrombotic, events. Using microfluidics, thrombotic events can be studied on defined surfaces of biopolymers, matrix proteins, and tissue factor, under constant flow rate or constant pressure drop conditions. Distinct shear rates can be generated on a device using a single perfusion pump. Microfluidics facilitated both the determination of intraluminal thrombus permeability and the discovery that platelet contractility can be activated by a sudden decrease in flow. Microfluidic devices are ideal for multicolor imaging of platelets, fibrin, and phosphatidylserine and provide a human blood analog to mouse injury models. Overall, microfluidic advances offer many opportunities for research, drug testing under relevant hemodynamic conditions, and clinical diagnostics.

Clinical and laboratory characteristics of adolescents with platelet function disorders and heavy menstrual bleeding

BACKGROUND

Platelet function disorders (PFDs) have emerged as an important etiology of heavy menstrual bleeding (HMB) in adolescents. However, neither clinical nor laboratory data have been methodically analyzed in this population subset. The objective of this study was to evaluate these parameters in order to distinguish characteristics of the disorder that in turn will lead to earlier diagnosis and therapy initiation.

METHODS

Retrospective review of medical records from postmenarcheal adolescents with documented PFDs referred to a hemophilia treatment center and university faculty practices for bleeding diatheses with their clinical and laboratory data evaluated.

RESULTS

Of 63 teens with documented PFDs, HMB was the most common clinical manifestation of PFD (43; 68.3%). Of these, 37 (86%) were diagnosed with PFD either at or after menarche with the diagnosis based on HMB symptoms alone. Only 6 (14%) were diagnosed with a PFD prior to menarche, based on associated bleeding, i.e., epistaxis, ecchymosis, and all developed HMB after menstruation onset. Interestingly, 20 girls were diagnosed with a PFD prior to menarche and of these, only 6 (30%) went on to develop HMB after pubertal transition, while the majority (14; 70%) did not. The average age-at-PFD diagnosis was 14.5yrs, significantly differing from the 10.9yrs average age-at-PFD diagnosis in their counterparts that, after menarche, did not develop HMB (P<.01) Blood type O occurred significantly more frequently (76%) than national norms (P <.037). Incidence of δ-Storage Pool deficiency (δ-SPD) was significantly higher (74%) than their non-HMB cohorts (45%) (P <.007). Coagulation and von Willebrand factor studies were all normal. Abnormal closure times and aggregation studies were observed in 42% and 60%, respectively, of tested girls. In 25.6% for whom standard platelet studies were normal, electron microscopy detected reduced platelet δ-granules numbers (δ-SPD).

CONCLUSIONS

Adolescents with PFDs and HMB appear to be clinically distinct from their non-HMB counterparts. This group of girls is characterized by HMB the major bleeding symptom, significantly high incidences of blood group O and the δ-SPD with a PFD diagnosed well after menarche. High false negative standard platelet function study results indicate additional diagnostic strategies, particularly for δ-SPD, should be considered.

Time-dependent changes in non-COX-1-dependent platelet function with daily aspirin therapy

To develop an integrated metric of non-COX-1-dependent platelet function (NCDPF) to measure the temporal response to aspirin in healthy volunteers and diabetics. NCDPF on aspirin demonstrates wide variability, despite suppression of COX-1. Although a variety of NCDPF assays are available, no standard exists and their reproducibility is not established. We administered 325 mg/day aspirin to two cohorts of volunteers (HV1, n = 52, and HV2, n = 96) and diabetics (DM, n = 74) and measured NCDPF using epinephrine, collagen, and ADP aggregometry and PFA100 (collagen/epi) before (Pre), after one dose (Post), and after several weeks (Final). COX-1 activity was assessed with arachidonic acid aggregometry (AAA). The primary outcome of the study, the platelet function score (PFS), was derived from a principal components analysis of NCDPF measures. The PFS strongly correlated with each measure of NCDPF in each cohort. After 2 or 4 weeks of daily aspirin the Final PFS strongly correlated (r > 0.7, P < 0.0001) and was higher (P < 0.01) than the Post PFS. The magnitude and direction of the change in PFS (Final–Post) in an individual subject was moderately inversely proportional to the Post PFS in HV1 (r = -0.45), HV2 (r = -0.54), DM (r = -0.68), P < 0.0001 for all. AAA remained suppressed during aspirin therapy. The PFS summarizes multiple measures of NCDPF. Despite suppression of COX-1 activity, NCDPF during aspirin therapy is predictably dynamic: those with heightened NCDPF continue to decline whereas those with low/normal NCDPF return to pre-aspirin levels over time.

