Whole Blood Impedance Aggregometry Research Articles

Fibrinolytic potential as a risk factor for postpartum hemorrhage.

Postpartum hemorrhage (PPH) is still the leading cause of maternal morbidity and mortality worldwide. While impaired fibrin polymerization plays a crucial role in the development and progress of PPH, recent approaches using viscoelastic measurements have failed to sensitively detect early changes in fibrinolysis in PPH. This study aimed to evaluate whether women experiencing PPH show alterations in POC-VET fibrinolytic potential during childbirth and whether fibrinolytic potential offers benefits in the prediction and treatment of PPH. Blood samples were collected at three different timepoints: T0 = hospital admission (19 h ± 18 h prepartum), T1 = 30-60 min after placental separation, and T2 = first day postpartum (19 h ± 6 h postpartum). In addition to standard laboratory tests, whole-blood impedance aggregometry (Multiplate) and viscoelastic testing (VET) were performed using the ClotPro system, which included the TPA-test lysis time, to assess the POC-VET fibrinolytic potential, and selected coagulation factors were measured. The results were correlated with blood loss and clinical outcome markers. Severe PPH was defined as a hemoglobin drop > 4g/dl and/or the occurrence of shock or the need for red blood cell transfusion. Blood samples of 217 parturient women were analyzed between June 2020 and December 2020 at Heidelberg University Women's Hospital, and 206 measurements were eligible for the final analysis. Women experiencing severe PPH showed increased fibrinolytic potential already at the time of hospital admission. When compared to non-PPH, the difference persisted 30-60 min after placental separation. A higher fibrinolytic potential was accompanied by a greater drop in fibrinogen and higher d-dimer values after placental separation. While 70% of women experiencing severe PPH showed fibrinolytic potential, 54% of those without PPH showed increased fibrinolytic potential as well. We were able to show that antepartal and peripartal fibrinolytic potential was elevated in women experiencing severe PPH. However, several women showed high fibrinolytic potential but lacked clinical signs of PPH. The findings indicate that high fibrinolytic potential is a risk factor for the development of coagulopathy, but further conditions are required to cause PPH.

Decreased Platelet Aggregation in Patients with Decompensated Liver Cirrhosis and TIPS Implantation.

Transjugular intrahepatic portosystemic shunt (TIPS) implantation is an effective treatment of portal hypertension in patients with decompensated liver cirrhosis. However, some patients develop TIPS thrombosis with recurrence of portal hypertension. The role of platelets in TIPS thrombosis and the necessity of antiplatelet therapy is unclear. Therefore, we aimed to study platelet function in patients with liver cirrhosis prior to and after TIPS implantation. Platelet aggregation was tested in peripheral and portal-vein blood patient samples on the day (D) of TIPS implantation (D0), D4 and D30 following the procedure (platelet count above 100 × 103/µL, aspirin starting on D5) using whole-blood impedance aggregometry (WBIA) and light transmission aggregometry (LTA). In addition, surface platelet activation markers (P-selectin, activated GPIIb/IIIa) and platelet-neutrophil complexes (PNCs) were assessed by flow cytometry. Thrombin receptor activating peptide 6 (TRAP-6), adenosine diphosphate (ADP) and arachidonic acid (AA) were used as agonists. Healthy subjects were included as controls. Agonist-induced platelet aggregation was reduced (WBIA: TRAP-6 p < 0.01, ADP p < 0.01, AA p < 0.001; LTA: TRAP-6 p = 0.13, ADP p = 0.05, AA p < 0.01) in patients (D0, n = 13) compared with healthy subjects (n = 9). While surface activation markers at baseline were negligibly low, the percentage of PNCs was higher in patients than in controls (p < 0.05). ADP-induced P-selectin expression was increased (p < 0.001), whereas TRAP-6-induced GPIIb/IIIa activation was impaired (p < 0.001) in patients versus controls. PNC formation in response to agonists was not different between groups. Results did not differ between peripheral and portal-vein blood of patients (D0, n = 11) and did not change over time (D0, D4, D30) following TIPS implantation (n = 9). In summary, patients with decompensated liver cirrhosis display in vitro platelet aggregation defects in response to various agonists. Defective aggregation persists upon TIPS implantation. Therefore, we conclude that antiplatelet treatment to prevent TIPS thrombosis is questionable.

