PFA-100 system: a new method for assessment of platelet dysfunction

Utility of Global Hemostatic Assays in Patients with Bleeding Disorders of Unknown Cause

Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion after exhaustive evaluation of plasmatic coagulation and platelet function. This review explores the utility of global hemostatic assays as confirmatory tests and in elucidating the pathophysiology of BDUC. Unlike traditional hemostatic tests that focus on coagulation factors, global assays are conducted both in plasma and also whole blood. These assays provide a more comprehensive understanding of the cell-based model of coagulation, aid in the identification of plasmatic factor abnormalities that may reduce hemostatic capacity, and allow for the assessment of impaired platelet-endothelial interactions under shear stress, as well as hyperfibrinolytic states. While clinical tests such as skin bleeding time and global assays such as PFA-100 exhibit limited diagnostic capacity, the role of viscoelastic testing in identifying hemostatic dysfunction in patients with BDUC remains unclear. Thrombin generation assays have shown variable results in BDUC patients; some studies demonstrate differences compared with healthy controls or reference values, whereas others question its clinical utility. Fibrinolysis assessment in vitro remains challenging, with studies employing euglobulin clot lysis time, plasma clot lysis time, and fluorogenic plasmin generation yielding inconclusive or conflicting results. Notably, recent studies suggest that microfluidic analysis unveils shear-dependent platelet function defects in BDUC patients, undetected by conventional platelet function assays. Overall, global assays might be helpful for exploring underlying hemostatic impairments, when conventional hemostatic laboratory tests yield no results. However, due to limited data and/or discrepant results, further research is needed to evaluate the utility of global assays as screening tools.

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.

Evolution of Hemostasis Testing: A Personal Reflection Covering over 40 Years of History

There is no certainty in change, other than change is certain. As Seminars in Thrombosis and Hemostasis celebrates 50 years of publication, I felt it appropriate to reflect on my own 40-year plus scientific career. My career in the thrombosis and hemostasis field did not start until 1987, but the subsequent 35 years reflected a period of significant change in associated disease diagnostics. I started in the Westmead Hospital "coagulation laboratory" when staff were still performing manual clotting tests, using stopwatches, pipettes, test tubes, and a water bath, which we transported to the hospital outpatient department to run our weekly warfarin clinic. Several hemostasis instruments have come and gone, including the Coag-A-Mate X2, the ACL-300R, the MDA-180, the BCS XP, and several StaR Evolution analyzers. Some instruments remain, including the PFA-100, PFA-200, the AggRAM, the CS-5100, an AcuStar, a Hydrasys gel system, and two ACL-TOP 750s. We still have a water bath, but this is primarily used to defrost frozen samples, and manual clotting tests are only used to teach visiting medical students. We have migrated across several methodologies in the 45-year history of the local laboratory. Laurel gel rockets, used for several assays in the 1980s, were replaced with enzyme-linked immunosorbent assay assays and most assays were eventually placed on automated instruments. Radio-isotopic assays, used in the 1980s, were replaced by an alternate safer method or else abandoned. Test numbers have increased markedly over time. The approximately 31,000 hemostasis assays performed at the Westmead-based laboratory in 1983 had become approximately 200,000 in 2022, a sixfold increase. Some 90,000 prothrombin times and activated partial thromboplastic times are now performed at this laboratory per year. Thrombophilia assays were added to the test repertoires over time, as were the tests to measure several anticoagulant drugs, most recently the direct oral anticoagulants. I hope my personal history, reflecting on the changes in hemostasis testing over my career to date in the field, is found to be of interest to the readership, and I hope they forgive any inaccuracies I have introduced in this reflection of the past.

International Council for Standardization in Haematology Guidance for New Lot Verification of Coagulation Reagents, Calibrators, and Controls

The clinical laboratory uses commercial products with limited shelf life or certain expiry dates requiring frequent lot changes. Prior to implementation for clinical use, laboratories should determine the performance of the new reagent lot to ensure that there is no significant shift in reagent performance or reporting of patient data. This guideline has been written on behalf of the International Council for Standardization in Haematology (ICSH) to provide the framework and provisional guidance for clinical laboratories for evaluating and verifying the performance of new lot reagents used for coagulation testing. These ICSH Working Party consensus recommendations are based on good laboratory practice, regulatory recommendations, evidence emerged from scientific publications, and expert opinion and are meant to supplement regional standards, regulations, or requirements.

From Ink Pens to Computers: A Personal Look Back at Landmark Changes during 5 Decades as a Clinical Laboratory Scientist in U.S. Hemostasis Laboratories

In 2023, Seminars in Thrombosis and Hemostasis will be celebrating its 50^th anniversary, and similarly this will also mark my 5^th decade of working in, or association with, laboratories that perform hemostasis testing. My career started at a large military medical center, but I also worked at several other facilities, including military dispensaries, community hospitals, and a large academic institution. The difference between each type of hemostasis laboratory was as expected, with larger facilities having better instrumentation and more prolific test menus. However, whether one worked in a large academic center, or a small rural hospital, regulatory changes affected every clinical laboratory to the same degree. Advances in technology also eventually affected every hemostasis laboratory, but these salient changes were more likely to occur earlier at the larger institutions. As Seminars in Thrombosis and Hemostasis celebrates its 50^th anniversary, that milestone triggered recollection about those salient events that occurred during my own career in hemostasis testing. As such, I describe (my impression) the top ten landmark changes that altered laboratory practice at the facilities where I worked during the past 5 decades.

