Which is the best anticoagulant for whole blood aggregometry platelet function testing? Comparison of six anticoagulants and diverse storage conditions

Desmopressin, Misoprostol, nor Carboprost Affect Platelet Aggregability Following Traumatic Brain Injury and Aspirin

INTRODUCTION

Desmopressin (DDAVP) has been utilized clinically in patients taking aspirin (ASA) to improve drug-induced platelet dysfunction. Misoprostol and carboprost, prostaglandin analogs commonly used for postpartum hemorrhage, may also induce platelet aggregation. The aim of this study was to determine the effects of DDAVP, misoprostol, and carboprost administration on platelet aggregability following traumatic brain injury (TBI) in mice treated with ASA.

METHODS

Male C57BL/6 mice were randomized into seven groups (n = 5 each): untouched, ASA only, Saline/TBI, ASA/TBI, ASA/TBI/DDAVP 0.4 μg/kg, ASA/TBI/misoprostol 1 mg/kg, and ASA/TBI/carboprost 100 μg/kg. TBI was induced via a weight drop model 4-h after ASA (50 mg/kg) gavage. Mice were given an intraperitoneal injection of DDAVP, misoprostol, or carboprost 10 minutes after TBI. In vivo testing was completed utilizing tail vein bleed. Mice were sacrificed 30-min posttreatment and blood was collected via cardiac puncture. Whole blood was analyzed via Multiplate impedance aggregometry, rotational thromboelastometry, and TEG6s.

RESULTS

Mice receiving misoprostol after ASA/TBI demonstrated decreased tail vein bleeding times compared to ASA only treated mice. However, mice treated with misoprostol following ASA and TBI demonstrated decreased platelet aggregability compared to untouched mice and TBI only mice within the arachidonic acid agonist pathway. By contrast, DDAVP and carboprost did not significantly change platelet aggregability via adenosine diphosphate or arachidonic acid following ASA and TBI. However, DDAVP did decrease the platelet contribution to clot via rotational thromboelastometry.

CONCLUSIONS

Reversal of medication-induced platelet inhibition has become increasingly controversial after TBI. Based on these results, DDAVP, misoprostol, nor carboprost consistently improve platelet aggregability following TBI in those also treated with ASA.

Extended sample storage for platelet function testing in healthy dogs

BACKGROUND

Platelet function testing is important for monitoring the effects of antiplatelet therapy but is not readily used due to time constraints for testing and the need for specialized equipment.

OBJECTIVES

This study evaluated the effects of various storage methods on selected platelet function tests to determine if delayed platelet function testing is feasible in canine blood samples. Our hypotheses were that platelet function would not decline during storage and, thus, no differences in test results would be found over time.

METHODS

Thirteen healthy dogs were studied. Citrated blood samples were tested with a Platelet Function Analyzer-200 (PFA), which mimics high-shear conditions, using P2Y and CADP cartridges, after being held at room temperature for 2 h and refrigerated for 24 and 48 h. Plateletworks (PW), which measures aggregation based on platelet counting, was performed on an optical hematology analyzer using 10-min-old native samples, citrated samples held at room temperature for 3-4 h and refrigerated for 24 and 48 h, and samples stored in the preservative solution, AGGFix, up to 7 days.

RESULTS

PFA closure times increased with storage, especially with the P2Y cartridge. Median aggregation with fresh PW was 94%, and this was maintained at all time points (range of median values 88%-94%). Most samples showed decreased, yet still robust (>70%), aggregation with longer storage. Spontaneous aggregation in citrate was noted in most dogs. AGGFix stabilized platelet aggregates to allow for delayed testing.

CONCLUSIONS

Delayed platelet function testing is feasible, but ranges of expected values may differ from tests using fresh samples.

Platelet Function Testing: Update and Future Directions

Platelets play a key role in maintaining normal hemostasis and are also recognized as partners in the development of arterial thrombosis. Today, platelet function testing is used for very different clinical purposes; first, for investigation of platelet dysfunction in acute bleeding and diagnosis of platelet disorders in patients with long-lasting bleeding tendency, and second, for testing the efficacy of antiplatelet therapy in patients with increased thromboembolic risk. Moreover, it has been discussed whether platelet function testing can be used for prediction of bleeding risk (e.g., prior to major surgery). Ever since light transmission aggregometry was introduced, laboratories around the world have worked on testing platelet function, and during the last decades a wide range of new methods has emerged. Besides the clinical utility of platelet function testing, the present review summarizes the test principles and advantages and disadvantages of the different methods, depending on the purpose for which it is to be used. A critical step in investigation of platelet function is the preanalytical factors that can substantially affect test results. Therefore, this review also provides an overview of preanalytical variables that range from patient-related factors such as smoking, coffee, and exercise prior to blood sampling to selection of anticoagulant, needle gauge, and time from blood sampling to analyses. Finally, this review outlines further perspectives on platelet function testing for clinical practice and for research purposes.

Protocol for the Investigation of Plasma and Whole Blood Clot Property of Fibrin Fiber Thickness Using Scanning Electron Microscopy

Blood clot formation represents a key component of the coagulation process for preventing excessive hemorrhage. The structural characteristics of blood clots are associated with their strength and susceptibility to fibrinolysis. Scanning electron microscopy is a technique that allows for state-of-the-art image capture of blood clots, providing visualization of topography, fibrin thickness, fibrin network density, and blood cell involvement and morphology. In this chapter, we provide a detailed protocol for characterization of plasma and whole blood clot structure using SEM, covering the spectrum from blood collection, in vitro clot formation, sample preparation for SEM, imaging, and image analysis, specifically focusing on the measurement of fibrin fiber thickness.