The Effect of 4-Methylcatechol on Platelets in Familial Hypercholesterolemic Patients Treated with Lipid Apheresis and/or Proprotein Convertase Subtilisin Kexin 9 Monoclonal Antibodies.

Elevated low-density lipoprotein (LDL) cholesterol levels lead to atherosclerosis and platelet hyperaggregability, both of which are known culprits of arterial thrombosis. Normalization of LDL cholesterol in familial hypercholesterolemia (FH) is not an easy task and frequently requires specific treatment, such as regularly performed lipid apheresis and/or novel drugs such as proprotein convertase subtilisin kexin 9 monoclonal antibodies (PCSK9Ab). Moreover, a high resistance rate to the first-line antiplatelet drug acetylsalicylic acid (ASA) stimulated research of novel antiplatelet drugs. 4-methylcatechol (4-MC), a known metabolite of several dietary flavonoids, may be a suitable candidate. The aim of this study was to analyse the antiplatelet effect of 4-MC in FH patients and to compare its impact on two FH treatment modalities via whole-blood impedance aggregometry. When compared to age-matched, generally healthy controls, the antiplatelet effect of 4-MC against collagen-induced aggregation was higher in FH patients. Apheresis itself improved the effect of 4-MC on platelet aggregation and blood from patients treated with this procedure and pretreated with 4-MC had lower platelet aggregability when compared to those solely treated with PCKS9Ab. Although this study had some inherent limitations, e.g., a low number of patients and possible impact of administered drugs, it confirmed the suitability of 4-MC as a promising antiplatelet agent and also demonstrated the effect of 4-MC in patients with a genetic metabolic disease for the first time.

Plasma Concentration of Cortisol Negatively Associates with Platelet Reactivity in Older Subjects.

The interaction of platelets with steroid hormones is poorly investigated. Age is one of the factors that increase the risk of pathological platelet reactivity and thrombosis. The aim of this study was to assess whether there were associations between platelet reactivity and plasma cortisol levels in volunteers aged 60-65 years. For this purpose, impedance aggregometry in whole blood measured after arachidonic acid, collagen, or ADP stimulation was used to estimate platelet reactivity and mass spectrometry was used to measure peripheral plasma cortisol concentration. Statistically significant negative correlations were observed between cortisol concentration and platelet reactivity in response to arachidonic acid and ADP, but not to collagen. The presented results suggest for the very first time that cortisol is a new endogenous modulator of platelet reactivity in the elderly population.

Early SARS-CoV-2 infection: Platelet-neutrophil complexes and platelet function

BackgroundConflicting results have been reported on platelet activity ex vivo and responsiveness in vitro among patients with COVID-19 with or without thromboembolic complications. ObjectivesTo assess platelet reactivity in patients with moderate disease at early stages of COVID-19. MethodsWe performed a prospective, descriptive analysis of 100 consecutive patients presenting with suspected SARS-CoV-2 infection at University Medical Center Freiburg during the first or second wave of the pandemic. Following polymerase chain reaction testing and compliance with study inclusion criteria, 20 SARS-CoV-2–positive and 55 SARS-CoV-2–negative patients (serving as patient controls) were enrolled. In addition, 15 healthy subjects were included. Platelet reactivity was assessed using whole-blood impedance aggregometry and flow cytometry in response to various agonists. ResultsPlatelet aggregation was significantly impaired in the patients with COVID-19 compared with that in the patient controls or healthy subjects. The reduced platelet responsiveness in the patients with COVID-19 was associated with impaired activation of GPIIb/IIIa (αIIbβ3). In contrast, low expression of P-selectin at baseline and intact secretion upon stimulation in vitro suggest that no preactivation in vivo, leading to “exhausted” platelets, had occurred. The proportion of circulating platelet-neutrophil complexes was significantly higher in the patients with COVID-19 (mean ± SD, 41% ± 13%) than in the patient controls (18% ± 7%; 95% CI, 11.1-34.1; P = .0002) or healthy subjects (17% ± 4%; 95% CI, 13.8-33.8; P < .0001). An analysis of neutrophil adhesion receptors revealed upregulation of CD11b (α-subunit of αMβ2) and CD66b (CEACAM8) but not of CD162 (PSGL-1) in the patients with COVID-19. ConclusionDespite reduced platelet responsiveness, platelet-neutrophil complexes are increased at early stages of moderate disease. Thus, this cellular interaction may occur during COVID-19 without preceding platelet activation.