Effect of cocoa (Theobroma cacao L.) on platelet function testing profiles in patients with coronary artery disease: ECLAIR pilot study

INTRODUCTION

This prospective pharmacodynamic nutraceutical study assessed the effect of a 1-week trial of 30 g/day of 65% cocoa (dark chocolate) (Theobroma cacao L.) consumption intervention on platelet reactivity.

METHODS

Patients with stable coronary artery disease (CAD) (n=20) who were on maintenance dual antiplatelet therapy of aspirin (ASA) 81 mg/day and clopidogrel 75 mg/day were recruited. Platelet function was evaluated with the VerifyNow P2Y₁₂ reaction unit (PRU) and aspirin reaction unit (ARU) assays (Werfen, Bedford, Massachusetts, USA) and assessed prior to initiation of and after a 1-week trial of 30 g/day of 65% cocoa consumption intervention. Results were compared with a paired t-test.

RESULTS

Cocoa augmented the inhibitory effect of clopidogrel, demonstrated by a reduction of 11.9% (95% CI 5.7% to 18.0%, p value 0.001), significantly decreasing the PRU by 26.85 (95% CI 12.22 to 41.48, p value 0.001). The inhibitory effect of ASA was not impacted by cocoa, reflected by a non-significant reduction in ARU of 17.65 (95% CI 21.00 to 56.3, p value 0.351). No patients experienced any serious adverse events.

CONCLUSIONS

Cocoa augmented the inhibitory effect of clopidogrel but not ASA. This nutraceutical study could be potentially informative and applicable for patients with stable CAD. Further long-term studies are required to confirm these exploratory findings.

TRIAL REGISTRATION NUMBER

NCT04554901.

Towards 50 years of platelet function analyser (PFA) testing

The platelet function analyser (PFA) is a prevalent platelet function screening instrument, and comes in two models-the original PFA-100 and the contemporary PFA-200. The instruments have 'identical' output, being a 'closure time' (CT). Moreover, normal reference ranges provided by the manufacturer, for the specific test cartridges, are the same for both models. There are three different types of test cartridge: collagen/epinephrine (C/Epi), collagen/adenosine diphosphate (C/ADP), and "Innovance PFA P2Y" (only available in certain geographical locations). The PFA-100 was released in the mid 1990s, and so is approaching 50 years of age. The PFA-200, released in some locations in the mid 2010s, is destined to eventually replace the PFA-100, but is not yet available in the USA. The test system is highly sensitive to von Willebrand disease (VWD; C/Epi and C/ADP) and to aspirin therapy (C/Epi only), but only has moderate sensitivity to defects in platelet function and/or deficiencies in platelet number. Accordingly, recommendations for use for screening platelet function vary according to user experience. Some workers have alternatively used the PFA to assess thrombosis risk or pre-operative bleeding risk. In this review, we provide an overview of the history of PFA, and summarise its current clinical utility.

Harmonizing platelet function analyzer testing and reporting in a large laboratory network

INTRODUCTION

The platelet function analyzer (PFA) is a popular platelet function screening instrument, highly sensitive to von Willebrand disease (VWD) and to aspirin therapy, with moderate sensitivity to defects in platelet function and/or deficiencies in platelet number. There are two models, the original PFA-100 and the contemporary PFA-200. Normal reference ranges (NRRs) provided by the manufacturer are the same for both models, instead being based on the type of test cartridge, for which there are two main ones: collagen/epinephrine (C/Epi) and collagen/adenosine diphosphate (C/ADP).

METHODS

Comparative evaluations of PFA testing and reporting in six different sites of a large pathology network, aiming to harmonize NRRs and test reporting across all network sites. A separate comparative study of testing a range of samples (n > 150) on a PFA-100 versus that on a PFA-200. Review of contemporary literature.

RESULTS

Each site was identified to have a different reporting NRR, which after consolidating data permitted establishment of an agreed harmonized NRR for use across the network (C/Epi: 90-160; C/ADP: 70-124; based on n > 180). Similarly, each site reported and interpreted results in different ways, and after discussion and consolidation, a harmonized approach to interpretation and reporting was achieved. The separate comparative study of PFA-100 versus PFA-200 testing confirmed instrument equivalence.

CONCLUSION

We achieved harmonized NRRs and reporting for PFA testing across a large pathology network. Our approach may be useful for other laboratory networks wishing to harmonize PFA testing.

Chronic venous disease, platelet and haemostatic abnormalities contribute to the pathogenesis of pigmented purpuric dermatoses

Background

To investigate the aetiology of pigmented purpuric dermatoses (PPD).

Methods

63 patients with a provisional diagnosis of PPD were assessed. Skin biopsies were performed to confirm the clinical diagnosis. Haemostasis was assessed using platelet function analyser-100 (PFA-100), light transmission aggregometry (LTA), impedance aggregometry (Multiplate) and measurement of clotting times and clotting factors. Chronic venous disease (CVD) was assessed by duplex ultrasound. When not contraindicated, patients were advised to discontinue haemostatic-modifying drugs or supplements for 4 weeks after which the laboratory measurements were repeated and the clinical resolution of PPD was assessed. Subsequently, a cohort of patients identified with CVD underwent endovenous interventions and further resolution of PPD was assessed.

Results

CVD was found in 48 patients (76.2%) while haemostatic abnormalities were found in 36 (57.1%). 30 patients (47.6%) had concurrent CVD and haemostatic abnormalities. Modifiable risk factors such as the intake of platelet inhibitors or other drugs and supplements such as fish oil were identified in 53 patients (84.1%). These could be ceased in 35 patients of whom 28 (80.0%) achieved either complete or partial resolution of PPD. Treatment of the underlying CVD was performed in 18 patients resulting in complete or partial resolution in 17 (94.4%). In seven patients (11.1%), no CVD or haemostatic abnormalities were identified, and the risk factors included dietary factors such as excessive caffeine or soft drink consumption.