Platelet function testing using the Multiplate analyzer after administration of aspirin in Aachen minipigs

Knowledge of platelet function in pigs and the effectiveness of antiplatelet therapy is important to ensure proper transferability from animal studies to humans. Our aim was to (1) characterize baseline platelet function of Aachen minipigs using the bedside Multiplate analyzer, (2) compare baseline platelet function with Göttingen minipigs, and (3) characterize platelet inhibition within the first 5 minutes after intravenous administration of acetylsalicylic acid (ASA). We characterized the baseline platelet function and hematological parameters in 9 Aachen minipigs. Historical data of 8 unmedicated Göttingen minipigs were used for comparison of baseline values. Platelet inhibition in Aachen minipigs was tested 1-5 minutes after intravenous administration of 500 mg ASA. Multiplate examinations included the following tests: ASPI test (to assess the effect of ASA), adenosine-diphosphate-test (ADP test) and thrombin receptor activating peptide test (TRAP test). Median values and interquartile range (IQR) of the Multiplate baseline tests in Aachen minipigs were as follows: ASPI: 39 U (IQR = 21-71), ADP: 70 U (IQR = 48-73), and TRAP: 8 U (IQR = 6-9), whereas the values in Göttingen minipigs were as follows: ASPI: 70.5 U (IQR = 60-78), ADP: 51 U (IQR = 45-66), and TRAP: 6.5 U (IQR = 4-8). ASPI values of Göttingen minipigs were significantly higher than those of Aachen minipigs (p = 0.046). Intravenous administration of ASA in Aachen minipigs resulted in significant platelet inhibition after 1 minute, which remained stable over a period of 5 minutes (p≤0.038). Aachen minipigs appeared to have a high variance in arachidonic acid-mediated platelet aggregation. In Aachen minipigs, intravenous ASA administration resulted in immediate platelet inhibition.

Polysaccharide-protein complex from coelomic fluid of Dendrobaena veneta earthworm exerts a multi-pathway antiplatelet effect without coagulopathy and cytotoxicity

There is a pressing need to identify novel antiplatelet agents, an alternative to acetylsalicylic acid and thienopyridines, to broaden the prevention of cardiovascular events, the leading cause of global morbidity and mortality. Invertebrate coelomocytes structurally and functionally resemble the thrombocyte-like cells of vertebrates; therefore, the coelomic fluid in which they are suspended may contain agents controlling their clumping abilities. However, whether coelomocytes-free coelomic fluid may also affect human platelet activities was not a subject of any study. This study aimed to screen the in vitro antiplatelet and anticoagulant activities of the polysaccharide-protein complex from Dendrobaena veneta coelomic fluid (25-100 µg/mL) (PPC-DV). All tested fluid concentrations induced significant (42.4-52.5%) inhibition of adenosine-5'-diphosphate (ADP)-induced aggregation of human platelets at a level comparable to that of 140 µmol/L acetylsalicylic acid. Its relevant antiplatelet effect (27.2-45.9%) was also evidenced in the thrombin receptor-activating peptide-6 (TRAP-6) assay. Moreover, 50 and 100 µg/mL of PPC-DV inhibited arachidonic acid-inducible aggregation. No coagulopathic or cytotoxic effects of PPC-DV were observed. The study indicates that PPC-DV, at a concentration of at least 50 µg/mL, exerts a favorable antiplatelet effect by targeting at least three pathways (P2Y₁₂ receptor, cyclooxygenase-1, and protease-activated receptor-1), justifying further experimental and clinical investigations on its use in cardiovascular disease prevention.

Screening and diagnosis of inherited platelet disorders

Inherited platelet disorders are important conditions that often manifest with bleeding. These disorders have heterogeneous underlying pathologies. Some are syndromic disorders with non-blood phenotypic features, and others are associated with an increased predisposition to developing myelodysplasia and leukemia. Platelet disorders can present with thrombocytopenia, defects in platelet function, or both. As the underlying pathogenesis of inherited thrombocytopenias and platelet function disorders are quite diverse, their evaluation requires a thorough clinical assessment and specialized diagnostic tests, that often challenge diagnostic laboratories. At present, many of the commonly encountered, non-syndromic platelet disorders do not have a defined molecular cause. Nonetheless, significant progress has been made over the past few decades to improve the diagnostic evaluation of inherited platelet disorders, from the assessment of the bleeding history to improved standardization of light transmission aggregometry, which remains a "gold standard" test of platelet function. Some platelet disorder test findings are highly predictive of a bleeding disorder and some show association to symptoms of prolonged bleeding, surgical bleeding, and wound healing problems. Multiple assays can be required to diagnose common and rare platelet disorders, each requiring control of preanalytical, analytical, and post-analytical variables. The laboratory investigations of platelet disorders include evaluations of platelet counts, size, and morphology by light microscopy; assessments for aggregation defects; tests for dense granule deficiency; analyses of granule constituents and their release; platelet protein analysis by immunofluorescent staining or flow cytometry; tests of platelet procoagulant function; evaluations of platelet ultrastructure; high-throughput sequencing and other molecular diagnostic tests. The focus of this article is to review current methods for the diagnostic assessment of platelet function, with a focus on contemporary, best diagnostic laboratory practices, and relationships between clinical and laboratory findings.

Ex vivo anticoagulants affect human blood platelet biomechanics with implications for high-throughput functional mechanophenotyping

Inherited platelet disorders affecting the human platelet cytoskeleton result in increased bleeding risk. However, deciphering their impact on cytoskeleton-dependent intrinsic biomechanics of platelets remains challenging and represents an unmet need from a diagnostic and prognostic perspective. It is currently unclear whether ex vivo anticoagulants used during collection of peripheral blood impact the mechanophenotype of cellular components of blood. Using unbiased, high-throughput functional mechanophenotyping of single human platelets by real-time deformability cytometry, we found that ex vivo anticoagulants are a critical pre-analytical variable that differentially influences platelet deformation, their size, and functional response to agonists by altering the cytoskeleton. We applied our findings to characterize the functional mechanophenotype of platelets from a patient with Myosin Heavy Chain 9 (MYH9) related macrothrombocytopenia. Our data suggest that platelets from MYH9 p.E1841K mutation in humans affecting platelet non-muscle myosin heavy chain IIa (NMMHC-IIA) are biomechanically less deformable in comparison to platelets from healthy individuals.

Sachs et al. examine the effects of different ex vivo anticoagulants on the biomechanical and functional properties of single platelets using high-throughput real-time fluorescence and deformability cytometry (RT-FDC). Their results demonstrate that the choice of ex vivo anticoagulant may strongly impact the outcomes of mechanophenotyping.