Discordance in tests used to detect inhibition of the P2Y12 receptor in patients undergoing interventional neuroradiology procedures.

Clopidogrel is an inhibitor of the P2Y12 platelet receptor but testing to demonstrate a drug effect is controversial since there are often discordant results between different tests methods. Samples from patients taking clopidogrel prior to intracranial flow-diversion procedures were tested using light transmission aggregometry (LTA), whole blood impedance aggregometry (WBIA) and the VerifyNow device (VND). Samples were classified as concordant if all test results were either responsive (inhibition) or resistant. Discordant results were separated using the VND into those with a responsive versus a resistant test result. Samples from 96 patients were studied. Concordance for all three tests was seen in 53/96 (55%) of samples, of which 41 (43%) were responsive and 12 (12%) were resistant. Discordance was observed in 43 samples (45%), 37 (28%) of which were caused by responsive VND and either a resistant WBIA or LTA and 6 (7%) of which were caused by a resistant VND but a responsive test result using either WBIA or LTA. These two discordant groups differed in both platelet count and hematocrit, but no such difference was present between the two concordant groups. Discordance in P2Y12 inhibition testing may be partly explained by sample platelet count and hematocrit.

167 Reversible VWF Inhibitor Lyses MCA Occlusion 6 Hours after Large Vessel Occlusion Stroke

INTRODUCTION: Acute ischemic stroke (AIS) is the leading cause of combined morbidity and mortality worldwide. Recombinant tissue plasminogen activator (rtPA) represents the only approved pharmacological treatment for AIS but is limited to treating those within 4.5 hours of stroke onset because of the risk of intracranial hemorrhage. Moreover, it is ineffective in treating large vessel occlusion (LVO) stroke. For this population, endovascular mechanical thrombectomy (MT) effectively recanalizes the occlusion but is limited to highly-specialized hospitals, leaving the vast majority without timely acute treatment. METHODS: Utilizing a canine embolic middle cerebral artery occlusion (eMCAO) model of LVO stroke, we assessed DTRI-031 on vessel recanalization after 6 hours of LVO stroke by digital subtraction angiography (DSA). We also measured the effect of recanalization on infarct volume (efficacy) and hemorrhage (safety) using magnetic resonance imaging (MRI). Finally, we assessed the ability of DTRI-025, an oligonucleotide that binds DTRI-031 to reverse DTRI-031 activity. RESULTS: DTRI-031 administration after 6 hours of LVO stroke resulted in &gt;TICI 2A in 62.5% and &gt;TICI 2B in 50% of canines (n = 8). Negative control group demonstrated no revascularization (n = 7). Recanalization resulted in reduced infarct volume compared to negative control (p &lt; 0.05, unpaired t-test). None of the animals that received DTRI-031 had intracranial hemorrhage on MRI. Finally, DTRI-025 completely reversed the activity of DTRI-031 within 5 minutes of administration in both whole blood impedance aggregometry (WBA) and PFA-100. CONCLUSION: DTRI-031 effectively recanalizes LVO after 6 hours of stroke onset with reduced infarct volume and no incidence of hemorrhage. DTRI-025 rapidly reverses DTRI-031. This drug/reversal agent combination represents a robust yet safe approach to treat AIS.

