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PubMed1984

Correlation between prolonged bleeding time and depletion of platelet dense granule ADP in patients with myelodysplastic and myeloproliferative disorders.

Nine patients with myelodysplasia or myeloproliferative syndrome were studied with respect to platelet count and volume, 51Cr and 14C-serotonin platelet kinetics, bleeding time, and platelet dense and alpha-granule contents. Platelet counts ranged from 45,000 to 293,000 platelets/microliters. The bleeding time was significantly longer (greater than 4 minutes) than the predicted value in seven of nine patients. All patients had significant dense granule storage pool depletion (thrombin-releasable ADP was 0.59 +/- 0.30 vs. 2.41 +/- 0.20 mumol per 10(11) platelets in patients compared with normal volunteers; total platelet ADP was 0.97 +/- 0.29 vs. 2.72 +/- 0.15, and total platelet ATP/ADP was 4.77 +/- 1.89 vs. 1.65 +/- 0.11). The prolongation in bleeding time correlated inversely with thrombin-releasable ADP (r = -0.637, p less than 0.01) and with total ADP (r = -0.832, p less than 0.005), and directly with the ATP/ADP ratio (r = 0.781, p less than 0.005). When autologous platelets were doubly labeled with 14C-serotonin and 51Cr to test for loss of dense granule contents, marked preferential shortening of the 14C-serotonin platelet disappearance curve with relation to 51Cr platelet survival was observed in five of the six patients (six normal participants uniformly showed 14C-serotonin platelet disappearance patterns that were 15% to 20% longer than 51Cr platelet survivals). Reduction in alpha-granule contents was less striking and occurred less frequently than dense granule depletion (two of nine values were significantly reduced for platelet factor 4 content, whereas all patients had significantly reduced dense granule ADP levels). Mean plasma levels of both platelet factor 4 and beta-thromboglobulin were elevated in patients compared with normal participants (4.1 +/- 3.2 and 26.6 +/- 12.3 vs. 1.8 +/- 1.0 and 6.0 +/- 3.6 ng/ml; p less than 0.01 and p less than 0.01, respectively). Two patients had elevated urinary platelet factor 4. There was no correlation between platelet factor 4 content and thrombin-releasable platelet ADP levels (r = 0.167, p greater than 0.1). These patients had acquired storage pool deficiency of platelet dense granule ADP that correlated directly with platelet dysfunction, as measured by prolongation of bleeding time. The reduction in dense granule constituents appears to be the consequence of an ongoing loss of dense granule contents from circulating platelets.

Adenosine Diphosphate↗
PubMed1999

Familial dominant thrombocytopenia: clinical, biologic, and molecular studies.

Inherited thrombocytopenias are a heterogenous group of disorders. Different criteria have been suggested to classify the forms, such as the inheritance mechanism and the platelet volume as well as the number and morphology of megakaryocytes. However, the classification is often descriptive, and the precise mechanism of thrombocytopenia still remains unknown. We describe the clinical, biologic, and molecular findings of an autosomal dominant thrombocytopenia in a large family. The 17 patients had normocellular bone marrow and normal platelet volume. Platelets also showed a normal aggregation test and normal response to ADP and thrombopoietin (TPO). In the affected subjects, the mean +/- SD levels of platelet count and plasma TPO were 62+/-25 and 258+/-151, respectively. Comparative analysis showed that the patients with platelet count <70000 had higher plasma TPO concentration. The data are consistent with a mild clinical form of the disease associated with only a few episodes of bleeding. To exclude the possible role of TPO and its receptor c-mpl in the etiology of this condition, linkage analysis was performed using microsatellite markers close to the TPO and c-mpl genes on chromosomes 3q26.3-q27 and 1p34, respectively. The absence of cosegregation within the affected family indicated that these genes, as well as two other candidate loci on chromosomes 11 and 21, are not responsible for this hereditary dominant form of thrombocytopenia. A genome-wide search and subsequent identification of the gene will provide new insight into the pathogenesis of this disorder.

Blood Platelets↗
PubMed2006

Whole blood aggregometry for evaluation of the antiplatelet effects of clopidogrel.

