Greater Platelet Activation Research Articles

Impact of chronic psychological stress on platelet membrane fatty acid composition in a rat model of type 1 diabetes Mellitus

BackgroundChronic stress and diabetes mellitus are highly associated with oxidative stress and inflammation, resulting in cell membrane disruption and platelet activity. This study aims to evaluate the impact of chronic psychological stress on the composition of the platelet phospholipid membrane and platelet activation in type 1 diabetes mellitus (T1DM).MethodsWe enrolled 35 mature healthy female Wistar rats and randomly divided them into 4 groups, namely the control group (n = 9), stress group (n = 10), T1DM group (n = 8), and T1DM + Stress group (n = 8). The Wistar rats were treated in different experimental conditions for 28 days while being provided free access to feed and water. The concentration of corticosterone in blood serum and hair samples was measured using a competitive enzyme-linked immunosorbent assay. Gas chromatography-mass spectrometry was conducted to identify the methyl esters of fatty acids (FAs) in the platelet phospholipid membrane. A quantitative determination of 11-dehydro-thromboxane B2 in the blood serum was also performed using a competitive enzyme-linked immunosorbent assay.ResultsAfter 28 days, the concentration of corticosterone in blood serum (ng/mL) was observed to be higher in the stress group as compared to the T1DM and T1DM + Stress groups (P = 0.031 and P = 0.008, respectively). The percentage of C 16:0 FA in the platelet membrane was greater in the T1DM + Stress group, but its levels of C 20:1 omega (ω) 9 FA, including C 18:3ω3 FA, C 20:5ω3 FA, and the total sum of ω3 FAs, were lower as compared to the control group (P = 0.016; P = 0.016; P = 0.031; P = 0.016, P = 0.031). The concentration of 11-dehydro-thromboxane B2 in blood serum (pg/mL) was observed to be higher in the stress group than in rats with T1DM (P = 0.063).ConclusionChronic psychological stress is related to higher levels of corticosterone, saturated FAs acids in the platelet membrane, and greater platelet activation. This study proves how a low percentage of unsaturated fatty acids in the DM and stress groups indicates the disturbing impact of the oxidative/inflammatory environment to lipid metabolism and neuroendocrine response.

Abstract TP125: Relationships Of Female Sex With Viscoelastic Hemostatic Assay Coagulation Characteristics After Intracerebral Hemorrhage

Introduction: There are described differences in coagulation between females and males. Specifically, female sex is associated with greater platelet activation and stronger clotting characteristics. It is unclear whether there are relevant coagulation differences identifiable between female and male patients suffering from intracerebral hemorrhage (ICH). Hypothesis: Female sex will be associated with stronger clotting characteristics on whole blood viscoelastic hemostatic assay testing. Methods: Spontaneous ICH patients admitted and enrolled into a prospective observational ICH cohort study between 2009-2020 and who received baseline viscoelastic hemostatic assay testing (Rotational Thromboelastometry: ROTEM) were assessed. Patients with prior anticoagulant use, patients receiving hemorrhage control therapies prior to ROTEM, and secondary etiologies of ICH were excluded from the analysis. Female sex was assessed as the primary exposure variable. The following ROTEM clotting parameters were assessed as the outcome: Coagulation Time (CT) and Maximum Clot Firmness (MCF). We assessed relationships of female sex with these separate ROTEM parameters using multivariable linear regression analyses after adjusting for relevant covariates. Results: Of 57 ICH patients included for analyses, mean age was 65 (SD 14.1), 47% were female, and the median ICH volume was 20.6 mL (IQR 10.1-43.3). There were no baseline intergroup sex differences in demographics, age, or ICH characteristics. Female sex was associated with increased EXTEM MCF (ß 0.323, p<0.05), signifying greater clotting strength, after adjusting for age, race, baseline hematoma volume, and ICH location. Female sex was not associated with other ROTEM parameters. Conclusions: We identified that female sex was associated with stronger clotting characteristics on ROTEM viscoelastic testing. Further work is required to clarify the clinical significance of these findings and their potential specific impacts on radiographic, complication, and clinical outcomes after ICH.