Conclusion

Haemostatic abnormalities and CVD contribute to the pathogenesis of PPD. Resolution of PPD in the vast majority of patients may be achieved by cessation of modifiable risk factors and in particular platelet-modifying drugs or supplements and treatment of the underlying venous disease.

Establishment of reference intervals for Platelet Function Analyzer -100 closure time in Algerian adults

INTRODUCTION

The Platelet Function Analyzer-100 (PFA-100) is a point of care instrument that simulates plug formation under high shear flow. The PFA-100 measures the time required to occlude the aperture in a biochemically active cartridge and is expressed in a term of closure time (CT). In Algeria, the reference values used in clinical laboratories are of Western origin. However, ethnic, genetic, dietary environmental, and diet differences between populations may affect reference intervals. We established the reference intervals of PFA-100 closure times in healthy Algerian adults according to the International Federation of Clinical Chemistry method, and we compared them with those of Western and Asian countries.

MATERIAL AND METHODS

We enrolled 303 healthy blood donors in the study. 218 subjects met inclusion criteria. We analyzed the blood sample on the PFA-100 for CT with both the collagen epinephrine and collagen ADP cartridges.

RESULTS

The reference intervals of PFA-100 collagen epinephrine CT and PFA-100 collagen ADP CT were 91-207 seconds and 71-144 seconds, respectively. Compared to Western and Asian populations, there were significant differences. The upper limits of CTs were higher for Algerians in this study. Our findings show that many healthy Algerians would be incorrectly identified as having a primary hemostasis abnormality according to the reference intervals of the manufacturer and scientific literature.

CONCLUSION

This report provides the first reference intervals for PFA-100 CTs in healthy Algerian adults. These results improve the accuracy of diagnosis and patient care in Algeria.

Uneventful epidural catheter removal in a patient with postoperative acute coronary syndrome receiving emergency triple antithrombotic therapy: a case report

BACKGROUND AND OBJECTIVES

Neuraxial hematoma is a rare complication of the epidural technique which is commonly used for high quality postoperative pain relief. In case of urgent initiation of multiple antithrombotic therapy, the optimal timing of epidural catheter removal and need for treatment modification may be quite challenging. There are no specific guidelines and published reports are scarce.

CASE REPORT

We present the uneventful removal of an indwelling epidural catheter in a patient who was put on emergency triple antithrombotic treatment with Low Molecular Weight Heparin (LMWH), aspirin and clopidogrel in the immediate postoperative period, due to acute coronary syndrome. In order to define the optimal conditions and timing for catheter removal, so as to reduce the risk of complications, various laboratory tests were conducted 3 hours after aspirin/clopidogrel intake. Standard coagulation tests revealed normal platelet count, normal prothrombin time and normal activated partial thromboplastin time, while Platelet Function Analysis (PFA-200) revealed abnormal values (increased COL/EPI and COL/ADP values, both indicating inhibition of platelet function). The anti-Xa level, estimated 4 hours after LMWH administration, was within therapeutic range. At the same time, Rotational Thromboelastometry (ROTEM) showed a relatively satisfactory coagulation status overall. The epidural catheter was removed 26 hours after the last dual antiplatelet dose and the next dose was given 2 hours after removal. Enoxaparin was withheld for 24 hours and was resumed after 6 hours. Neurologic checks were performed regularly for alarming signs and symptoms suggesting development of an epidural hematoma. No complications occurred.

CONCLUSION

Point-of-care coagulation and platelet function monitoring may provide a helpful guidance in order to define the optimal timing for catheter removal, so as to reduce the risk of complications. A case-specific management plan based on a multidisciplinary approach is also important.

Correlation between PlateletWorks® and PFA-100® for Measuring Platelet Function before Urgent Surgery in Patients with Chronic Antiplatelet Therapy

Hemostasis is crucial for reducing bleeding during surgical procedures. The points-of-care based on the platelet function test could be useful to minimize the complications related to chronic antiplatelet therapy during surgery. The present study is aimed at comparing two point-of-care platelet function devices-Platelet Function Analyzer PFA-100^® (Siemens Canada, Mississauga, ON, Canada) and Plateletworks^®(Helena Laboratories, Beaumont, TX, USA). Our objective is to evaluate if they provide comparable and useful information to manage anti-aggregate patients before surgery. We included patients with a femoral fracture receiving chronic antiplatelet therapy and a median age of 89 years (range from 70 to 98). A platelet function evaluation was performed on all patients before surgery using both devices-Plateletworks^® and PFA-100^®. The correlation between Plateletworks^® and PFA-100^® was performed using Cohen's Kappa coefficient. Twenty consecutive patients participated in the trial; 16 patients were under treatment with 75 mg/day of clopidogrel, three with >300 mg/day of acetylsalicylic acid (ASA), and only one was in treatment with both antiplatelet agents. Cohen's Kappa coefficient was 0.327 comparing PFA-100^®-ADP (adenosine diphosphate) and Plateletworks^® and, 0.200 comparing PFA-100^®-EPI (epinephrine) and Plateletworks^®. In conclusion, we found a weak concordance comparing PFA-100^® and Plateletworks^®. This could partially be due to the advanced age of the included patients. However, given the limited sample size, more studies are necessary to confirm these results.

Utility of the Platelet Function Analyzer in Patients with Suspected Platelet Function Disorders: Diagnostic Accuracy Study

Introduction  The platelet function analyzer (PFA) is widely used as a screening tool for bleeding disorders in various settings. The diagnostic performance regarding platelet function disorders (PFDs), which are among the most common inherited bleeding disorders, is however still elusive. We aimed to assess the diagnostic value of PFA for PFD in clinical practice.