INTRODUCTION: The marked interindividual variability in platelet inhibition even after administration of high loading doses of clopidogrel raised the question whether monitoring of antiplatelet effects in patients undergoing percutaneous coronary intervention (PCI) can improve clinical outcome. Established methods for monitoring antiplatelet drug activity such as optical aggregometry and determination of surface protein expression are not suitable for routine bedside testing. MATERIAL AND METHODS: We therefore compared the applicability of whole blood impedance aggregometry (20 micromol/L ADP) and the whole blood bedside ULTEGRA assay with ADP-cartridges (20 micromol/L) with optical aggregometry in platelet-rich plasma and determination of surface protein expression (P-Selectin and activated GPIIb/IIIa) by flow cytometry. We analyzed samples obtained from 27 patients scheduled for elective PCI who received a loading dose of 600 mg of clopidogrel. Blood samples were withdrawn before clopidogrel, before PCI and 24h thereafter. RESULTS: Platelet aggregation assessed by optical aggregometry (20 micromol/L ADP) declined from 65+/-9% (baseline) to 42+/-12% (PCI) and 45+/-13% (24h; p<0.01). Expression of surface proteins displayed a similar time course. Platelet aggregation determined by impedance aggregometry decreased from 4.6+/-4.0 Omega (baseline) to 0.1+/-0.3 Omega (PCI) and 0.5+/-1.1 Omega (24h) with no detectable residual platelet aggregation during PCI in 88% of patients. The ULTEGRA assay showed only slight changes after administration of clopidogrel. Correlation analysis between the various assays revealed significant correlations only between optical aggregometry and flow cytometry. CONCLUSIONS: The results indicate that both of the whole blood assays cannot substitute for optical aggregometry or determination of surface proteins in the assessment of clopidogrel-induced platelet inhibition.

Angioplasty, Balloon, Coronary↗
PubMed2003

Inherited thrombocytopenias: a proposed diagnostic algorithm from the Italian Gruppo di Studio delle Piastrine.

BACKGROUND: Although no epidemiological study has so far been performed, inherited thrombocytopenias are considered to be very rare based on the number of case reports in the literature. However, diagnosis of these disorders is often difficult and requires competences that are limited to specialized centers. We, therefore, suspect that inherited thrombocytopenias are underreported because their diagnosis is often missed. OBJECTIVES: The aim of this study was to develop a diagnostic algorithm that utilizes the simplest possible diagnostic tests and that can also be used in centers that are not highly specialized. METHODS: The basic features of the diagnostic algorithm (definition and classification of hereditary thrombocytopenias, laboratory tests, sequence of investigations) were discussed by the members of the Italian Gruppo di Studio delle Piastrine during two meetings held in October 2000 and 2001. The sources of information were literature and personal experience. The final proposed diagnostic algorithm was produced by the authors of this paper and approved during a third meeting in May 2002. PERSPECTIVES: A definite diagnosis for patients with hereditary thrombocytopenias serves many purposes. It is essential to define the prognosis of the patients and to identify the best therapeutic approach. It also defines the risk of transmitting the disorder to progeny and, in many cases, allows prenatal diagnosis. Finally, several pieces of evidence indicate that not all the genetic thrombocytopenias have yet been identified. Exclusion of known disorders by accurate investigation is, therefore, the starting point for the discovery of these new illnesses.

Algorithms↗
PubMed2005

Effects of clopidogrel and aspirin in combination versus aspirin alone on platelet activation and major receptor expression in patients after recent ischemic stroke: for the Plavix Use for Treatment of Stroke (PLUTO-Stroke) trial.

BACKGROUND AND PURPOSE: Clopidogrel is widely used in patients after recent ischemic stroke; however, its ability to yield additional antiplatelet protection on top of aspirin has never been explored in a controlled study. To determine whether clopidogrel with aspirin (C+ASA) will produce more potent platelet inhibition than aspirin alone (ASA) in patients after ischemic stroke, we conducted the Plavix Use for Treatment of Stroke trial. METHODS: Seventy patients after ischemic stroke were randomly assigned to C+ASA or ASA groups. Platelet studies included aggregometry; cartridge-based analyzers; expression of PECAM-1, P-selectin, GP IIb/IIIa (antigen and activity), vitronectin receptor, and formation of platelet-leukocyte microparticles by flow cytometry. Platelet tests were performed at baseline and after 30 days after randomization. RESULTS: There were no deaths, hospitalizations, or serious adverse events. There were no differences in the baseline platelet characteristics between C+ASA and ASA groups, or significant changes in platelet parameters in the ASA group, except diminished collagen-induced aggregation (P=0.001). In contrast, therapy with C+ASA resulted in a significant inhibition of platelet activity assessed by ADP- (P=0.00001) and collagen-induced (P=0.02) aggregation; closure time prolongation (P=0.03), and reduction of platelet activation units with Ultegra (P=0.00001); expression of PECAM-1 (P=0.01), and GP IIb/IIIa activity with PAC-1 (P=0.02) when compared with ASA group. Therapy with C+ASA also resulted in the reduced formation of platelet-leukocyte microparticles (P=0.02). CONCLUSIONS: Treatment with C+ASA for 1 month provides significantly greater inhibition of platelet activity than ASA alone in patients after recent ischemic stroke in the frame of the small randomized trial.