Abstract 45: Vwf Inhibitor Lyses Middle Cerebral Artery Occlusion After 6 Hours Of Large Vessel Occlusion Stroke

Introduction: Acute ischemic stroke (AIS) is the leading cause of combined morbidity and mortality worldwide. Recombinant tissue plasminogen activator (rtPA) is the only FDA-approved drug to treat AIS, however, it is limited to treating patients within 4.5 hours of stroke onset because of the risk of intracranial hemorrhage. This limits rtPA administration to ~6% of patients. Moreover, it poorly lyses large vessel occlusion (LVO) stroke. Endovascular mechanical thrombectomy (MT) effectively recanalizes LVO but is limited to highly specialized hospitals, leaving the majority without acute therapy. Hypothesis: We hypothesize that targeted von Willebrand Factor (VWF) inhibition by DTRI-031 will recanalize arterial thrombosis in a canine model of LVO stroke, and DTRI-031 activity will be rapidly reversed by DTRI-025, which is specifically designed to inhibit DTRI-031. Methods: Utilizing a canine embolic middle cerebral artery occlusion (eMCAO) model of LVO stroke, we assessed DTRI-031 on vessel recanalization after 6 hours of LVO stroke by digital subtraction angiography (DSA). We also measured the effect of recanalization on infarct volume (efficacy) and hemorrhage (safety) using magnetic resonance imaging (MRI). Finally, we assessed the ability of DTRI-025, an oligonucleotide that binds DTRI-031 to reverse DTRI-031 activity. Results: DTRI-031 administration after 6 hours of LVO stroke resulted in ≥TICI 2A in 62.5% and ≥TICI 2B in 50% of canines (n=8). The negative control group demonstrated no revascularization (n=7). Recanalization resulted in reduced infarct volume compared to the negative control (p&lt;0.05, unpaired t-test). None of the animals that received DTRI-031 had an intracranial hemorrhage on MRI. Finally, DTRI-025 completely reversed the activity of DTRI-031 within 5 minutes of administration in both whole blood impedance aggregometry (WBA) and PFA-100. There was no difference in heart rate, blood pressure, or temperature among the 3 groups studied. Conclusion: DTRI-031 effectively recanalizes LVO after 6 hours of stroke onset with reduced infarct volume and no incidence of hemorrhage. DTRI-025 rapidly reverses DTRI-031. This drug/reversal agent combination represents a robust yet safe approach to treat AIS.

Implementation of Whole-Blood Impedance Aggregometry for Heparin-Induced Thrombocytopenia Functional Assay and Case Discussion.

The diagnosis of heparin-induced thrombocytopenia (HIT) ideally requires a functional assay to confirm. 14C-serotonin release assay (SRA) as "gold standard" is technically challenging and unsuitable for routine use. We conducted a study to assess the performance of whole-blood impedance aggregometry (WBIA) as a simple and rapid HIT functional assay. Platelet factor 4 (PF4)/immunoglobulin G (IgG) antibody, WBIA, and SRA were tested on 70 patients suspected of having HIT. Patients with a 4Ts score of 4 or more, positive PF4/IgG, and positive SRA were considered HIT positive; others were designated HIT negative. WBIA had 85.7% (6/7) sensitivity and 98.4% (61/62) specificity, which were not statistically different compared with SRA. Sixty-two of 70 patients had concordant results (five positive and 57 negative) by both WBIA and SRA. Eight discordant cases revealed the importance of recognizing donor effect, interferences, and the presence of heparin-independent or non-heparin-dependent antibodies in functional assays. Implementation of WBIA could facilitate timely diagnosis and management of HIT.