Methods  Comprehensive clinical and laboratory data of all consecutive patients referred to a specialized outpatient between January 2012 and March 2017 with a suspected bleeding disorder were prospectively recorded. The diagnostic work-up was performed according to a prespecified protocol following current guidelines and platelet function was tested using light transmission aggregometry as well as flow cytometry.

Results  Five hundred and fifty-five patients were included (median age 43.7 years; interquartile range [IQR] 29.3, 61.7; 66.9% female). Possible PFD was diagnosed in 64 patients (11.5%) and confirmed PFD in 54 patients (9.7%). In patients with confirmed PFD, median closure times were 107 seconds (ADP or adenosine diphosphate; IQR 89, 130) and 169 seconds (EPI; IQR 121, 211). In patients without bleeding disorders, PFA closure times were 96 seconds (ADP; IQR 83, 109) and 137 seconds (EPI; IQR 116, 158). The sensitivity was 19.5% in case of PFA ADP (95%CI 12.6, 30.0; specificity 86.4%; 95% CI 82.4, 89.8), and 44.3% in case of PFA EPI (95% CI 34.9, 53.9; specificity 75.6%; 95% CI 70.8, 79.9).

Conclusion  The diagnostic performance of PFA for PFD was moderate to poor. Our results do not support the utilization of PFA for screening of PFD in clinical practice.

The role of platelet function analyzer-200 in predicting perioperative bleeding risk

BACKGROUND/AIMS

Various preoperative screening tests, such as platelet count, prothrombin time, activated partial thromboplastin time, and bleeding time, have been widely used to evaluate the risk of bleeding during surgery. Use of platelet function analyzer (PFA)-100/200 for assessing platelet function instead of bleeding time is increasing. However, its role in predicting the perioperative risk of bleeding remains controversial.

METHODS

Data of 703 patients who underwent surgery under general anesthesia were retrospectively analyzed. Preoperative platelet function was measured using PFA-200 system and the association with intraoperative bleeding was assessed. Additionally, other variables that could affect PFA-200 results were assessed by logistic regression analysis.

RESULTS

Collagen/epinephrine (COL/EPI) test was prolonged in 199/703 (28.3%) patients (EPI group), while 99/212 (46.7%) patients showed COL/adenosine diphosphate test abnormalities. Bleeding over 300 mL during surgery occurred in 14.3% and 20.1% of patients in the normal and EPI groups, respectively (p = 0.058). In addition, red blood cell transfusion within 72 hours after surgery rate was significantly higher in the EPI group than in the normal group (31.7% vs. 23.4%, p = 0.024). In multivariate logistic analysis, prolongation closure time with COL/EPI (p = 0.068) was marginally associated with risk of bleeding during surgery. Furthermore, PFA-200 results were influenced by various factors, such as nonsteroidal anti-inflammatory drug use, blood group, hematocrit, and time of blood collection.

CONCLUSION

Preoperative PFA-200 test may be helpful in predicting the risk of perioperative bleeding. However, its results should be carefully interpreted because they are affected by several factors.

Platelet Function: Meloxicam Intravenous in Whole Blood Samples From Healthy Volunteers

Nonsteroidal anti‐inflammatory drugs (NSAIDs) are effective treatments for pain but may induce bleeding events due to platelet dysfunction associated with inhibition of cyclooxygenase (COX)‐1 impairing thromboxane production. An intravenous nanocrystal formulation of meloxicam, a COX‐2 preferential nonsteroidal anti‐inflammatory drug, is under development for the treatment of moderate to severe pain. This single‐center ex vivo study evaluated the effect of meloxicam intravenous and ketorolac on platelet function in whole blood samples from healthy volunteers. Each whole blood sample was aliquoted to allow analysis using a platelet function analyzer under negative control (untreated), positive control (2 therapeutic ketorolac concentrations), and meloxicam intravenous (1 therapeutic, 3 supratherapeutic concentrations) using both collagen with epinephrine and collagen with adenosine diphosphate reagent cartridges. The platelet function analyzer determines closure time by simulating platelet adhesion and aggregation following vascular injury. The final analysis set included data from 8 subjects. The collagen with adenosine diphosphate analysis (sensitive to thrombocytopathies) showed no significant differences in closure time for meloxicam‐ or ketorolac‐treated samples and untreated control. The collagen with epinephrine analysis (sensitive to aspirin‐induced platelet abnormalities) produced no significant difference in closure time between any meloxicam concentration and untreated control. Ketorolac was associated with significantly longer closure times vs untreated control at both the 2.5‐ and 5‐µg/mL concentrations (P = .003 and .0257, respectively) and vs meloxicam at several concentrations. Similar results were observed when all analyzed samples were included. Meloxicam intravenous had no significant effect on closure times at therapeutic or supratherapeutic concentrations in this ex vivo study.

Effectiveness of Platelet Function Analyzer-100 for Laboratory Detection of Anti-Platelet Drug-Induced Platelet Dysfunction

BACKGROUND

High on-treatment platelet reactivity (HTPR) is the phenomenon wherein patients exhibit normal platelet activity in laboratory testing despite adequate adherence to anti-platelet treatment. We investigated the detection rates of Platelet Function Analyzer (PFA)-100 (Dade Behring AG, Düdingen, Switzerland) for drug-induced platelet dysfunction and analyzed potential contributors to HTPR with practical PFA-100 data over six years.