Aged↗
PubMed2005

Study for determination of the optimal cessation period of therapy with anti-platelet agents prior to invasive endoscopic procedures.

BACKGROUND: Anti-platelet agents are widely used for the treatment and prevention of thrombotic diseases. On the other hand, continuation of anti-platelet agents increases the risk of hemorrhagic complications in gastrointestinal endoscopy, and cessation of anti-platelet agents exposes the patient to the risk of thromboembolism. Only a few studies have actually studied the whether a cessation period is required prior to endoscopic procedures and if so, the optional duration of the period. The present study assessed the time course of primary hemostasis after the cessation of anti-platelet agents. METHODS: Eleven healthy men (age range, 19-29 years) were assigned to each of the following regimens: aspirin (ASA; 100 mg/day), ticlopidine (TP; 300 mg/day), and a combination of ASA (100 mg/day) and TP (300 mg/day) for 7 days. There was a washout period of more than 3 weeks between each regimen. A quantitative bleeding time test (QBT test) and platelet aggregation test were performed before the beginning of administration, on the last day of administration, and at 1, 3, and 5 days after cessation, and also at 7 days after cessation for the combination regimen. RESULTS: The average bleeding time (BT) and total bleeding loss volume (Tv) of the 11 subjects after administration of the three regimens were significantly increased compared with those before administration. With the administration of ASA, increases of BT and Tv at 3 days after cessation were not significant. The Tv at 5 days after cessation of TP was not significantly increased. With the combination regimen, the BT and Tv at 7 days after cessation were not significantly increased. CONCLUSIONS: A 3-day cessation period for ASA, a 5-day cessation period for TP, and a 7-day cessation period for ASA+TP administration seem to be sufficient.

Adult↗
PubMed1998

Shear-induced platelet adhesion and aggregation on subendothelium are increased in diabetic patients.

Increased platelet aggregation has been suggested to play a role in the accelerated atherosclerosis of diabetics. However the physiological relevance of the aggregation tests has been questioned. The purpose of this study was to determine platelet activation in diabetic patients, using a novel device--the cone and plate(let) analyzer--to measure shear-induced platelet adhesion and aggregation on extracellular matrix (ECM). Whole blood platelet adhesion and aggregation in patients with noninsulin-dependent diabetes mellitus (n=82) and in nondiabetic controls (n=71) were compared. Clinical and laboratory characteristics of the diabetic patients were analyzed for possible correlation with parameters of platelet activity. Patients with diabetes had a significantly increased platelet activation compared to nondiabetic subjects, demonstrated by an increased adhesion to the ECM (surface coverage, 23% [95% confidence interval, 22-25%] vs. 19% [95% confidence interval, 18-20%], respectively) and an increased average size of the ECM-bound aggregates (54 microm2 [95% confidence interval, 51-57 microm2] vs. 47 microm2 [95% confidence interval, 43-51 microm2], respectively). Platelet adhesion in the diabetic group was found to correlate with triglyceride levels (r=0.36) and hematocrit values (r=0.31) and inversely with high-density lipoprotein cholesterol levels (r=0.30). There were no correlation, however, between parameters of platelet reactivity and duration of diabetes, vascular complications and low-density lipoprotein levels. Our data demonstrate an increased platelet adhesion and aggregation in diabetic patients and suggest a modulatory role of diabetic dyslipidemia.

Adult↗
PubMed2001

Acute hyperglycemia increases soluble P-selectin in male patients with mild diabetes mellitus.