Evaluation of platelet function in essential thrombocythemia under different analytical conditions

Background. Studies of platelet aggregation (PA) in essential thrombocythemia (ET) reported contrasting results, likely due to differences in analytical conditions.Objective. We investigated platelet aggregation using different techniques and analytical conditions.Patients and Methods. PA was studied by light-transmission aggregometry (LTA) in platelet-rich plasma (PRP) and impedance aggregometry in PRP and whole blood (WB). ADP, collagen, thrombin receptor activating peptide (TRAP-14) and adrenaline were used as agonists. Since ET patients (n = 41) were on treatment with aspirin (100 mg/d), healthy controls (n = 29) were given aspirin (100 mg/d) for 5 days before testing: therefore, thromboxane A2-independent PA was tested in all subjects. Blood samples were collected in citrate (C) [low Ca2+] or lepirudin (L) [physiological Ca2+]; platelet count was adjusted to 250 x 109/L in a set of C-PRP (adjusted C-PRP) and left unmodified in the other samples.Results. Results of PA in 17 ET patients who were poor responders to aspirin (high serum thromboxane B2 levels) were not included in the analysis. With LTA, PA in ET was lower than in controls in adjusted C-PRP and normal in native C-PRP and L-PRP. With impedance aggregometry, PA in L-PRP and L-WB tended to be higher in ET than in controls. Platelet serotonin and ADP contents were reduced in ET. The percentages of circulating platelets expressing P-selectin and platelet-leukocyte hetero-aggregates were higher in ET.Conclusions. Analytical conditions dramatically affect in vitro PA of ET patients, which appears defective under the least physiological conditions and normal/supranormal under conditions that are closer to the physiological.

Prevalence of high on-treatment platelet reactivity in patients with chronic kidney disease treated with acetylsalicylic acid for stroke prevention.

Introduction Chronic kidney disease (CKD) is one of risk factors for stroke and may be associated with impaired platelet reactivity. Objectives The aim of the study was to evaluate platelet reactivity in patients with CKD treated with acetylsalicylic acid (ASA), using 2 different laboratory methods. Moreover, we searched for factors responsible for the phenomenon of high on-treatment platelet reactivity (HOPR). Patients and methods A total of 108 patients with CKD and 41 controls without CKD using ASA were enrolled in the study. Platelet function was assessed by impedance aggregometry in whole blood, using a multi-channel platelet function analyzer (Multiplate®; ASPItest). Urinary 11-dehydrotromboxane levels were measured by the AspirinWorks® test. Results No significant differences were observed in the prevalence of HOPR between patients with and without CKD. Patients with CKD and HOPR measured by ASPItest had higher creatinine levels (P = 0.05) and were younger (P <0.01) than patients with CKD without HOPR, while patients with CKD and HOPR measured by AspirinWorks® had lower red blood cell count (P = 0.05), hemoglobin (P = 0.05), hematocrit (P = 0.05), and high-density lipoprotein levels (P = 0.05). All patients with HOPR had higher C-reactive protein levels (P <0.05) (AspirinWorks®) and white blood cells (P <0.05) (ASPItest). Conclusions The applied methods allowed to detect HOPR in more than one third of CKD patients taking ASA for stroke prevention. The compatibility of both methods for HOPR assessment was confirmed. The study revealed several potential risk factors for HOPR in CKD, including younger age, higher levels of inflammatory markers, dyslipidemia, and lower hematocrit and hemoglobin levels.

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.

Microbiota-dependent metabolite and cardiovascular disease marker trimethylamine-N-oxide (TMAO) is associated with monocyte activation but not platelet function in untreated HIV infection