METHODS

We used data from 6,957 patients who underwent PFA-100 testing after receiving aspirin, clopidogrel, or non-steroidal anti-inflammatory drugs (NSAIDs). Of these, 6,163 patients were tested with only the collagen/epinephrine cartridge (Col/EPI) of PFA-100; 794 were tested with both Col/EPI and the collagen/ADP cartridge (Col/ADP). We calculated PFA-100 closure time (CT) for each drug and compared the clinical and laboratory characteristics of the patients with prolonged CTs and normal CTs (i.e., HTPR).

RESULTS

In Col/EPI, 73.2% (365/499), 72.6% (390/537), and 55.3% (3,442/6,228) patients showed prolonged CTs for aspirin, clopidogrel, and NSAIDs, respectively. In Col/ADP, prolonged CTs were observed in 37.4% (34/91), 43.2% (35/81), and 29.6% (200/676) of patients receiving aspirin, clopidogrel, and NSAIDs, respectively. Of the patients tested with both cartridges, 88.9% (48/54), 95.3% (41/43), and 89.0% (577/648) of the patients receiving aspirin, clopidogrel, and NSAIDs had prolonged CTs, and 10.0% (79/794) showed normal CTs regardless of drugs. For clopidogrel users (both cartridges), there were more patients with malignancies in the normal CT than prolonged CT group.

CONCLUSIONS

PFA-100 is not sufficiently effective for laboratory screening of drug-induced platelet dysfunction. Malignancy may contribute to clopidogrel-related HTPR in PFA-100.

The in vitro effect of the new antithrombotic drug candidate ALX-0081 on blood samples of patients undergoing percutaneous coronary intervention

Compound ALX-0081 is a bivalent humanised Nanobody® that binds the A1-domain of von Willebrand factor (VWF) with high affinity. Consequently, it can block the interaction between VWF and its platelet-receptor- glycoprotein Ib, which leads inevitably to formation of arterial thrombi. It was the objective of this study to assess the in vitro effects of ALX-0081 on platelet adhesion and aggregation in coronary artery disease (CAD) patients to determine the optimal concentration of ALX-0081 and the effect of co-medication. We included nine CAD patients, who were scheduled for elective percutaneous coronary intervention (PCI), and 11 healthy volunteers. At admission all patients received aspirin, clopidogrel and heparin. Blood was drawn 24 hours (h) before and 1 h after start of the PCI procedure and was subsequently spiked with different concentrations of ALX-0081 or buffer. The efficacy of ALX-0081 was assessed by in vitro experiments: flow chamber experiments, ristocetin-induced platelet aggregation (RIPA), and the platelet function analyser (PFA-100TM). VWF levels in CAD patients were significantly higher than in healthy controls. During PCI VWF levels did not rise. In all in vitro experiments, ALX-0081 led to complete inhibition of platelet adhesion and aggregation. However, the required effective concentration was higher in patients than in controls and was related to plasma VWF levels. In conclusion, ALX-0081 is able to completely inhibit in vitro platelet adhesion and aggregation in CAD patients scheduled for elective PCI. The efficacy of ALX-0081 is not influenced by PCI or co-medication. However, due to higher VWF levels in CAD patients a higher effective concentration of ALX-0081 was required than in healthy individuals.

Screening for platelet function disorders with Multiplate and platelet function analyzer

Light transmission aggregation (LTA) is the gold standard for the diagnosis of platelet function disorders (PFDs), but it is time-consuming and limited to specialized laboratories. Whole-blood impedance aggregometry (Multiplate) and platelet function analyzer (PFA) may be used as rapid screening tools to exclude PFDs. The aim of this study is to assess the diagnostic performance of Multiplate and PFA for PFDs, as detected by LTA.Data from preoperative patients, patients referred to the hematologist for bleeding evaluation, and patients with a diagnosed bleeding disorder were used. PFDs were defined as ≥2 abnormal LTA curves. Diagnostic performance of Multiplate and PFA for detecting PFDs was expressed as sensitivity and specificity. The ability of Multiplate agonists and PFA kits to detect corresponding LTA curve abnormalities was expressed as area under the receiver operating characteristic curve. Prevalence of PFDs was 16/335 (4.8%) in preoperative patients, 10/54 (18.5%) in referred patients, and 3/25 (12%) in patients with a diagnosed bleeding disorder. In preoperative and referred patients, the sensitivity of Multiplate and PFA for detecting mild PFDs varied between 0% and 40% and AUCs for detecting corresponding LTA curve abnormalities were close to 0.50. In patients with a diagnosed bleeding disorder, both assays could detect Glanzmann thrombasthenia (GT) with sensitivity of 100% and AUCs of 0.70-1.00. Multiplate and PFA cannot discriminate between preoperative and referred patients with and without mild PFDs, meaning that they cannot be used as screening tests to rule out mild PFDs in these populations. Both Multiplate and PFA can detect GT in previously diagnosed patients.

Variables That Affect Results of PFA-100 in a Group of Healthy Blood Donors in the Slovak Population

Background: The platelet function analyzer (PFA-100) is a system analyzing platelet function determined for detection of the functional inherited and acquired platelet disorders, screening of von Willebrand disease (vWD) and recently also considered as useful for monitoring of antiplatelet treatment. The PFA-100 test uses a high shear flow system to simulate in vitro the conditions to which platelets are subjected at the site of a damaged blood vessel wall.

Aim of study: We decided to establish the reference intervals of PFA closure time (CT) in the Slovak population of healthy blood donors.

Patients and methods: Fifty age and gender matched healthy blood donors were enrolled in the study. We investigated the relationships between PFA-100 CT, gender and ABO blood groups.