Platelet function in health and disease: from molecular mechanisms, redox considerations to novel therapeutic opportunities

Increased oxidative stress appears to be of fundamental importance in the pathogenesis and development of several disease processes. Indeed, it is well known that reactive oxygen species (ROS) exert critical regulatory functions within the vascular wall, and it is, therefore, plausible that platelets represent a relevant target for their action. Platelet activation cascade (including receptor-mediated tethering to the endothelium, rolling, firm adhesion, aggregation, and thrombus formation) is tightly regulated. In addition to already well-defined platelet regulatory factors, ROS may participate in the regulation of platelet activation. It is already established that enhanced ROS release from the vascular wall can indirectly affect platelet activity by scavenging nitric oxide (NO), thereby decreasing the antiplatelet properties of endothelium. On the other hand, recent data suggest that platelets themselves generate ROS, which may evoke pro-thrombotic responses, triggering many biological processes participating in atherosclerosis initiation, progression, and complication. That oxidative stress may alter platelet function is conceivable when considering that antioxidants play a role in the prevention of cardiovascular disease, although the precise mechanism accounting for changes attributable to antioxidants in atherosclerosis remains unknown. It is possible that the effects of antioxidants may be a consequence of their enhancing or promoting the antiplatelet effects of NO derived from both endothelial cells and platelets. This review focuses on current knowledge regarding ROS-dependent regulation of platelet function in health and disease, and summarizes in vitro and in vivo evidence for their physiological and potential therapeutic relevance.

Global haemostasis and point of care testing

The evaluation of the coagulation profile has used so far either clotting-based or chromogenic assays with different endpoints. Clotting-based techniques are the most used worldwide, and they certainly are useful for diagnosis of clotting factor deficiencies. However, the information provided is relatively limited, and therefore the individual profile of coagulation is poorly assessed. This is reflected by the weak correlation between the results of these assays and the clinical phenotype. Among the assays that benefited from technological advances, thrombin generation and thromboelastography are probably the most actively investigated, but they require specific instruments and are not fully automated. Their standardisation level is rapidly progressing, and they are progressively entering the clinical scene, with the attempt to provide additional information on the coagulation process and a meaningful clinical correlation. These inherited bleeding disorders frequently require replacement therapy using clotting factor concentrates that increase the plasma level of the missing clotting factor. The classical adjustment of the therapy is mainly based on the measurement of the plasma clotting activity of the protein administered. If one considers that a certain level of thrombin generated would predict clinical efficacy, monitoring of thrombin formation might offer new possibilities to individually predict the bleeding phenotype, select the most adapted therapeutic product and tailor the dose. The same holds true for thromboelastography/thromboelastometry which evaluate fibrin formation as well as clot resistance to fibrinolytic challenge, one step further down in the coagulation process. In this regard, these 2 assays could be seen as complementary in terms of information provided on the coagulation profile at the individual level.

Platelet response to aspirin in Chinese stroke patients is independent of genetic polymorphisms of COX-1 C50T and COX-2 G765C

AIM

Aspirin resistance (AR) is common in Chinese stroke patients taking antiplatelet medications; however, few studies have documented the role of cyclooxygenase (COX)-1 C50T and COX-2 G765C polymorphisms in AR. The aim of this study was to investigate the prevalence of AR in Chinese stroke patients and the relationships between AR and COX-1 C50T and COX-2 G765C polymorphisms, and to evaluate the effect of these polymorphisms on platelet response to aspirin.

METHODS

We prospectively enrolled 634 Chinese stroke patients. Platelet aggregation testing was performed before and after aspirin administration. The pre- and post-aspirin levels of 11-dehydrothromboxane B(2) (11-dTxB(2)) were determined in urine samples. COX-1 C50T and COX-2 G765C genotypes were determined by a polymerase chain reaction-allelic restriction assay.

RESULTS

AR was detected in 129 patients (20.4%), aspirin semi-resistance (ASR) was detected in 28 patients (4.4%), and aspirin sensitivity (AS) was detected in 477 patients (75.2%). There was no association between COX-1 C50T or COX-2 G765C polymorphisms and ASR+AR. Aspirin could efficiently reduce 11-dTxB(2) production by approximately 75%. In addition, platelet aggregation, both in response to arachidonic acid (AA) and adenosine 5'-diphosphate (ADP), was inhibited by more than 80% and 40%, respectively; however, the percentage reduction in platelet aggregation and 11-dTxB(2) levels was not significantly different between the COX-1 C50T and COX-2 G765C genotypes (p＞0.05).

CONCLUSIONS

There was no association between COX-1 C50T and COX-2 G765C polymorphisms and AR in Chinese stroke patients. In addition, COX-1 C50T and COX-2 G765C polymorphisms had no effect on the platelet response to aspirin.