The aim of this study was to examine if acute hyperglycemia (an oral glucose tolerance test) activates platelet function, endothelial cells or thrombin generation in diabetic patients and healthy controls. Eleven males with mild type II diabetes mellitus and 11 healthy male volunteers, matched for age and body mass index, were investigated before and after the glucose load. Soluble P-selectin, von Willebrand factor antigen and markers of thrombin generation in plasma were determined by immunoassays, and platelet P-selectin expression (unstimulated and agonist-stimulated) by flow cytometry in whole blood. Acute hyperglycemia elevated plasma soluble P-selectin from 32.5 to 50.9 ng/ml in the diabetic group (P = 0.05) but not in the controls (from 27.3 to 28.8 ng/ml; P = 0.6). Also, soluble P-selectin levels were higher in patients with diabetes than in healthy controls during hyperglycemia, but not in the fasting state. Adenosine diphosphate- and thrombin-induced platelet P-selectin expression was slightly, but significantly, decreased by the glucose load, whereas platelet P-selectin expression in unstimulated samples was not affected. Plasma levels of von Willebrand factor and thrombin generation were similar in patients and controls, and were not altered by hyperglycemia. In conclusion, we found that acute hyperglycemia elevates soluble P-selectin in plasma in males with mild type II diabetes mellitus. Our observation of unaltered plasma levels of the endothelial marker von Willebrand factor is in agreement with platelets being the main source of P-selectin released into plasma following hyperglycemia. Thus, platelets in individuals with type II diabetes may be more susceptible to hyperglycemia than platelets in non-diabetic individuals.

Adenosine Diphosphate↗
PubMed1988

[Measurement of bleeding time and study of thrombocyte aggregation. Standardization of methods, normal values and results in patients with suspected hemorrhagic diathesis].

Bleeding time measurement and investigation of platelet aggregation in platelet rich plasma (PRP) are routine procedures for the diagnosis of defects in primary hemostasis. These tests are subject to methodological difficulties and should be well standardized in each individual laboratory. - In the present study, bleeding time was measured using the Simplate II device in 40 normal subjects. Furthermore, platelet aggregation in PRP induced by ADP, collagen, arachidonate, and ristocetin was examined. 26 patients referred for investigation of a suspected mild bleeding disorder, who had a normal plasmatic coagulation profile, a normal von Willebrand factor activity, and a normal platelet count, were similarly studied. - Based on the reference values established in the 40 normal subjects, platelet aggregation was found to be pathologic in 7 patients and normal in 12. In 7 patients platelet aggregation was considered to be borderline-pathologic as defined by the range of platelet aggregability found in the 10% of our normal subjects showing the weakest aggregation responses. Bleeding time was prolonged in only 3 patients whereas it was normal in the remaining 23. There was strong evidence of a hemostatic defect as assessed by systematic patient history in 6 out of 7 patients with pathologic platelet aggregation, but in only 3 out of 19 showing normal or borderline-pathologic aggregation. - Pathologic platelet aggregation, therefore, represents not only an abnormal laboratory finding but is likely to be associated with a hemorrhagic diathesis. Platelet aggregation studies do not permit etiologic diagnosis of the thrombocytopathy except for the well-defined membrane glycoprotein deficiencies. The bleeding time appeared to be of low sensitivity for the diagnosis of mild platelet dysfunction.

Adolescent↗
PubMed1990

[Bleeding time and volume in vitro by THROMBOSTAT].

We tested an in vitro system simulating bleeding time reported by Kratzer et al. Primary hemostasis was studied perfusing an artificial vessel with citrated blood under a constant pressure of 40 mmHg, measuring the blood volume perfused (bleeding volume) and the time until blood flow stopped (bleeding time). The artificial vessel consists of a glass capillary simulating arteriole and a filter covered with collagen type I to provide a surface for the adhesion of platelets. The bleeding volume (mean +/- SD microliters) was 317.7 +/- 93.8 in controls (n = 19), 487.3 +/- 242.1 in idiopathic thrombocytopenic purpura (n = 9), 666.8 +/- 224.1 in aplastic anemia and paroxysmal nocturnal hemoglobinuria (n = 4), greater than 820 in von Willebrand's disease (n = 3), 231.0 +/- 74.5 in hemophilia A (n = 3), 499.0 +/- 269.4 in liver cirrhosis (n = 6), and 457.7 +/- 229.0 in myeloproliferative disorders (n = 11). When citrated blood was applied to this system after incubation with monoclonal antibodies (MoAb) to von Willebrand factor or platelet membrane glycoprotein Ib (GPIb), bleeding volume was significantly increased while no effects were observed after incubation with MoAb to GPIIb/IIIa, factor VIII: CAg and factor XIIIa. These data suggest that in vitro model of primary hemostasis could be used for not only diagnosing bleeding disorders although 'time' is not reliable, but also investigating the mechanisms of hemostasis.