Results: The reference intervals for CT measured on CEPI (collagen/epinephrine) and CADP (collagen/adenosine diphosphate) cartridge in 3.2% citrated blood were 86 - 199 sec. and 42 - 119 sec., respectively. Blood group O was associated with significantly longer CEPI CT (p<0.05) compared to non - O groups. The prolongation of CADP CT in blood donors with blood group O was without significance. The influence of gender as another variable analyzed with CT has not been evaluated as statistically significant.

Conclusion: PFA-100 CT should be interpreted carefully with consideration of both the patient’s clinical presentation and laboratory variables such as ABO blood group.

Clinical utility of closure times using the platelet function analyzer-100/200

The "platelet function analyzer" (PFA)-100 was first introduced to us in 1995. Since then, the instrument has appeared in over 50 reviews and almost 1000 publications. Recently, the PFA-100 has been "upgraded" to the PFA-200, which has transformed the user interface and electronic management, but retained the fundamental mechanics, and essentially provides the same results. The PFA-100/200 has conceivable clinical utility to screen for von Willebrand Disease (VWD) and platelet disorders, and in monitoring desmopressin (DDAVP) therapy in both, and possibly anti-platelet therapy. Its great strengths are its usage simplicity and sensitivity to conditions affecting primary hemostasis. However, as a "global" test, its limitation is that closure time (CT) test results are neither predictive of, nor specific for, any individual disorder. However, utilized properly, the PFA-100/200 reflects a valuable addition to hemostasis laboratories involved in identification or therapeutic-monitoring of disorders of primary hemostasis.

Effect of shear-induced platelet activation on red blood cell aggregation

Mechanical shear stress is one of the important factors for platelet activation. Although shear stress has been frequently utilized in many applications of diagnostic bio-equipment, there has been little consideration as to whether shear stress induces platelet activation and consequently alters hemorheological characteristics. Therefore, we investigated the effect of shear-induced platelet activation on red blood cell (RBC) aggregation. The hypothesis of the present research is as follows: Platelets activated by high shear stress secrete substances, which can affect hemorheological characteristics to promote RBC aggregation. In our study, an increase in RBC aggregation indices (critical shear stress (CSS) and aggregation index (AI)) by shear-induced platelet activation was observed. Significantly, an increase of 19% in CSS was observed. However, deformability remained unchanged. These phenomena could be a result of the increased cellular adhesion force on RBC membranes due to secreted substances from activated platelets. Therefore, since high shear application results in the unexpected effect on RBC aggregation, conditions for shear application in diagnostic bio-equipment are to be carefully determined.

A simple method for activating the platelets used in microfluidic platelet aggregation tests: Stirring-induced platelet activation

High-shear stimulation is well known as one of the key factors affecting platelet activation and aggregation, which can lead to the formation of a thrombus. In one of our previous studies, we introduced migration distance-based platelet function analysis in a microfluidic system. In this study, we set out to examine the effects of stirring on shear-induced platelet activation and aggregation in a chamber system by using a rotating stirrer. We found that the rotating stirrer caused not only rotational shear flow but also a strong radial secondary flow. The latter flow led to efficient mixing in the chamber. Moreover, the rotational flow led to the generation of shear stress, the magnitude of which can be controlled to activate the platelets. Activated platelets tend to aggregate themselves. The maximum platelet aggregation was observed at a critical shear rate of 3100 s-1, regardless of the stirrer shape. Furthermore, the time taken to attain maximum aggregation was significantly shortened when using a wide stirrer (30 s) instead of a narrow one (180 s). When using a flat stirrer, the non-uniform shear field in the chamber system was resolved with the radial secondary flow-induced mixing; thus, most of the platelets were homogenously activated. The stirring-induced platelet activation mechanism was experimentally confirmed in a microfluidic system for a platelet aggregation test while monitoring the migration distance until the microfluidic channel is occluded. Our findings indicate that the present system, consisting of a rotating stirrer and a confined chamber, provides effective shear stimulation for activating platelets and inducing platelet aggregates.

Bleeding Diatheses: Approach to the Patient Who Bleeds or Has Abnormal Coagulation

Many complex elements contribute to normal hemostasis, and an imbalance of these elements may lead to abnormal bleeding. In addition to evaluating medication effects, the hematologist must evaluate for congenital or acquired deficiencies in coagulation factors and platelet disorders. This evaluation should include a thorough bleeding history with careful attention to prior hemostatic challenges and common laboratory testing, including coagulation studies and/or functional platelet assays. An accurate diagnosis of a bleeding diathesis and selection of appropriate treatment are greatly aided by a basic understanding of the mechanisms of disease and the tests used to diagnose them.

Evidence Based Coagulation Monitors: Heparin Monitoring, Thromboelastography, and Platelet Function

The hemostatic management of patients undergoing cardiac surgery is a unique challenge. Since its inception, cardiopulmonary bypass (CPB) has required meticulous attention to maintaining adequate anticoagulation. New anticoagulants and alternative monitoring techniques present an opportunity to investigate potential advances in the area of anticoagulation for CPB. Hemostasis after CPB is still a vexing problem, and the addition of antiplatelet medication to the platelet defect already incurred during CPB has led to hemorrhagic complications in cardiac surgery. The two opposing processes of anticoagulation and hemostasis must be managed carefully and modified with respect to the patient's hematologic status and desired hemostatic outcome. Cardiac surgical patients consume a much larger fraction of perioperative blood transfusions than the percentage of the surgical population they represent. Thus, during CPB, careful attention must be paid to optimal anticoagulation, platelet quiescence, biocompatible circuitry and interventions, and to monitoring hemostasis. The multifactorial etiology of the CPB-induced hemostatic defect requires a multimodal approach to blood conservation and hemostasis monitoring, including heparin maintenance and sophisticated point-of-care hemostasis monitoring. Each technology has its own attributes and each may be suitable for different populations based upon the expected defects being measured. This article reviews the evidence supporting the use of point-of-care monitors in coagulation and hemostasis management in cardiac surgical patients.