Approaches to investigating common bleeding disorders: an evaluation of North American coagulation laboratory practices

Bleeding disorders commonly result from deficiencies or defects in von Willebrand factor (VWF), platelets, coagulation factors, or fibrinolytic proteins. The primary goal of our study was to assess current North American coagulation laboratory practices for diagnosing bleeding disorders, using an on-line patterns-of-practice survey of diagnostic laboratory members of the North American Specialized Coagulation Laboratory Association. The survey examined laboratory approaches to evaluating bleeding disorders, with specific questions about the tests and test panels offered and compliance to recent guideline recommendations on diagnosing von Willebrand disease (VWD) and platelet function disorders. All laboratories responding to the survey performed a prothrombin time/international normalized ratio, an activated partial thromboplastin time, and coagulation factor assays, and many tested for VWD and platelet disorders. However, few laboratories had test panels that evaluated the more common bleeding disorders and few performed some assays, including VWF multimer assessments and assays for fibrinolytic disorders. Additionally, the cutoffs used by laboratories to diagnose type 1 VWD varied considerably, with only a minority following the National Heart Lung Blood Institute recommendations. In contrast, laboratories that tested for platelet function disorders mostly complied with aggregation testing recommendations, as published in the recent North American guidelines. Our results indicate that there are some gaps in the strategies used by laboratories to diagnose bleeding disorders that might be addressed by development of further guidelines and test algorithms that emphasize evaluations for common bleeding disorders. Laboratories may also benefit from guidelines on test interpretation, and external evaluation of their bleeding disorder testing strategies.

Evaluation of hemostasis in flowing blood

Hemostasis and thrombosis are now increasingly recognized as integrally related to blood rheology and blood flow. Platelets, for example, are known to access the vessel wall in ways which depend upon the small-scale motions of neighboring erythrocytes, and access one another via collisions driven by gradients in blood flow velocity. In this context, flow devices have become a subject of great interest in the clinical assessment of bleeding disorders, especially platelet function defects and von Willebrand disease. While these devices currently lack standardization and outcomes measures which establish clear clinical utility, their promise remains great, particularly in the potential to simulate the microenvironment of arteries vs. veins and in their ability to incorporate such intrinsically flow-dependent phenomena as co-localization of tissue-factor-bearing microparticles with platelets, the weakness of the GPIb-vWF bond at very high shear stresses, and even the hemostatic and antithrombotic function of vascular endothelium. In contrast, currently utilized assays are often performed under static conditions that do not involve flow and therefore are not able to simulate the microenvironment of arteries and veins.

Assessment of a cohort of primarily pediatric patients with a presumptive diagnosis of type 1 von Willebrand disease with a novel high shear rate, non-citrated blood flow device

BACKGROUND

A precise approach to the diagnosis of von Willebrand disease (vWD) remains elusive. One important reason is that vWD is a blood flow-related disorder: a vW Factor-platelet GPIb binding defect exists in this condition under the high shear-rate (> 1000 sec-1 in whole blood; > 3000 sec-1 in PRP) conditions of physiologic blood flow which exist in the arterioles of mucous membranes, from which most bleeding in vWD occurs.

METHODS

We therefore studied 28 patients (mean 18.9 yrs) with vWD, diagnosed according to the 2007 NHLBI clinical guidelines, and 26 healthy controls (mean 17.5 yrs). Blood was collected into a plastic tube containing 4 U/ml FC dalteparin, 1.75 μg/ml of the Tab (anti-CD41) monoclonal antibody directed against platelet GPIIb, and 1.0 μg/ml of an ALEXA 555-conjugated rabbit anti-mouse second antibody. Within 30-90 min, the blood was then withdrawn at 667 and 1330 sec(-1) through a special flow chamber allowing for real-time epifluorescence digital videomicroscopy of platelets interacting with a microfibrillar collagen substrate. With MetaMorph software (Universal Imaging) we quantified the percent area (PA) covered by and total volume (TV) of adherent platelet aggregates within a 435 μm × 580 μm field of view.

RESULTS

At 667 sec(-1) after 1 min PA and TV were similar for patients and controls, but at 1330 sec(-1) PA was 9.32 ± 4.21 (mean ± SD) for patients, a value lower (p < 0.001) than the 12.8 ± 3.39 for controls. TV was (1.43 ± 0.91) x 10(4) for patients, a value also lower (p < 0.001) than the (2.22 ± 0.77) x 10(4) for controls. PA or TV was below the 2.5th percentile for controls in 10 patients (36%) and both PA and TV were below the 2.5th percentile in eight.

CONCLUSIONS

The novel flow device found that PA and TV were significantly reduced under high shear stress in vWD patients compared to normal controls. However, there was some overlap between the vWD and the control group, suggesting that some vWD patients had normal platelet adhesion/aggregation under the conditions studied. Further study with a higher shear rate appears indicated.