Antibodies, Monoclonal↗
PubMed1984

Clinical evaluation of a new test of hemostasis: the Filter Bleeding Time.

The clinical value of a new in vitro test of hemostasis, which we have called Filter Bleeding Time (FBT), was determined in 59 patients referred because of a suspected bleeding disorder. FBT is based on the progressive slowing of the drop rate of citrated blood through a filter of woven Dacron under constant pressure as platelet aggregates occlude the filter. The value for FBT is defined as the time when the blood drop interval has reached 1 minute. The Mayo modification of the Ivy bleeding time (IBT) was performed in all patients; platelet response to ADP, collagen, epinephrine and arachidonate was performed in 24 patients. In 30 normal volunteers FBT measured 1-3 hr after venipuncture was 2.8 +/- 1.5 (means +/- 1SD) min. The FBT was prolonged in 3 of 3 patients with Glanzmann's thrombasthenia, 2 with disseminated intravascular coagulation, 1 with chronic lymphocytic leukemia, 1 with myelofibrosis, and 1 who had taken aspirin. In 6 patients FBT was prolonged while IBT was normal: 4 after taking aspirin, 2 with polycythemia vera. All 6 had reduced platelet aggregation (PA) to ADP (5 microM), collagen (2 mg/ml), epinephrine (5 microM) and/or arachidonate (1.7 mM). In 3 patients FBT was normal while IBT was abnormal: 1 with disseminated intravascular coagulation, 2 undiagnosed; 1 of these 3 had abnormal PA. Of 6 patients with von Willebrand's disease, FBT was prolonged in 5 and borderline in 1; IBT was prolonged in 3, normal in 1, and not done in 2 infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic Acids↗
PubMed1992

[Evaluation of platelet aggregation test by grading curve].

In order to standardize the platelet aggregation test, we used the grading curve (GC) produced by plotting four concentrations (0.5, 1.0, 2.0 and 4.0 microM) of ADP and four concentrations (0.25, 0.5, 1.0 and 2.0 micrograms/ml) of collagen, which are aggregation inducers, along the horizontal axis and plotting their individual rates (%) of aggregation 5 minutes after administration, along the longitudinal axis. The degree of platelet aggregation was classified in 6 stages (Types III, II, I, 0, -I and -II), ranging from marked increase to marked decrease, according to the GC of ADP aggregation in healthy subjects. Type I or 0 ADP aggregation was observed in 78% of the subjects, and Type I collagen aggregation was observed in about 50% of the subjects, whereas patients with cerebral infarction showed distinct increases in Type III and II aggregations of both ADP and collagen. In most patients who were treated with antiplatelet drugs, the aggregation were Type 0, -I or -II. The concentration of inducer, which corresponded to the maximum 50% value of the GC (Max 50) was significantly correlated with the minimum concentration (threshold concentration) in ADP aggregation, at which secondary aggregation was induced even if it was reversible, and with the minimum concentration (threshold concentration) in collagen aggregation, at which the aggregation rate 5 minutes after administration increased to 50% or higher. The GC of platelet aggregation seemed to enable easy determination of the degree of aggregation, and was also considered to be useful for monitoring platelet aggregation during the administration of antiplatelet drugs.

Adult↗
PubMed2006

Aspirin resistance detected with aggregometry cannot be explained by cyclooxygenase activity: involvement of other signaling pathway(s) in cardiovascular events of aspirin-treated patients.