BackgroundHIV infection is associated with increased risk of cardiovascular disease beyond that explained by traditional risk factors. Altered gut microbiota, microbial translocation, and immune activation have been proposed as potential triggers. The microbiota-dependent metabolite trimethylamine-N-oxide (TMAO) predicts myocardial infarction (MI) in the general population and has recently been shown to induce platelet hyperreactivity. In the present study, we investigated if TMAO was associated with platelet function, microbial translocation, and immune activation in both untreated and combination anti-retroviral therapy (cART) HIV infection.MethodsTMAO and the pre-cursors betaine, choline, and carnitine were quantified by mass-spectrometry in plasma samples from a previously established cross-sectional cohort of 50 untreated and 50 cART treated HIV-infected individuals. Whole-blood impedance aggregometry, C-reactive protein, sCD14, and lipopolysaccharide were assessed as measures of platelet function, inflammation, monocyte activation, and microbial translocation, respectively.ResultsTMAO was not associated with platelet aggregation response after stimulation with four different agonists, or with overall hypo- or hyperreactivity in untreated or treated HIV-infected individuals. In contrast, sCD14 a marker of both monocyte activation and microbial translocation was independently associated with TMAO in untreated HIV-infection (R = 0.381, P = 0.008). Lower levels of carnitine [32.2 (28.4–36.8) vs. 38.2 (33.6–42.0), P = 0.001] and betaine [33.1 (27.3–43.4) vs.37.4 (31.5–48.7, P = 0.02], but similar TMAO levels [3.8 (2.3–6.1), vs. 2.9 μM (1.9–4.8) P = 0.15] were found in cART treated compared to untreated HIV-infected individuals, resulting in higher ratios of TMAO/carnitine [0.12 (0.07–0.20) vs. 0.08 (0.05–0.11), P = 0.02] and TMAO/betaine [0.11 (0.07–0.17) vs. 0.08 (0.05–0.13), P 0.02].ConclusionsIn contrast to recent studies in HIV-uninfected populations, the present study found no evidence of TMAO-induced platelet hyperreactivity in HIV infected individuals. Microbial translocation and monocyte activation may affect TMAO levels in untreated individuals. Furthermore, the elevated ratios of TMAO/betaine and TMAO/carnitine in cART-treated individuals could possibly suggest a role of cART in TMAO metabolism.

Establishment of reference ranges and evaluation of in vitro concentration-dependent platelet inhibition by acetylsalicylic acid for multiple electrode impedance aggregometry in healthydogs.

Acetylsalicylic acid (ASA, aspirin) is an antiplatelet medication used for prevention of thromboembolism. Effects of ASA appear to vary widely between dogs, but the underlying mechanisms are not understood. The Multiplate analyzer is a newer form of whole-blood impedance aggregometry recently validated for use in healthy dogs. A method utilizing this instrument to measure ASA effects on platelet function has not been established. The goals of this study were to establish reference ranges for the Multiplate in healthy dogs and secondly, to develop a technique to determine the in vitro concentration of ASA needed to cause 50% inhibition of platelet aggregation (IC50). Reference ranges established from 40 dogs at multiple test times for three agonists were consistent with previously published values. In vitro IC50 values were calculated using the sigmoid Emax model in 20 healthy dogs on two occasions to determine individual repeatability. Calculated in vitro IC50 demonstrated four ASA response groups: responder (n=16), poor responder (n=1), variable responder (n=2), and nonresponder (n=1). Multiplate within-assay variability was <10% for area under the curve (AUC), and between-assay baseline AUC variability was <15%. The described technique allowed for determination of an in vitro IC50 for ASA in dogs using a multiple electrode impedance aggregometer.

Early platelet recovery following cardiac surgery with cardiopulmonary bypass

Coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) is frequently associated with low platelet count (PC) and disturbed platelet function (PF). While PC is easy to measure, PF is more difficult to assess. Moreover, the time-related platelet dysfunction and recovery after CPB is not fully elucidated. Platelet dysfunction could lead to bleeding but also to coronary graft failure. Laboratory tests could provide more insights into PF after CABG. The aim of the current study was to investigate the time-related PF induced by CPB. Blood samples of 20 patients with a preoperative PC of more than 250 × 109/L were collected before incision, after weaning from CPB, and 24 h postoperative. Platelet contribution to coagulation was quantified by PLTEM (calculated by means of EXTEM and FIBTEM results). PF was assessed by multiple electrode impedance aggregometry (MEIA) in whole blood and by light transmission aggregometry (LTA) in platelet-rich plasma after stimulation with arachidonic acid (AA), adenosine diphosphate, collagen, and thrombin-receptor-activating peptide. LTA and MEIA analysis demonstrated significant platelet dysfunction after CPB, with partial recovery within 24 h after surgery. AA-induced platelet aggregation increased to higher levels within 24 h after surgery compared to baseline values as measured by LTA. PLTEM maximum clot firmness remained unchanged throughout the study. Correlation analyses revealed that MEIA and rotational thromboelastometry (ROTEM), but not LTA, were dependent on PC and hematocrit. No correlations were found between LTA, MEIA, ROTEM, PC, and clinical outcome parameters. Our results demonstrate a reversible platelet dysfunction recovering within 24 h after CPB. Interestingly, AA-induced platelet aggregation increases to higher levels during the first 24 h postoperatively, which might be important for early initiation of antiplatelet therapy after CABG. MEIA as POC test is able to detect platelet dysfunction during cardiac surgery with a PC of ≥150 × 109/L.