Platelet Function and Cardiopulmonary Bypass

Cardiopulmonary bypass (CPB) is a nonphysiologic state that has many detrimental effects on a patient's hemostatic integrity. Exposure to the extracorporeal circuit and subsequent activation of the coagulation and fibrinolytic systems are factors that contribute to morbidity and mortality in cardiac surgical patients. These effects can be prevented in part or appropriately treated if practitioners understand the basic mecha nisms. This article reviews the effects of CPB on platelet function, the relationship of platelet function to post operative bleeding, the monitors available to measure platelet function, and the impact of antiplatelet therapy on bleeding in cardiac surgery.

Platelets as Predictors of Vascular Risk: Is There a Practical Index of Platelet Activity?

Activated platelets play a role in the pathogenesis of coronary heart disease (CHD). Following activation, platelets change shape, aggregate, and release several bioactive substances. The aim of this review is to identify if there is a simple and cost-effective method that indicates platelet activation and predicts the risk of CHD and vascular events. The rationale for identifying high-risk patients is to reduce their risk of vascular events by administering appropriate and effective antiplatelet treatment, like aspirin, clopidogrel, or combination regimens. Many laboratory tests estimating platelet activity have been described. Some are relatively simple, such as spontaneous or agonist-induced platelet aggregation. Other tests include measuring the mean platelet volume (MPV) or plasma soluble P-selectin levels. Some more complex tests include flow cytometry to determine platelet GP Ilb/Illa receptors, platelet surface P-selectin, plateletmonocyte aggregates, and microparticles. Only few prospective studies assessed the predictive value of platelet activation in healthy individuals. Although the MPV seems an 'easy method, there are insufficient data supporting its ability to predict the risk of a vascular event in healthy adults. Platelet aggregation, in whole blood or in platelet-rich plasma was not consistently predictive of vascular risk. Soluble P-selectin measurement is a promising method but it needs further evaluation. Flow cytometry methods are costly, time-consuming, and need specialized equipment. Thus, they are unlikely to be useful in estimating the risk in large numbers of patients. There is as yet no ideal test for the detection of platelet activation. Each currently available test has merits and disadvantages. Simple methods such as the MPV and the determination of platelet release products need further evaluation.

A Practical Concept for Preoperative Identification of Patients with Impaired Primary Hemostasis

The findings of a large prospective study designed to identify primary and/or secondary hemostatic disorders before surgical interventions are presented. A total of 5649 unselected adult patients were enrolled to identify impaired hemostasis before surgical interventions. Each patient was asked to answer a standardized questionnaire concerning bleeding history. Activated partial thromboplastin time (aPTT), prothrombin time (PT), and platelet counts (PC) including PFA-100 (platelet function analyzer): collagen-epinephrine (C/E), and collagen-ADP (C/ADP) were routinely done in all patients. Additional tests, bleeding time (BT), and von Willebrand factor (vWF: Ag) were performed only in patients with a positive bleeding history and/or evidence of impaired hemostasis; e.g., drug ingestion. The bleeding history was negative in 5021 patients (88.8%) but positive in the remaining 628 (11.2%). Impaired hemostasis could be verified only in 256 (40.8%) of these patients. The vast majority were identified with PFA-100: C/E (n=250; 97.7%). The other six patients with impaired hemostasis were identifiable solely based on the PT (n=2), PFA-100: C/ADP (n=2), and vWF: Ag (n=2). The PFA-100: C/ADP detected 199 patients (77.7%). The only abnormality found among patients with a negative bleeding history was a prolonged aPTT due to lupus anticoagulant in nine patients (0.2%). The sensitivity of the PFA-100: collagen-epinephrine was the highest (90.8%) in comparison to the other screening tests (BT, aPTT, PT, vWF: Ag). The positive predictive value of the PFA-100: collagen-epinephrine was high (81.8%), but the negative predictive value was higher (93.4%). The use of a standardized questionnaire and, if indicated, the PFA-100: C/E and/or other specific tests not only ensure the detection of impaired hemostasis in almost every case but also a significant reduction of the cost.

Approach to the Assessment of Platelet Function: Comparison between Optical-based Platelet-rich Plasma and Impedance-based Whole Blood Platelet Aggregation Methods

Platelet aggregation studies play an important role in the assessment of hereditary and acquired platelet function defects. The first aggregation test introduced into laboratory practice used platelet-rich plasma (PRP) where aggregation was detected by an optical method. The assessment of platelet function using whole blood (WB) aggregation by an impedance method followed up nearly 20 years later. The WB impedance aggregation assay appears to be superior to the optical method because it 1) evaluates platelets in a physiologic milieu in the presence of red and white blood cells, which are known to modulate platelet function; 2) is faster; 3) has higher sensitivity; and 4) does not require centrifugation, thus avoiding injury to platelets and loss of giant thrombocytes. These two assays were compared. Clearly, the WB impedance aggregation methodology has many advantages over the optical PRP assay for the assessment of the hyperactive platelet syndrome and the effects of anti-platelet drugs.

Antiplatelet Effect of Sequential Administration of Cilostazol in Patients with Acetylsalycilic Acid Resistance

BACKGROUND

Acetylsalicylic acid (ASA) resistance in patients with coronary artery disease is an important medical problem that can affect treatment decision-making and outcomes. Cilostazol has been investigated to determine its effectiveness in patients with acetylsalicylic acid resistance. The aim of this study was to evaluate the antiplatelet efficacy of sequential administration of CLZ in patients with ASA resistance.