Whole blood platelet impedance aggregometry with the ROTEM platelet device: comparison of 2 anticoagulants and storage times for the establishment of canine reference intervals

The ROTEM platelet device, a point-of-care whole blood platelet impedance aggregometer, is an add-on to the rotational thromboelastometry ROTEM delta device. The latter has been validated in dogs. We examined whether canine whole blood is suited for analysis with the ROTEM platelet device using adenosine-5'-diphosphate (ADP) and arachidonic acid (ARA) as agonists for platelet activation, and if there are significant differences between sample storage times and anticoagulants used. Subsequently, we determined canine reference intervals (RIs) for the ROTEM platelet device for ADP and ARA. In a pilot study, we examined whole blood from 7 dogs after 15-min and 60-min storage of lithium-heparinized samples and 40-min and 80-min storage of hirudinized samples. Statistical analysis showed no significant differences between ROTEM platelet device results for both ADP and ARA in lithium-heparin and hirudin anticoagulated canine whole blood. Lithium-heparinized blood samples analyzed after 15-min storage had the lowest coefficient of variation. RIs were determined for heparinized whole blood samples from 49 dogs after 15 min of storage.

Influence of different methods and anticoagulants on platelet parameter measurement

Platelets are the smallest and perhaps the most versatile components of human blood. Besides their role in coagulation and the maintenance of vascular integrity, they are involved in many physiological processes, ranging from immune response and leukocyte recruitment to the production of antimicrobial peptides and immune-suppressive factors like TGF-β. These versatile abilities make platelets interesting for researchers from different disciplines. However, beside profound investigation into platelets’ physiological role, there is a need for correct, standardized and thus reproducible quantification of platelet parameters. Mean platelet volume (MPV) is a widespread prognostic marker for several conditions, such as, acute coronary syndrome, chronic kidney disease and liver cirrhosis. Platelet activation is regarded as a marker for inflammatory processes, for example in autoimmune diseases such as type-1 diabetes, systemic lupus erythematosus and rheumatoid arthritis. The monitoring of platelet function is relevant for patients receiving antiplatelet medication. Platelet parameter measurement is affected by the choice of in vitro anticoagulant, the measurement technology and the time delay after sampling. This review focuses on the pre-analytical variability that arises as a result of the use of different in vitro anticoagulants and analyzer technologies when determining platelet parameters, since, even approximately 180 years after the discovery of platelets, there is still no standardized procedure.

Effects of Time-Interval since Blood Draw and of Anticoagulation on Platelet Testing (Count, Indices and Impedance Aggregometry): A Systematic Study with Blood from Healthy Volunteers

Platelet count, indices (mean volume, young-immature platelet fraction) and aggregation are widely used laboratory parameters to investigate primary hemostasis. We performed a systematic, thorough evaluation of the influence of the time-interval since blood draw from 20 healthy individuals and of the anticoagulation of collected blood on such parameters. Blood was anticoagulated with citrate, K₂-ethylenediaminetetraacetic acid (EDTA) and hirudin and analyzed 5, 30, 60, 120 and 180 min after blood draw. Multiple electrode aggregometry (MEA) was performed with either hirudin (half-diluted with NaCl) or citrate samples (half-diluted with NaCl or CaCl₂ 3 mM). Platelet count and indices (Sysmex XN-20) were rather stable over time with EDTA blood. MEA results were lower with citrate blood than with hirudin blood; supplementation with calcium was partially compensatory. MEA results were also lower when performed less than 30 or more than 120 min after blood draw. Platelet clumping, quantitatively estimated with microscope examination of blood smears, was more important in hirudin blood than citrate or EDTA blood and could explain some of the differences observed between preanalytical variables. The results stress once more the importance of preanalytical variables in hemostasis laboratory testing. Decision thresholds based on those tests are only applicable within specific preanalytical conditions.

The Effect of Mushroom Extracts on Human Platelet and Blood Coagulation: In vitro Screening of Eight Edible Species

Cardiovascular diseases remain the leading global cause of mortality indicating the need to identify all possible factors reducing primary and secondary risk. This study screened the in vitro antiplatelet and anticoagulant activities of hot water extracts of eight edible mushroom species (Agaricus bisporus, Auricularia auricularia-judae, Coprinuscomatus, Ganodermalucidum, Hericium erinaceus, Lentinulaedodes, Pleurotuseryngii, and Pleurotusostreatus) increasingly cultivated for human consumption, and compared them to those evoked by acetylsalicylic acid (ASA). The antioxidant capacity and concentration of polysaccharides, phenolic compounds, organic acids, ergosterol, macro elements, and trace elements were also characterized. The most promising antiplatelet effect was exhibited by A. auricularia-judae and P. eryngii extracts as demonstrated by the highest rate of inhibition of adenosine-5′-diphosphate (ADP)-induced and arachidonic acid (AA)-induced aggregation. The response to both extracts exceeded the one evoked by 140 µmol/L of ASA in the ADP test and was comparable to it in the case of the AA test. Such a dual effect was also observed for G. lucidum extract, even though it was proven to be cytotoxic in platelets and leukocytes. The extract of P. ostreatus revealed an additive effect on AA-induced platelet aggregation. None of the mushroom extracts altered the monitored coagulation parameters (prothrombin time, prothrombin ratio, and International Normalized Ratio). The effect of mushroom extracts on platelet function was positively related to their antioxidative properties and concentration of polysaccharides and ergosterol, and inversely related to zinc concentration. The study suggests that selected mushrooms may exert favorable antiplatelet effects, highlighting the need for further experimental and clinical research in this regard.