Platelet Adhesion and Thrombus Formation in Whole Blood at Arterial Shear Rate at the End of Pregnancy.

Platelet reactivity has not been evaluated in integrated functional testing during normal pregnancy. Here, we analysed platelet functions under arterial shear rate in comparison with static conditions. Thirty pregnant women with uncomplicated pregnancies and 30 healthy non-pregnant women were enrolled in this study. Platelet adhesion to collagen and fibrinogen and subsequent thrombus formation were measured at arterial shear rate in whole blood using a microfluidic and imaging system. Standard light transmission aggregometry, flow cytometry of activation markers in washed platelets and impedance aggregometry in whole blood were also used to assess platelet responsiveness in static conditions. Compared to non-pregnant controls, thrombus formation on collagen fibres and firm platelet adhesion on fibrinogen under arterial shear rate were significantly reduced in pregnant women. Platelet aggregometry assays in suspension showed a slight increase in platelet reactivity in pregnant women. While platelet aggregometry and platelet activation markers in static conditions show little changes in platelet reactivity, monitoring of platelet adhesion and thrombus growth on collagen or fibrinogen under flow condition in whole blood indicates a significant decrease in pregnant women compared to controls. This decrease might contribute to counteract a hypercoagulable state and to reduce the risk of arterial thrombosis.

Haemostatic function and biomarkers of endothelial damage before and after RBC transfusion in patients with haematologic disease.

Transfusion of red blood cells (RBC) is beneficial for the patient but can also be harmful, as randomized trials have demonstrated increased infection rates, bleeding and mortality. The study aim was to investigate the response of the vascular system (the haemostatic function and the endothelium) to RBC transfusion. Blood was sampled from patients with various transfusion-dependent haematologic diseases before 1 and 24 h after RBC transfusion. Primary and secondary haemostasis was evaluated by whole-blood impedance aggregometry (Multiplate) and by thromboelastography (TEG). Samples were analysed by ELISA for biomarkers reflecting endothelial activation and damage (sICAM-1, syndecan-1, sThrombomodulin (sTM), sVE-Cadherin), platelet activation (sCD40L) and inflammation (hsCRP). A total of 58 patients were enrolled in the study. Median age was 71 years. Compared to before transfusion, patients had slightly reduced coagulability 1 h after RBC transfusion, assessed by TEG. However, transfusion of older RBC products (>14 days) was associated with increased coagulability (all P < 0·05). The level of syndecan-1 increased slightly 24 h after transfusion (median 12·4 (IQR 9-23) vs. 13·2 (9-25) ng/ml, P < 0·01), indicating increased glycocalyx degradation. Overall, RBC transfusion was associated with reduced coagulability and endothelial glycocalyx degradation. Transfusion of older RBCs was however associated with increased coagulability. The changes observed were small to moderate and the clinical relevance of these findings should be investigated in larger studies.

Dual antiplatelet response during PCI: VerifyNow P2Y12 predicts myocardial necrosis and thromboxane B2 generation confirms wide variation in aspirin response