Activated platelets in central venous catheters: a flow cytometry and numerical simulation approach

The central venous catheter that is inserted in patients undergoing hemodialysis can cause hemodynamic instability and trigger complications such as thrombus formation. The objective of this study was to investigate hemostatic and numerical influences on thrombus formation in patients undergoing hemodialysis with a central venous catheter. Participants were assigned to three groups: I: clinical and laboratorial healthy individuals matched by sex and age (controls); II: participants after one month of insertion of the catheter and III: participants after 4 months of insertion of the catheter. Platelet activation was investigated by GPIIb/IIIa and p-selectin expressions using flow cytometry. A three-dimensional model of the catheter was constructed in the numerical simulation for the calculation of partial differential equation of a platelet activation model. A significant difference was detected by the expression of p-selectin comparing the group I (33.42 ± 4.74), group II (40.79 ± 5.54) and group III(51.00 ± 7.21) (p < 0.0001). The median values for GPIIb/IIIa were 10426 (10029-10721), 13921 (13412-15652) and 19946 (18714-21815) after catheter insertion (p < 0.0001), for groups I, II and III, respectively. Excluding the first arterial orifice, venous orifices tend to have greater platelet activation when compared to the other arterial orifices. The results of this study showed the influence of arterial and venous lateral orifices in stimulating the development of thrombi associated with the activation of platelet markers the longer the catheter was used

Is “one size fits all” anti-aggregation really effective? Variability in the response to P2Y12 receptor inhibitors in obese patients

Abstract Background Different “ex vivo” studies have shown both a greater platelet activation and higher rates of resistance to clopidogrel in obese patients. Although there is less evidence, less prasugrel activity has also been observed in these patients. Our aim was to study the variability of the response to clopidogrel, ticagrelor and prasugrel in obese patients, defined as a body mass index ≥30. Methods Prospective, multicenter, observational, pharmacodynamic study, conducted in a Spanish population of patients with an acute coronary syndrome (ACS) treated with percutaneous coronary intervention (PCI) and double anti-aggregation with acetylsalicylic acid and a P2Y12 receptor inhibitor. Platelet function tests were performed the morning after the ICP and 30 days after it, including: 1) VerifyNow P2Y12 assay; 2) multiple electrode aggreometry (Multiplate); and 3) VASP analysis. Results Of the total patients included (988), 300 were obese (30.3%). The obese group was younger (62.8±12 years vs 64.9±12), had a higher incidence of arterial hypertension (76.3% vs. 56.7%), diabetes mellitus (35% vs. 27.5%); and lower incidence of chronic kidney disease (7.7% vs. 17%). There were no differences in the acute phase (day 1 after PCI) in the pharmacodynamic response to any of the P2Y12 inhibitors used. After 30 days, greater platelet aggregation (decreased response) was documented in obese patients treated with prasugrel according to VASP tests (PRI in non-obese 23.9±13% vs. 30.4±14.7% in obese, p 0.035) and MEA (area under the aggregation units curve in non-obese 251.7±104.1 vs 320±166.7 in obese, p 0.007) and a numerical trend with VerifyNow. A trend in the same direction was also observed in patients treated with clopidogrel that did not reach statistical significance with all the platelet function tests used. No differences were observed in the ticagrelor group. Conclusion Obese patients with an ACS treated with PCI have a worse response to thienopyridines than non-obese patients in the maintenance phase of antiaggregant treatment, while the response to ticagrelor is not affected by obesity. Completing the clinical follow-up proposed by the registry is necessary to know if these differences have an implication in cardiovascular events. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Fondo de Investigaciones Sanitarias (FIS)

INTERRELATIONS BETWEEN GROWTH DIFFERENTIATION FACTOR 15, P-SELECTIN AND GALECTIN-3 AND CLINICAL COURSE IN PATIENTS WITH ARTERIAL HYPERTENSION AND TYPE 2 DIABETES MELLITUS

The aim of our study was to determine the base levels of Growth Differentiation Factor 15, P-selectin and Galectin-3 in blood plasma in patients with AH and T2DM and to assess their association with the diseases clinical course. Materials and methods. A total of 121 patients were included in our study (60 female and 61 male, mean age 64.7±10.6 years, with AH and/or T2DM). Patients were divided into three groups: 1st group with AH only (51 patient), 2nd group with AH and T2DM (57 patients) and 3rd group with T2DM only (13 patients, control group). GDF-15, Galectin-3 and P-selectin tests were performed using standard enzyme-linked immunosorbent assay kits (ELISA). Results. Compared with AH without T2DM and T2DM only groups, AH with T2DM group had a statistically significant higher level of GDF-15. Grade 3 hypertension group had a significantly lower level of GDF-15 compared with Grade 1&2 hypertension groups. P-selectin mean level was significantly higher in Grade 3 hypertension group GDF-15 compared with Grade 1&2 hypertension groups. We observed weak correlation between Galectin-3 and GDF-15 in blood plasma, which was confirmed by linear regression analysis. Conclusions. A combination of hypertension and type 2 diabetes mellitus revealed a significant increase of GDF-15 levels in compare with patients with only hypertension or type 2 diabetes mellitus, which may be due to a greater response to oxidative stress and low-intensity systemic inflammation. P-selectin mean level was higher in patients with grade 3 hypertension, which reflects a greater platelet activation as a part of the systemic inflammatory response. Galectin-3 mean level was higher in patients with stage 3 hypertension compared with patients with stages 1 and 2 due to possibly more pronounced fibrosis progression.