OBJECTIVES: Although the concept of aspirin resistance is extensively reported in medical literature, its precise mechanisms and clinical outcomes are largely unknown. In this study, we examined individual thromboxane biosynthesis and platelet aggregation in aspirin-treated patients, and whether the results of a platelet aggregation test influenced clinical outcomes. RESULTS: Subjects taking 81 mg of aspirin (n = 50) and controls (n = 38) were evaluated for platelet aggregation and platelet cyclooxygenase-1 (COX-1) activity by measuring collagen-induced thromboxane B2 production. For aggregometry, both light transmission (LT) and laser-light scattering methods were employed to quantitatively evaluate aggregate sizes and numbers. Aspirin treatment resulted in the inhibition of collagen-induced platelet aggregation, particularly the transition from small to large platelet aggregates. Although platelet COX-1 activity seemed to be uniformly inhibited in all patients, platelet aggregation studies showed great inter-individual differences; variation in platelet COX-1 activity only accounted for 6-20% of the individual aggregations. Factor analysis revealed the existence of a common factor (other than platelet COX-1) that explained 48.4% of the variations in platelet aggregation induced by collagen, adenosine diphosphate (ADP), and collagen-related peptide. We then prospectively enrolled 136 aspirin-treated patients in our study, and we found that being in the upper quartile level of LT, or with large aggregate formation induced by collagen, was an independent risk factor for developing cardiovascular events within 12 months [hazard ratio (HR) = 7.98, P = 0.008 for LT; HR = 7.76, P = 0.007 for large aggregates]. On the other hand, the existence of diabetes mellitus was an independent risk factor for overall outcomes (HR 1.30-11.9, P = 0.015-0.033). CONCLUSIONS: Aspirin resistance expressed as unsuppressed platelet COX-1 activity is a rare condition in an out-patient population. Other factor(s) affecting collagen-induced platelet aggregation may influence early outcomes in aspirin-treated patients.

Aged↗
PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗
PubMed2001

Acetylsalicylic acid and microembolic events detected by transcranial Doppler in symptomatic arterial stenoses.

BACKGROUND: In patients with symptomatic carotid artery stenosis, high-intensity transient signals detected by transcranial Doppler (TCD) have been related to particulate microemboli originating at the stenotic lesion. The occurrence of these microembolic events within the Doppler spectrum should be influenced by antithrombotic agents of proven efficacy in these patients mainly by reducing cerebral embolism. METHODS: Seventy-four of 192 consecutive patients with symptomatic arterial stenosis in the anterior circulation and clinical symptoms within the last 30 days underwent 1-hour bilateral TCD monitoring. Patients were selected, if they presented temporal bone windows enabling transcranial insonation, revealed normal Doppler CO2 test excluding hemodynamic impairment, had not received antithrombotic therapy other than acetylsalicylic acid (ASA) before sonographic examination, and gave informed consent to 1-hour monitoring which could be performed immediately on admission/presentation of the patient at the Department of Neurology. RESULTS: Microembolic events were detected in 38 patients (51%). The proportion of patients with events among 26 patients without antithrombotic medication was 73% as compared with 40% in 48 patients receiving ASA at the time of TCD monitoring (p = 0.023). Multivariate analysis including time from ischemia to TCD, presence and start of ASA prevention, degree and localization of stenosis, and presence of a single or recurrent ischemia revealed that absence of an ASA prevention (odds ratio OR 7.1, 95% confidence interval CI 1.6-31.4, p = 0.010), recurrent ischemic events (OR 7.1, 95% CI 1.6-32.7, p = 0.011), and extracranial localization of the stenosis (OR 3.8, 95% CI 1.1-13.2, p = 0.038) were independent predictors for microembolic events. CONCLUSION: In patients with symptomatic arterial stenosis, the absence of an ASA medication is associated with the occurrence of TCD-detected microembolic events, suggesting a relation between these events and ASA-sensitive microemboli from the stenotic lesion.

Aged↗
PubMed2006

Monitoring platelet inhibition after clopidogrel with the VerifyNow-P2Y12(R) rapid analyzer: the VERIfy Thrombosis risk ASsessment (VERITAS) study.

INTRODUCTION: Clopidogrel inhibits platelet P2Y12 ADP receptors, while ADP, as an inductor of aggregation, stimulates both P2Y12 and P2Y1 platelet receptors. Despite a clinical loading dose routine with clopidogrel, some patients still experience coronary stent thrombosis suggesting persistent platelet activation. The VerifyNow-P2Y12 is a rapid assay that test platelet activity over 3 min and uses of the combination of ADP and prostaglandin E1 (PGE1) to directly measure the effects of clopidogrel on the P2Y12 receptor. ADP is used to maximally activate the platelets by binding to the P2Y1 and P2Y12 platelet receptors, while PGE1 is used to suppress the ADP-induced P2Y1-mediated increase in intracellular calcium levels. OBJECTIVE: The VERIfy Thrombosis risk ASsessment (VERITAS) was a prospective study designed to measure platelet response to clopidogrel therapy in subjects with multiple risk factors or history of vascular disease using this novel point-of-care assay. METHODS: 166 participants were enrolled in 4 participating sites. Data from 147 participants were analyzed after exclusion of 19 patients due to protocol violations. Platelets were assessed twice at baseline (before clopidogrel) and at 24 h post-loading 450 mg (110 participants) or 7 days after chronic clopidogrel treatment (75 mg/day) (37 patients). All participants received aspirin 81-325 mg for at least 2 days before the study enrollment. Results from the VerifyNow-P2Y12 assay are reported in P2Y12 reaction units (PRU). RESULTS: Clopidogrel therapy resulted in a mean 64.0+/-25.3% PRU reduction. No participant reached PRU inhibition below 10% of baseline. Distribution of PRU values for the VerifyNow-P2Y12 assay shows a separation from baseline to post-clopidogrel assay values with some overlap due to high inter-individual variations in response. CONCLUSIONS: VerifyNow-P2Y12 is a reliable, fast and sensitive device suitable for monitoring of platelet inhibition during clopidogrel therapy.