IntroductionThere remains concern that the antiplatelet effects of aspirin and clopidogrel vary between patients and poor responders may be at increased risk of adverse events. However, the optimal method of measuring aspirin and/or clopidogrel response remains unresolved. We compared three methods of measuring clopidogrel response recommended by a recent consensus statement for the European Society of Cardiology, and investigated a novel approach to measuring aspirin response in patients established on both aspirin and clopidogrel. In addition, we investigated whether any of these assays predict peri-procedural myocardial necrosis following percutaneous coronary intervention (PCI). MethodsA cross-section of 323 patients attending for PCI was tested for clopidogrel response using VerifyNow P2Y12, VASP Platelet Reactivity Index (VASP-PRI) and whole blood impedance aggregometry (WBPA). Aspirin response was assessed by measuring the residual ability of platelets to generate thromboxane, calculated as the difference between thromboxane B2 levels in serum and plasma, [TxB2]S-P. Peri-procedural myocardial necrosis was determined by a change in troponin I >0.2μmol/l. ResultsPatients demonstrated wide variation in response to both aspirin and clopidogrel. Correlation between VerifyNow P2Y12 and VASP-PRI was good (r=0.702, p<0.001). Correlation was moderate between WBPA and VerifyNow P2Y12 (r=0.639, p<0.001) and weak for WBPA and VASP-PRI (r=0.353, p<0.001). Only VerifyNow P2Y12 predicted peri-procedural myocardial necrosis. ConclusionsThe three methods of measuring response to clopidogrel identify different patients as poor responders. Poor response to clopidogrel assessed by VerifyNow P2Y12 predicts myocardial necrosis. Measurement of [TxB2]S-P demonstrates a wide variation in aspirin response in patients taking dual antiplatelet therapy.

Novel Uses for Platelet Function Testing in the Clinical Laboratory: Where Are We Now?

Platelet function testing (PFT),7 usually performed by techniques such as light transmission aggregometry (LTA), has traditionally been used to diagnose inherited qualitative and quantitative defects in platelet function, such as von Willebrand disease or Glanzmann thrombasthenia. With the increased use of antiplatelet agents to prevent arterial thrombosis and the interest in identifying patients at risk for thrombosis despite antiplatelet therapy, the use of PFT to monitor the response to and/or titrate antiplatelet therapy (primarily aspirin and clopidogrel) has become a hot topic. Investigators and practitioners in surgery, critical care, and trauma have also pursued other nonstandard tests of coagulation, such as viscoelastic coagulation testing, to allow more-robust prediction of patients at risk for massive bleeding during invasive procedures or after major trauma. There is considerable controversy regarding the use of PFT and viscoelastic coagulation tests to monitor response to antiplatelet therapy or to guide transfusion decisions for critically ill patients. In this Q&A article, 4 experts in platelet function give their views on both the evidence and current best practice for application of PFT in these nontraditional settings. What PFTs are used clinically in your institution? What population of patients is being tested, and what clinical decisions are made based on the results? Gilles Montalescot: We perform VerifyNow (Accumetrics), light-transmission and whole-blood impedance aggregometry and perform some flow cytometric evaluation of platelet reactivity in our research unit for clinical research only; we do not routinely test patients in the catheritization laboratory. Rarely, however, we perform testing on patients when there is a good reason to do so, e.g., assessing compliance with treatment, stent thrombosis, very high–risk patients—all of which are situations that were not evaluated in the ARCTIC (Double Randomization of a Monitoring Adjusted Antiplatelet Treatment versus a Common Antiplatelet Treatment for DES Implantation, and Interruption versus Continuation of …

Simple and accessible screening method for congenital thrombopathies using an impedance haematology counter – reply: The differences between impedance aggregometry in whole blood versus aggregometry in PRP. Is there a need for caution?

Abstract Brahimi et al. in this journal formed a hypothesis that “the platelet count is underestimated, by an automated cell counter, each time platelet aggregates are present in the sample tube.” The addition of a platelet agonist to a stimulated sample tube will lead to the formation of platelet aggregates and hence to a drop in the platelet count. In the case of a hereditary platelet dysfunction, platelet aggregates cannot be formed upon addition of a platelet agonist and the platelet count will remain unchanged. The authors propose a hypothesis to develop “a more accessible screening technique for these hereditary platelet dysfunctions.” In our reply, we critically evaluate this screening method and focus on the importance of the differences between impedance aggregometry in whole blood versus aggregometry in platelet-rich plasma.