Platelet function in lung cancer patients undergoing lobectomy

A growing interest concerns arterial thromboembolic disease in cancer patients. As platelets may be key players in this process, investigation of platelet aggregation in cancer patients is of importance. We aimed to investigate platelet aggregation in patients with lung cancer prior to surgery and during video-assisted thoracoscopic surgery (VATS) lobectomy compared with lobectomy performed through a thoracotomy. We included 93 patients (VATS + low molecular weight heparin (LMWH), n = 32; VATS no LMWH, n = 31; thoracotomy + LMWH, n = 30). Data obtained from 121 healthy individuals were used for comparison prior to surgery. Platelet aggregation was analysed by impedance aggregometry using adenosine diphosphate 6.5 μM (ADPtest) and collagen 3.2 μg/mL (COLtest) as agonists. Prior to surgery, platelet aggregation was significantly increased in both VATS-patients (ADPtest, p < .0001; COLtest, p = .0002) and patients undergoing thoracotomy (ADPtest, p < .0001; COLtest, p < .0001) compared with healthy individuals. Platelet aggregation did not differ between VATS-patients and thoracotomy patients prior to surgery (p-values >.11). At the first postoperative day, VATS-patients demonstrated significantly higher collagen-induced platelet aggregation than preoperatively (p = .001), but the increase in platelet aggregation did not differ significantly between VATS and thoracotomy patients (p-values ≥.24). At the second postoperative day, platelet aggregation was significantly reduced in thoracotomy patients compared with the preoperative level (ADPtest, p = .002; COLtest, p = .05). In conclusion, platelet aggregation was significantly increased in patients with primary lung cancer prior to surgery compared with healthy individuals. At the first postoperative day, platelet aggregation was significantly higher than the preoperative level in VATS-patients; however, this increase did not differ between patient groups.

Multiple electrode aggregometry and thromboelastography in thrombocytopenic patients with haematological malignancies

BACKGROUND

In thrombocytopenic patients better assessment of bleeding risk than that provided by platelet count alone is required. Multiplate® aggregometry and thromboelastography (TEG) could be used, but information on their role in such patients is limited. The primary aim of this study was to investigate the feasibility of Multiplate® analyses in patients with haematological malignancies. A secondary aim was to explore whether a multiple logistic regression model combining Multiplate®, TEG, clinical and laboratory variables was associated with risk of bleeding.

MATERIALS AND METHODS

This was an exploratory, prospective observational study of thrombocytopenic patients with haematological malignancies. Total platelet count (TPC), white blood cell count, C-reactive protein (CRP) level, temperature and bleeding status were recorded daily. TEG and Multiplate® analyses with four agonists were performed on weekdays.

RESULTS

Ten patients were enrolled into the study. The median number of days in a study period was 21. Bleeding was observed on 64 of 298 study days. TPC <20×109/L and <10×109/L occurred on 119 and 25 days, respectively. When TPC was <33×109/L, many samples showed no aggregation, regardless of bleeding status. Despite this, the odds of World Health Organization (WHO) grade 2 bleeding decreased significantly as aggregation increased and Multiplate® had a negative predictive value (NPV) of 96% and a positive predictive value (PPV) of 19% for significant bleeding. In the multiple logistic regression model collagen-activated Multiplate® aggregation, TEG angle, TEG reaction time and CRP significantly affected the odds of WHO grade 2 bleeding. The combined model had a NPV of 99% and a PPV of 19%.

DISCUSSION

Our findings suggest that the markers of platelet function and haemostasis provided by Multiplate® aggregometry and TEG may add information to support prediction of bleeding, although platelet count still remains the most accessible analysis for routine testing.

Whole blood platelet aggregation determined by the ROTEM platelet equipment; reference intervals and stability

Point of care testing of residual effect of antiplatelet therapy in trauma patients or during major surgery may result in improved clinical management of significant bleeding. We included 121 healthy individuals (57 females and 64 males, aged 22-65 years) in order to establish reference intervals for platelet aggregation induced by adenosine diphosphate (ADPTEM, 10 µM), arachidonic acid (ARATEM, 0.42 mM) and thrombin activating peptide (TRAPTEM, 36 µM) employing the ROTEM platelet module. Further, the impact of citrate (3.2%) and hirudin (>15 µg/ml) as anticoagulants was evaluated. Finally, we investigated assay stability (15, 30, 60, and 120 min after blood sampling) (n = 8) and between-day variation (n = 5). We report reference intervals for 121 healthy individuals and reference intervals by gender. We observed significantly higher platelet aggregation in females than in males (all P-values < 0.05). No correlation between age and platelet aggregation was observed, except for the parameter TRAPTEM amplitude (A6), in which a decline in A6 was observed with increasing age (P = 0.03). We observed significantly lower levels of platelet aggregation in citrate tubes than in hirudin tubes (all P-values < 0.05), except from TRAPTEM maximum slope, where no significant difference was observed (P = 0.40).The stability was acceptable (≤20% deviation) for up to 120 min for ARATEM in citrate tubes, and up to 60 min for the ADPTEM and TRAPTEM assays in citrate tubes. In hirudin tubes we found ADPTEM and ARATEM assays to be stable for 60 min, while the stability of TRAPTEM in hirudin tubes was found to be stable for 30 min. Using citrate tubes, the between-day variation (mean coefficient of variation, CV) was 19-20% for ADPTEM, 19-26% for TRAPTEM, and 10% for ARATEM, whereas the mean CV was 11-13% for all three assays in hirudin tubes.In conclusion, we established combined and gender-specific reference intervals for three platelet aggregation assays in both citrate- and hirudin tubes. In citrate tubes, the stability of the ROTEM platelet assays was 60-120 min, while the stability in hirudin tubes was 30-60 min. The between-day variation was lowest for samples obtained in hirudin tubes.

On-treatment platelet reactivity in peripheral and coronary blood in patients undergoing primary PCI for ST-segment elevation myocardial infarction (STEMI)

Dual antiplatelet therapy is recommended in patients undergoing primary percutaneous coronary intervention (p-PCI) for ST-segment elevation myocardial infarction (STEMI). Pre-analytical variables may influence platelet function analysis results. Our aim was to evaluate the on-treatment platelet reactivity in peripheral artery vs coronary blood in patients with STEMI. We enrolled one hundred and nine patients who consecutively underwent p-PCI at Cardiology Unit of Padua University Hospital between June 2014 and June 2015. Before the procedure, all patients received intravenous aspirin 250 mg and either of the thienopyridines; clopidogrel 600 mg, prasugrel 60 mg or ticagrelor 180 mg. ASPI-test and ADP-test using multiple electrode aggregometry (MEA) were performed in samples collected from both a peripheral artery and the culprit coronary artery. 'Low responders' were patients with an ASPI-test or ADP-test value greater than or equal to a pre-established normal range. No significant differences were observed in ASPI-test values between peripheral (19 (median) [3-49 (10-90 percentiles)] U) vs coronary (12 [1-40] U, p = .06) blood and in ADP-test (40 [14-82] U vs 33 [7-79] U, p =.68) blood. In peripheral blood, fifteen (14%) patients were 'low aspirin' and forty-one (38%) 'low thienopyridines' responders. The prevalence of 'low clopidogrel' responders was higher (45%) than prasugrel (36%) and ticagrelor (33%). Similar results were observed in coronary blood. In patients undergoing p-PCI for STEMI, MEA platelet function observed in coronary arteries was consistent with peripheral artery blood's independently of the antiplatelet drug used. The clinical significance of peripheral and coronary on-aspirin/thienopyridines platelet reactivity needs further clarification.