Adenosine Diphosphate↗
PubMed1990

Non-occlusive bleeding times may improve the value of Ivy bleeding times.

The present studies measured bleeding times, without venous occlusion, in a series of patients, whose bleeding times (+ venostasis) consistently exceeded 20 min. During these tests, the amount of blood loss (expressed as mg/min) was also quantitated. To allow comparison, normal controls were studied before and following aspirin ingestion. In normal controls, the mean standard Ivy bleeding time was 5.0 with a range of 2.5 to 7.5 min. Two hours after aspirin (650 mg), this increased to 7.3 min (range 4.0-12.0). For comparison, the non-occlusive bleeding time averaged 3.8 min (1.0-6.5) and after aspirin 5.3 min (2.5-11.5). The measured amount of blood loss was 5.0 mg/min (0-10.5 mg/min) under all of the above conditions. At the other extreme, patients with severe bone marrow failure had occluded and non-occluded bleeding times in excess of 20 min. Moreover, these were often associated with excess blood loss. By contrast, patients with "Ivy" values greater than 20 min in association with platelet counts greater than 10,000/microliters had unpredictable bleeding parameters. In the latter group, the non-occluded values ranged from 1 to greater than 20 min. Of particular note, the non-occlusive times appeared to correlate with spontaneous bleeding manifestations. Only a rare patient (1/37), whose non-occluded value was less than 20 min, had worrisome bleeding. By contrast, serious bleeding manifestations were observed in 39% whose non-occluded value exceeded 20 min. This was even higher (64%) in those with a non-occluded value greater than 20 min and excess blood loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Arm↗
PubMed1994

Heparin-associated thrombocytopenia: isolation of the antibody and characterization of a multimolecular PF4-heparin complex as the major antigen.

Sera of 34 patients with heparin-associated thrombocytopenia (HAT), giving a positive result in the serotonin release assay (SRA), were assessed in a platelet factor 4 (PF4)/heparin ELISA. Three sera revealing indeterminate results in the SRA and 10 control sera were also investigated. Both tests correlated closely (Kappa 0.742; p = 2.67 x 10(-7)), but one positive serum in the SRA was negative in the pF4/heparin ELISA. We have isolated the HAT antibodies by absorbtion and elution of HAT sera using endothelial cells (HUVEC). Eluates gave similar results as the sera in the PF4/heparin ELISA (Kappa 0.837, p = 9.26 x 10(-9)), and they also correlated very closely with the SRA (Kappa 0.888; p = 8.89 x 10(-10)). This demonstrates that HAT antibodies bind to the same epitope on platelets and on endothelial cells. High heparin concentrations released PF4 in a dose dependent manner from microtiter plates if PF4/heparin, but not if PF4 alone, was covalently linked. Concomitant to the release of PF4, binding of HAT antibodies to PF4/heparin decreased, as indicated by the median optical density (OD) values of OD 0.88 in the presence of buffer compared to OD 0.181 in the presence of 100 IU/ml heparin. The latter values were similar to those obtained when plates were coated with PF4 alone (median OD 0.203). Binding of three eluates was not inhibited by high heparin concentrations and they reacted also with PF4 alone. We conclude that multimolecular PF4/heparin complexes represent the major antigen in HAT. These multimolecular complexes might present several epitopes and form immune complexes after HAT antibody binding which activate platelets via the FcRII. In a few cases, PF4 alone can be recognized by the antibody. However, there is also evidence that other molecules might be involved in some patients.

Antibodies↗