METHODS

A total of 180 patients were enrolled in our study. Patients with stable coronary artery disease were first given orally ASA 100 for 10 days, followed by collagen/epinephrine induced closure time (CTCEPI) measurements. Those who were found to be resistant to orally 100 mg of ASA were given orally 300 mg of ASA for an additional 10 days after which we repeated CTCEPI measurements. Those patients with resistance to orally 300 mg ASA were then given CLZ at a daily dose of orally 200 mg for 10 days followed by a final CTCEPI measurement.

RESULTS

The rate of resistance to 100 mg ASA was 81/180 (45%) compared to a rate of 35/81 (43.2%) with 300 mg ASA. Of the 35 patients found to be resistant to 300 mg ASA, 22 (62.9%) also failed to respond to CLZ treatment. Overall, sequential administration of 300 mg ASA and 200 mg CLZ resulted in a reduction in the number of non-responders from 45% to 12.2%.

CONCLUSIONS

Initiation of CLZ could be of benefit in some patients with ASA-resistance for whom an effective anti-aggregant effect is of clinical importance.

Verifying the performance characteristics of the TEG5000 thromboelastogram in the clinical laboratory

OBJECTIVE

To verify the manufacturer performance claims of the TEG5000 with traditional laboratory methods.

MATERIALS AND METHODS

Samples were concurrently measured using the TEG5000 analyzer and either PT, APTT, fibrinogen, factor activities, platelet count, or platelet function testing using whole blood or platelet-rich plasma methods.

RESULTS

Within-run imprecision yielded coefficient of variation (CV) of <5%. There was no correlation of PT or APTT with R time. Only Factor VIII and factor XII activity significantly correlated with R time. There was significant correlation between k and angle with FBG, PLT count, and factor levels. There was weak inverse correlation between angle results and measures of platelet function. All laboratory methods were significantly correlated with MA. There were significant differences between citrated whole blood and fresh citrated plasma for angle and MA, and between fresh and frozen plasma for R time and MA. We demonstrated a high % inhibition noted with normal, drug naïve donors, especially with ADP PLT mapping (50% inhibition), but less so with AA PLT mapping (20% inhibition). For TEG platelet mapping, 19/22 (86.3%) and 17/22 (77.3%) results were concordant with traditional aggregation results.

CONCLUSION

We demonstrated both the lack of, and strong correlation between laboratory tests and the TEG parameters.

The effects of haemodilution with hydroxyethyl starch 130/0.4 solution on coagulation as assessed by thromboelastography and platelet receptor function studies in vitro

This study evaluated the effects of haemodilution with either 6% hydroxyethyl starch (HES) 130/0.4 (Voluven(®)) or 0.9% normal saline (NS) on blood coagulation in vitro. Haemodilution with 6% HES 130/0.4 impaired coagulation, as indicated by the changes in thromboelastographic parameters k-time, α-angle and maximum amplitude. Light transmission aggregometry and multiple electrode aggregometry demonstrated that impaired platelet receptor function occurred only at high levels of haemodilution (40%) with both fluids, but there was no significant difference between the two fluids (P=0.05). The thromboelastographic functional fibrinogen assay showed that the fibrinogen component of clot strength was significantly impaired with haemodilution with HES 130/0.4 compared with haemodilution with NS (whole blood [14.4 ± 4.6 mm] versus 40% HES dilution [3.7 ± 1.9], [P=0.001]; versus 40% NS dilution [10.4 ± 4.6], [P=0.129]). These findings suggest that there is little difference between HES or NS in relation to coagulation or platelet function during minor or moderate haemodilution, but at high levels of haemodilution with HES, fibrinogen activity is more impaired compared with NS.

Interaction of clopidogrel and statins in secondary prevention after cerebral ischaemia - a randomized, double-blind, double-dummy crossover study

AIMS

Variability in responsiveness to clopidogrel is a clinical problem in secondary prevention after cerebral ischaemia which has been suggested to be linked to competitive metabolization of clopidogrel and cytochrome P450 (CYP) 3A4-oxidated statins such as simvastatin. We assessed the hypothesis that simvastatin, in contrast to CYP 2C9-metabolized fluvastatin, reduces clopidogrel-mediated platelet inhibition.

METHODS

We performed a randomized, double-blind, double-dummy, two period crossover study in 13 patients with cerebral ischaemia (8F, 5 M), aged 64.1 ± 8.0 years (mean ± SD). After a 14 day period in which all patients received 75 mg clopidogrel day(-1) , patients additionally received either 20 mg simvastatin day(-1) or 80 mg fluvastatin day(-1) for 14 days. Regimens were crossed over after a 14 day wash-out period and switched regimens were continued for another 14 days. Platelet aggregation, clopidogrel active metabolite (CAM) plasma concentrations and routine laboratory parameters including prothrombin time (PT) Quick percent value were assessed at baseline and following each treatment phase.

RESULTS

Clopidogrel reduced platelet aggregation in all patients as expected. Platelet aggregation and CAM plasma concentrations were unaltered when simvastatin or fluvastatin was added to clopidogrel. Simvastatin decreased PT Quick percent value (decrease from 109 ± 10.5% to 103 ± 11%, P < 0.05) when combined with clopidogrel but there was no such change following treatment with fluvastatin and clopidogrel.

CONCLUSIONS

Our data indicate that treatment with CYP 3A4-metabolized simvastatin does not jeopardize clopidogrel-mediated inhibition of platelet aggregation. After co-administration of simvastatin and clopidogrel we observed a decrease in the PT Quick percent value which could be due to simvastatin-induced reduction of activity of prothrombin fragment 1 + 2.