Standardization and reference ranges for whole blood platelet function measurements using a flow cytometric platelet activation test

Introduction

Platelet function testing with flow cytometry has additional value to existing platelet function testing for diagnosing bleeding disorders, monitoring anti-platelet therapy, transfusion medicine and prediction of thrombosis. The major challenge is to use this technique as a diagnostic test. The aim of this study is to standardize preparation, optimization and validation of the test kit and to determine reference values in a population of 129 healthy individuals.

Methods

Platelet function tests with 3 agonists and antibodies against P-selectin, activated αIIbβ3 and glycoprotein Ib (GPIb), were prepared and stored at -20°C until used. Diluted whole blood was added and platelet activation was quantified by the density of activation markers, using flow cytometry. Anti-mouse Ig κ particles were included to validate stability of the test and to standardize results. Reference intervals were determined.

Results

Blood stored at room temperature (RT) for up to 4h after blood donation and preheated/tested at 37°C resulted in stable results (%CV<10%), in contrast to measuring at RT. The intra-assay %CV was <5%. Incubation of anti-mouse Ig κ particles with antibodies stored for up to 12 months proved to give a stable fluorescence. The inter-individual variation measured in the 129 individuals varied between 23% and 37% for P-selectin expression and αIIbβ3 activation, respectively.

Conclusions

The current study contributes to the translation of flow cytometry based platelet function testing from a scientific tool to a diagnostic test. Platelet function measurements, using prepared and stored platelet activation kits, are reproducible if executed at 37°C. The reference ranges can be validated in clinical laboratories and ongoing studies are investigating if reduced platelet reactivity in patients with bleeding complications can be detected.

Hirudin anticoagulation allows more rapid determination of P2Y12 inhibition by the VerifyNow P2Y12 assay

VerifyNow (VN) P2Y12 is a point-of-care assay used to assess response to P2Y12 inhibitors. Sodium citrate (citrate) is the standard anticoagulant used for this assay but requires a pre-incubation period. Hirudin is an alternative anticoagulant for platelet function studies that maintains physiological divalent cation levels. We investigated whether hirudin anticoagulation might allow more rapid testing of P2Y12 inhibition at the time of percutaneous coronary intervention (PCI). Blood was collected from the arterial sheath of aspirin-treated patients undergoing elective, urgent or emergency coronary angiography ± PCI and aliquots were anticoagulated with either citrate or hirudin. For each anticoagulant, VN P2Y12 was performed both immediately and after 20 minutes. A total of 98 patients were included in this study following pre-treatment with clopidogrel (n = 88), prasugrel (n = 6) or no P2Y12 inhibitor (n = 4). PRU with hirudin immediately (PRU_H_Imm) and PRU with citrate 20 minutes post sampling (PRU_C_20) were very strongly correlated (R = 0.95) though PRU_H_Imm tended to be lower than PRU_C_20 so that optimal correlation was estimated by the equation PRU_H_Imm = 0.95 x PRU_C_20 (p < 0.001). Bland-Altman plots showed good agreement between PRU_H_Imm and (0.95 x PRU_C_20). Platelet reactivity was more stable over the studied time course with hirudin as compared to citrate. We therefore conclude that VN P2Y12 with hirudin anticoagulation can be performed more rapidly and results are strongly correlated with delayed citrate measurements. Further studies are warranted to assess the utility of this method for improving clinical outcomes in patients undergoing PCI.

Comparison of current platelet functional tests for the assessment of aspirin and clopidogrel response

The two most widely used antiplatelet drugs in the world are aspirin and clopidogrel. However, some patients on aspirin and/or clopidogrel therapy do not respond appropriately to either aspirin or clopidogrel. This phenomenon is usually called “aspirin/clopidogrel resistance”. Several platelet function tests have been used in various studies for the assessment of aspirin and clopidogrel resistance in healthy individuals and patients admitted in cardiology departments. An accurate assessment of platelet response to aspirin/clopidogrel could benefit patients by proposing tailored-antiplatelet therapy based on test results. However, there is a clear lack of standardisation of such techniques and their analytical variability may induce misinterpretation. After a quick report of the mechanisms responsible for aspirin/clopidogrel resistance, we describe the pre-analytical aspects and the analytical performances of current platelet function tests (Light-transmission aggregometry, whole-blood aggregometry, VerifyNow®, Platelet Function Analyzer®, thromboelastography, VASP assay) that are used for the assessment of aspirin/clopidogrel resistance in clinical studies. Considering the different variables that have to be taken into account with each of the platelet function tests, a particular attention should be paid when interpreting results.

Comparison of multiple electrode aggregometry with lumi-aggregometry for the diagnosis of patients with mild bleeding disorders

Essentials There is a clinical need for new technologies to measure platelet function in whole blood. Mild bleeding disorders were evaluated using multiple electrode aggregometry (MEA). MEA is insensitive at detecting patients with mild platelet function and secretion defects. More studies are required to investigate MEA in patients with a defined set of platelet disorders.

SUMMARY

Background Multiple electrode aggregometry (MEA) measures changes in electrical impedance caused by platelet aggregation in whole blood. This approach is faster, more convenient and offers the advantage over light transmission aggregometry (LTA) of assessing platelet function in whole blood and reducing preanalytical errors associated with preparation of platelet-rich plasma (PRP). Several studies indicate the utility of this method in assessing platelet inhibition in individuals taking antiplatelet agents (e.g. aspirin and clopidogrel). Objective Our current study sought to evaluate the ability of MEA in diagnosing patients with mild bleeding disorders by comparison with light transmission lumi-aggregometry (lumi-LTA). Methods Forty healthy subjects and 109 patients with a clinical diagnosis of a mild bleeding disorder were recruited into the UK Genotyping and Phenotyping of Platelets study (GAPP, ISRCTN 77951167). MEA was performed on whole blood using one or two concentrations of ADP, PAR-1 peptide, arachidonic acid and collagen. Lumi-LTA was performed in PRP using several concentrations of ADP, adrenaline, arachidonic acid, collagen, PAR-1 peptide and ristocetin. Results Of 109 patients tested, 54 (49%) patients gave abnormal responses by lumi-LTA to one or more agonists. In contrast, only 16 (15%) patients were shown to have abnormal responses to one or more agonists by MEA. Conclusions In this study we showed that MEA is less sensitive in identifying patients with abnormal platelet function relative to lumi-LTA.