Shear Stress-Induced Total Blood Trauma in Multiple Species.

The common complications in heart failure patients with implanted ventricular assist devices (VADs) include hemolysis, thrombosis, and bleeding. These are linked to shear stress-induced trauma to erythrocytes, platelets, and von Willebrand factor (vWF). Novel device designs are being developed to reduce the blood trauma, which will need to undergo in vitro and in vivo preclinical testing in large animal models such as cattle, sheep, and pig. To fully understand the impact of device design and enable translation of preclinical results, it is important to identify any potential species-specific differences in the VAD-associated common complications. Therefore, the purpose of this study was to evaluate the effects of shear stress on cells and proteins in bovine, ovine, and porcine blood compared to human. Blood from different species was subjected to various shear rates (0-8000/s) using a rheometer. It was then analyzed for complete blood counts, hemolysis by the Harboe assay, platelet activation by flow cytometry, vWF structure by immunoblotting, and function by collagen binding activity ELISA (vWF:CBA). Overall, increasing shear rate caused increased total blood trauma in all tested species. This analysis revealed species-specific differences in shear-induced hemolysis, platelet activation, and vWF structure and function. Compared to human blood, porcine blood was the most resilient and showed less hemolysis, similar blood counts, but less platelet activation and less vWF damage in response to shear. Compared to human blood, sheared bovine blood showed less hemolysis, similar blood cell counts, greater platelet activation, and similar degradation of vWF structure, but less impact on its activity in response to shear. The shear-induced effect on ovine blood depended on whether the blood was collected via gravity at the abattoir or by venepuncture from live sheep. Overall, ovine abattoir blood was the least resilient in response to shear and bovine blood was the most similar to human blood. These results lay the foundations for developing blood trauma evaluation standards to enable the extrapolation of in vitro and in vivo animal data to predict safety and biocompatibility of blood-handling medical devices in humans. We advise using ovine venepuncture blood instead of ovine abattoir blood due to the greater overall damage in the latter. We propose using bovine blood for total blood damage in vitro device evaluation but multiple species could be used to create a full understanding of the complication risk profile of new devices. Further, this study highlights that choice of antibody clone for evaluating platelet activation in bovine blood can influence the interpretation of results from different studies.

Abstract 12495: Enhanced Thrombin Activity in Biglycan-deficient Mice Promotes Vascular Inflammation in Murine Atherosclerosis

Introduction: Thrombin signalling initiates inflammatory events directly and through activation of platelets. Endogenous and pharmacologic inhibitors of thrombin are therefore of relevance during atheroprogression and for therapeutic intervention. The small leucine-rich proteoglycan biglycan (BGN) is thought to inhibit thrombin activity by activation of heparin cofactor II. Hypothesis: Genetic deletion of BGN affects thrombin activity, inflammation and atherosclerosis. Methods:Male mice deficient in apolipoprotein E and BGN (ApoE-/-/Bgn-/0) were compared with their ApoE-/- littermates. Results: In ApoE-/- mice BGN was detected in the plasma and subendothelial matrix of capillaries, arterioles and in atherosclerotic plaques. In line with a role of BGN in balancing thrombin activity, ApoE-/-/Bgn-/0 mice exhibited higher activity of circulating thrombin and greater platelet activation than did ApoE-/- mice. Furthermore, higher concentrations of circulating cytokines in ApoE-/-/Bgn-/0 mice suggested a proinflammatory phenotype. Accordingly, isolated peritoneal macrophages released elevated concentrations of proinflammatory cytokines in response to Toll-like receptor stimulation. Immunohistochemistry and FACS analysis of the aorta demonstrated increased macrophage content in atherosclerotic lesions. Furthermore, ApoE-/-/Bgn-/0 mice exhibited higher aortic plaque burden and larger atherosclerotic lesions at the aortic root. Treatment with the thrombin inhibitor argatroban reversed platelet activation and aortic macrophage accumulation in ApoE-/-/Bgn-/0 mice. Finally, ApoE-/-/Bgn-/0 mice exhibited progressive dilation of the aortic arch, a pathological finding corroborated by markedly reduced collagen fibril density. Conclusions: The present results indicate that BGN plays a previously unappreciated protective role during progression of atherosclerosis by inhibiting thrombin activity and platelet activation, and ultimately macrophage-mediated plaque inflammation.