Does whole blood coagulation analysis reflect developmental haemostasis?

: Developmental haemostasis has been well documented over the last 3 decades and age-dependent reference ranges have been reported for a number of plasmatic coagulation parameters. With the increasing use of whole blood point-of-care tests like rotational thromboelastometry (ROTEM) and platelet function tests, an evaluation of age-dependent changes is warranted for these tests as well. We obtained blood samples from 149 children, aged 1 day to 5.9 years, and analysed conventional plasmatic coagulation tests, including activated partial prothrombin time, prothrombin time, and fibrinogen (functional). Whole blood samples were analysed using ROTEM to assess overall coagulation capacity and Multiplate analyzer to evaluate platelet aggregation. Age-dependent changes were analysed for all variables. We found age-dependent differences in all conventional coagulation tests (all P values < 0.05), but there was no sign of developmental changes in whole blood coagulation assessment when applying ROTEM, apart from clotting time in the EXTEM assay (P < 0.03). Despite marked differences in mean platelet aggregation between age groups, data did not reach statistical significance. Citrate-anticoagulated blood showed significantly reduced platelet aggregation compared with blood anticoagulated with heparin or hirudin (all P values < 0.003). We confirmed previous developmental changes in conventional plasmatic coagulation test. However, these age-dependent changes were not displayed in whole blood monitoring using ROTEM or Multiplate analyzer. Type of anticoagulant had a significant influence on platelet aggregation across all age groups.

Evaluation of platelet function in thrombocytopenia

Whole blood aggregometry is a functional assay for determination of platelet function. Until now, whole blood aggregometry has not been considered feasible at low platelet counts. Hence, the objectives of the present study were to explore platelet function in thrombocytopenia using a novel index of impedance aggregometry adjusted for platelet count and evaluate the association to platelet function assessed by flow cytometry. Hirudin anticoagulated blood was collected from 20 healthy volunteers, 20 patients with primary immune thrombocytopenia (ITP), and 17 hematological cancer patients. Platelet function was analyzed by impedance aggregometry and by flow cytometry. Collagen, adenosine diphosphate, thrombin receptor agonist peptide-6, and ristocetin were used as agonists for both analyses. Thrombocytopenia in healthy whole blood was induced in vitro employing a recently published method. Platelet aggregation of thrombocytopenic patients was evaluated relative to the aggregation of healthy volunteers at the same platelet count. In flow cytometry, platelet function was described as expression of the platelet surface glycoproteins: bound fibrinogen, CD63, and P-selectin. Similar platelet counts were obtained in the patient groups (p = 0.69) (range: 13-129 × 10⁹/l). Aggregation adjusted for platelet count was significantly increased in ITP patients compared to healthy platelets across all agonists. The platelet aggregation was high in the 95% prediction interval, with 18 ITP patients above the prediction interval in at least two agonists. In contrast, the platelet aggregation was low in the prediction interval in cancer patients, and three cancer patients with platelet aggregation below the prediction interval in at least one agonist. ITP patients displayed increased expression of bound fibrinogen and CD63 following activation, compared with particularly cancer patients, but also compared with healthy platelets. This study demonstrated the feasibility of a novel approach to perform platelet function analyses in thrombocytopenia using impedance aggregometry adjusted for platelet count.

New-Generation Thromboelastography: Comprehensive Evaluation of Citrated and Heparinized Blood Sample Storage Effect on Clot-Forming Variables

Context.—

Thromboelastography (TEG) is a whole blood, real-time analyzer measuring the viscoelastic properties of the hemostasis process and allowing for individualized goal-directed therapy. However, routine use of TEG requires validation of sample storage effect on clot parameters.

Objectives.—

To establish the minimum time required for equilibration time and the maximum time for sample storage for all commercially available TEG tests for the new-generation TEG 6s and to determine how those times compare with the older generation TEG 5000.

Design.—

Citrated and heparinized whole blood samples obtained from 20 healthy donors were analyzed for clot parameters at multiple time points for both the TEG 6s and the TEG 5000. Samples were activated with the citrated multichannel cartridge or the platelet-mapping cartridge in the TEG 6s or with recalcified kaolin in the TEG 5000.

Results.—

All blood samples yielded TEG parameter results within reference ranges and had a tendency toward hypercoagulable profiles with increased storage time. Sample storage resulted in increased platelet inhibition with significant differences at 4 hours in the platelet-mapping cartridge (arachidonic acid percentage of inhibition, P = .002; adenosine diphosphate percentage of inhibition, P = .02).

Conclusions.—

For nonemergent cases or in a central laboratory setting, all tests provided reliable results for up to 4 hours in the citrated multichannel cartridge and for 3 hours for platelet function information in the platelet-mapping cartridge. In emergent/urgent situations in which the sample needs to be run immediately, RapidTEG and functional fibrinogen tests may be preferred.

The role of spinal thrombin through protease-activated receptor 1 in hyperalgesia after neural injury

OBJECTIVE Painful neuropathic injuries induce blood-spinal cord barrier (BSCB) breakdown, allowing pro-inflammatory serum molecules to cross the BSCB, which contributes to nociception. The goal of these studies was to determine whether the blood-borne serine protease thrombin also crosses a permeable BSCB, contributing to nociception through its activation of protease-activated receptor-1 (PAR1). METHODS A 15-minute C-7 nerve root compression, which induces BSCB breakdown and painful behaviors by Day 1, was administered in the rat (n = 10); sham operation (n = 11) and a 3-minute compression (n = 10) that does not induce sensitivity were administered as controls. At Day 1 after root compression, spinal cord tissue was co-immunolabeled for fibrin/fibrinogen, the enzymatic product of thrombin, and IgG, a serum protein, to determine whether thrombin acts in areas of BSCB breakdown. To determine whether spinal thrombin and PAR1 contribute to hyperalgesia after compression, the thrombin inhibitor hirudin and the PAR1 antagonist SCH79797, were separately administered intrathecally before compression injuries (n = 5-7 per group). Rat thrombin was also administered intrathecally with and without SCH79797 (n = 6 per group) to determine whether spinal thrombin induces hypersensitivity in naïve rats through PAR1. RESULTS Spinal fibrin(ogen) was elevated at Day 1 after root compression in regions localized to BSCB breakdown and decreased in those regions by Day 7. Blocking either spinal thrombin or PAR1 completely prevented compression-induced hyperalgesia for 7 days. Intrathecal thrombin induced transient pain that was prevented by blocking spinal PAR1 before its injection. CONCLUSIONS The findings of this study suggest a potent role for spinal thrombin and its activation of PAR1 in pain onset following neuropathic injury.

Assessment of Platelet Function in Whole Blood by Flow Cytometry

Evaluation of platelet function is important for understanding the physiology of hemostasis and thrombosis and is utilized in clinical practice to diagnose inherited and acquired platelet bleeding disorders. Flow cytometry is a powerful tool for rapid evaluation of multiple functional properties of large number of platelets in whole blood and offers many advantages over other traditional methods. Attention to pre-analytical factors is required to ensure biologically valid and robust results.

Impedance aggregometric analysis of platelet function of apheresis platelet concentrates as a function of storage time

Multiple electrode (impedance) aggregometry (MEA) allows reliable monitoring of platelet function in whole blood. The aims of the present study were to implement MEA for analyzing aggregation in platelet concentrates and to correlate results with storage time and blood gas analysis (BGA). We investigated the influence of platelet counts, calcium concentrations and agonists on platelet aggregation. Samples of apheresis concentrates up to an age of 12 days were investigated by MEA and BGA. For ASPI- and TRAPtest MEA was reproducible for a platelet count of 400 per 10^-9L and a calcium concentration of 5 mmol L^-1. Platelets at the age of 2-4 days yielded steady aggregation. Platelet concentrates exceeding the storage time for transfusion showed steady aggregation up to 10 days, but a significant decline on day 12. Weak correlation was found regarding pCO₂ and MEA as well as regarding glucose concentration and MEA. Our results indicate that MEA is applicable for evaluation of aggregation in stored apheresis concentrates. Prolonged storage seems not to be prejudicial regarding platelet aggregation. Platelet concentrates showed acceptable BGA throughout storage time. Further studies are required to evaluate the application of MEA for quality controls in platelet concentrates.

Monitoring ASA and P2Y12-specific platelet inhibition--comparison of conventional (single) and multiple electrode aggregometry

OBJECTIVE

Several platelet function test systems exist for the evaluation of the platelet inhibitory effect in patients on P2Y12 inhibitors and/or acetylsalicylic acid (ASA, aspirin) therapy. Studies comparing different available assays found only a poor correlation. The objective of the present study was to evaluate the correlation and agreement between single electrode (SEA) and multiple electrode (MEA) aggregometry.

METHODS AND RESULTS

In whole blood arachidonic acid (AA) and adenosine diphosphate (ADP)-induced platelet aggregation was measured simultaneously using SEA (Chrono-Log) and MEA (Multiplate). We analyzed a total of 226 measurements taken from 58 patients on single ASA therapy or dual antiplatelet therapy with ASA and a thienopyridine. A cut-off value for clopidogrel/prasugrel high on-treatment platelet reactivity (HPR) of > 47 units (U) was chosen for MEA testing using hirudin and > 5 Ohm for SEA with citrate anticoagulated blood samples. The respective cut-off values for ASA HPR were > 30 U for the MEA assay and > 1 Ohm for SEA testing. There was a good correlation of the prevalence of thienopyridine-HPR in both whole blood assays (Spearman rank correlation coefficient r = 0.698) and a good inter-rate accordance (Cohen's Kappa statistic κ = 0.648). For AA-induced aggregation, the correlation of the results obtained was significant (r = 0.536; p < 0.001) and detecting ASA-HPR revealed a moderate (κ = 0.482) correlation between both impedance aggregometry assays.

CONCLUSION

Platelet function testing using SEA and MEA provided both good accordance and correlation and therefore study results obtained by these two assays similarly enabled the detection of HPR of thienopyridine (and ASA) therapy.

Determinants of reduced antiplatelet effect of aspirin in patients with stable coronary artery disease

Background

Aspirin is a cornerstone in management of coronary artery disease (CAD). However, considerable variability in the antiplatelet effect of aspirin has been reported.

Aim

To investigate independent determinants of reduced antiplatelet effect of aspirin in stable CAD patients.

Methods

We performed a cross-sectional study including 900 stable, high-risk CAD patients. Among these, 795 (88%) had prior myocardial infarction, 250 (28%) had type 2 diabetes, and 170 (19%) had both. All patients received 75 mg aspirin daily as mono antiplatelet therapy. The antiplatelet effect of aspirin was assessed by measurement of platelet aggregation employing 1) multiple electrode aggregometry (MEA, Multiplate Analyzer) in whole blood anticoagulated with citrate or hirudin using arachidonic acid (AA) or collagen as agonists, and 2) VerifyNow Aspirin Assay. Compliance was assessed by measurement of serum thromboxane B₂.

Results

Platelet count, prior myocardial infarction, type 2 diabetes and body mass index were independent determinants of increased AA-induced MEA platelet aggregation in citrate and hirudin anticoagulated blood (p-values ≤ 0.045). Similar results were found with VerifyNow. Prior coronary artery bypass grafting, age, smoking (MEA, AA/citrate) and female gender (MEA, AA/hirudin) were also independent determinants of increased platelet aggregation (p-values ≤ 0.038). Compliance was confirmed by low serum thromboxane B₂ levels in all patients (median [25%;75%]: 0.97 [0.52;1.97], range 0.02-26.44 ng/ml).

Conclusion

Platelet count, prior myocardial infarction, type 2 diabetes and body mass index were independent determinants of increased platelet aggregation, indicating that these characteristics may be key factors in reduced antiplatelet effect of aspirin in stable CAD patients.

Reference range determination for whole-blood platelet aggregation using the Multiplate analyzer

OBJECTIVES

To develop reference ranges for platelet aggregation using the Multiplate analyzer (Roche Diagnostics, Mannheim, Germany) in blood anticoagulated with sodium citrate (Na-citrate), lithium heparin (Li-heparin), or hirudin.

METHODS

The study was performed at three sites on consented, healthy adults (n = 193) not taking antiplatelet medication. Platelet aggregation was evaluated in response to adenosine-5'-diphosphate, arachidonic acid, collagen, thrombin receptor activating peptide, ristocetin, and adenosine-5'-diphosphate combined with prostaglandin E1. Precision testing was conducted using healthy donors and donors taking aspirin.

RESULTS

Whole-blood platelet aggregation showed anticoagulant-dependent differences in platelet responses to all agonists. Samples collected in Na-citrate demonstrated the lowest responses to all agonists. The highest responses were obtained using Li-heparin. Precision testing revealed high variability in platelet aggregation at lower agonist doses, regardless of anticoagulant. Highest platelet response variations occurred in response to arachidonic acid in blood anticoagulated with hirudin from participants taking aspirin.

CONCLUSIONS

These data demonstrate the importance of establishing locally relevant reference ranges.

Rapid evaluation of platelet function using the Multiplate® Analyzer

Rapid evaluation of platelet function may be advantageous in the setting of surgical and interventional procedures to tailor treatment of ongoing bleeding. We investigated if platelet function testing performed with the Multiplate® Analyzer (Roche Diagnostics, Mannheim, Germany) only 5 minutes after blood sampling yields reliable test results compared to analyses performed 30 minutes after sampling as currently recommended. We included 48 patients with type II diabetes and stable coronary artery disease treated with aspirin 75 mg daily and 50 healthy individuals not taking any medications. Platelet aggregometry by the Multiplate® Analyzer was performed 5 and 30 minutes after blood sampling using arachidonic acid (1.0 mM), collagen (3.2 µg/ml) and adenosine diphosphate (ADP; 6.5 µM) as agonists. Compliance with aspirin was verified by serum thromboxane B2 measurements. Aggregation levels assessed 5 minutes after blood sampling correlated strongly with those assessed after 30 minutes irrespective of the agonist used (r-values 0.75-0.89, p values <0.0001). Aggregation levels were 4-8% lower and displayed a larger standard deviation when measured 5 minutes after sampling, compared to 30 minutes after sampling. Weak, but significant correlations were observed between platelet aggregation and platelet count (r-values = 0.28-0.39; p values <0.01). The currently recommended 30-minute standing time can be omitted, when platelet aggregation is measured using the Multiplate® Analyzer. Platelet aggregation measured 5 minutes after blood sampling correlates strongly with aggregation measured 30 minutes after sampling, but yields slightly lower aggregation levels. The Multiplate® Analyzer enables rapid on-site evaluation of platelet function.

Correlation between frequency of microembolic signals and efficacy of antiplatelet therapy in symptomatic carotid disease

BACKGROUND AND PURPOSE

The detection of microembolic signals in transcranial-Doppler monitoring is associated with a higher stroke risk. We investigated the correlation between the frequency of microembolic signals and the efficacy of the antiplatelet therapy in patients with a recent symptomatic carotid-artery stenosis.

SUBJECTS AND METHODS

Thirty-two patients (mean age: 70 years, 22 men) with a recent symptomatic carotid-artery stenosis underwent 30-minute TCD-monitoring. Twenty-three patients received acetylsalicylic-acid and 9 patients clopidogrel as antiplatelet-therapy. At the same day, the antiplatelet effect was measured with multiple-electrode-impedance aggregometry.

RESULTS

In 20 cases, the qualifying event was a stroke and in 12 cases, a TIA. Twenty-six of the patients had a >50% degree of stenosis. More than one microembolic signals were detected in 13 (40.6%) of the subjects, while multiple-electrode-impedance aggregometry revealed eight low responders (6 acetylsalicylic-acid, 2 clopidogrel). More than one microembolic signals were detected in 6 of the 8 (75.0%) patients with low response, but in only 7 of the 24 subjects (29.2%) with an effective antiplatelet treatment (sensitivity 75%, specificity 70.8%; Fisher's exact test: P = .038).

CONCLUSIONS

Our study suggests that in patients with recent symptomatic carotid-artery stenosis the detection of more than one microembolic signals might serve as a useful marker for the effectiveness of the antiplatelet treatment.

Sample transport by pneumatic tube system alters results of multiple electrode aggregometry but not rotational thromboelastometry

Pneumatic tube systems (PTS) present a convenient way for blood sample transport in medical facilities. Associated preanalytical interference in various tests is largely unknown. Implementing point-of-care coagulation management at our institution, we investigated multiple electrode aggregometry (MEA) and rotational thromboelastometry (ROTEM) after PTS transportation. Whole blood samples from patients undergoing general or trauma surgery were analysed by MEA after collection (baseline, '0 × PTS') and sent on a predefined PTS track (n = 12). MEA was repeated after samples travelled the track 4 ('4 × PTS'), 8 ('8 × PTS') and 12 times ('12 × PTS') and compared with stationary controls analysed at the same time. Samples for ROTEM (n = 6) were analysed after collection and travelling the track 12 times. An acceleration detector recorded g-forces on the PTS track. At '0 × PTS' no significant differences in MEA results were detected. Values were significantly lower for transported samples compared with controls ('4 × PTS' to '12 × PTS', p < 0.001). Furthermore, MEA results of PTS samples were significantly decreased for '4 × PTS' to '12 × PTS' compared to baseline (p < 0.001). Except for the clotting time in EXTEM PTS transport did not significantly alter results for investigated ROTEM parameters, compared with baseline and stationary controls. Acceleration detector readout revealed alternating g-forces between -6.3 and +5.9 during transport. PTS transport caused invalid results in MEA while only one ROTEM parameter was found to be affected in this study. Variable acceleration during transport provides a potential reason for platelet activation. The authors recommend sample transport by hand or the device to be placed patient-side when MEA is performed.