A systems approach to hemostasis: 1. The interdependence of thrombus architecture and agonist movements in the gaps between platelets

AbstractHemostatic thrombi develop a characteristic architecture in which a core of highly activated platelets is covered by a shell of less-activated platelets. Here we have used a systems biology approach to examine the interrelationship of this architecture with transport rates and agonist distribution in the gaps between platelets. Studies were performed in mice using probes for platelet accumulation, packing density, and activation plus recently developed transport and thrombin activity probes. The results show that intrathrombus transport within the core is much slower than within the shell. The region of slowest transport coincides with the region of greatest packing density and thrombin activity, and appears prior to full platelet activation. Deleting the contact-dependent signaling molecule, Sema4D, delays platelet activation, but not the emergence of the low transport region. Collectively, these results suggest a timeline in which initial platelet accumulation and the narrowing gaps between platelets create a region of reduced transport that facilitates local thrombin accumulation and greater platelet activation, whereas faster transport rates within the shell help to limit thrombin accumulation and growth of the core. Thus, from a systems perspective, platelet accumulation produces an altered microenvironment that shapes thrombus architecture, which in turn affects agonist distribution and subsequent thrombus growth.

Quality assessment of buffy‐coat‐derived leucodepleted platelet concentrates in PAS‐plasma, prepared by the OrbiSac or TACSI automated system

Buffy-coat (BC)-derived platelet concentrates (PCs) are the predominant product for platelet transfusion in many countries. Two automated systems, OrbiSac and TACSI, have been introduced in blood centres to prepare these PCs, as an alternative to the manual method. We compared the in vitro quality of PCs prepared by both methods during standard storage. Twenty primary BC pools were split into two parts, which were processed with OrbiSac and TACSI system to obtain OrbiSac PCs (O-PCs) and TACSI PCs (T-PCs), respectively. On days 1, 5 and 7 of standard storage, samples were taken and the following analysed: cell count, metabolic variables, platelet function and content of activation and proinflammatory substances. Both the OrbiSac and TACSI systems produced PCs that meet the standards for platelet products in terms of platelet and leucocyte content. In vitro evaluation pointed to the similar preservation of platelet metabolism (pH, glucose, bicarbonate and lactate) in O-PCs and T-PCs. Moreover, there were no significant differences between O-PCs and T-PCs as regards the hypotonic shock response or in the platelet aggregation profile. The OrbiSac system caused greater platelet activation, which resulted in higher concentrations of sCD62P, RANTES and sCD40L on the day the PCs were prepared. The systems OrbiSac and TACSI can be used to produce buffy-coat-derived PCs whose cell content, platelet function and metabolism are similar during standard storage. However, the preparation with the OrbiSac system induces a transient increase in platelet activation and release of proinflammatory substances.

Expression of P-selectin (CD62P) on platelets after thrombin and ADP in hypotrophic and healthy, full-term newborns

Background: Hypotrophic newborns in comparison with eutrophic newborns demonstrate a reduced blood platelet count and therefore may have haemostasis disorders. Expression of P-selectin (CD62P) on the surface of platelets is a marker of stimulated, activated blood platelets. The ability of platelets to react can be determined after the addition of the following activators: strong (thrombin) and weak (ADP).Materials and methods: We studied 48 hypotrophic newborns, 25 females and 23 males, weighing less than the 10th centile and 55 healthy, full-term newborns, 25 females and 30 males. Expression of CD62P on the surface of platelets was examined in the native state, after the addition of thrombin or ADP.Results: Hypotrophic newborns exhibited almost double the percentage of platelets expressing CD62P compared with the control group, 4.21% versus 2.88%. After the addition of thrombin, the percentage was 31.5% versus 12.5%, p < 0.001, whereas after the addition of ADP, the percentage was 9.54% versus 4.5%, p = 0.002.Conclusions: Hypotrophic newborns are capable of greater platelet activation in comparison with healthy term newborns. However, gender does not affect the expression of P-selectin.

Thromboembolism and Antithrombotic Therapy in Patients With Heart Failure in Sinus Rhythm

Heart failure (HF) represents a major and growing public health problem because of its prevalence, incidence, morbidity, mortality, and economic costs. The prevalence of HF is 2% to 3% of the general population.1 Five million Americans are affected, with >550 000 cases diagnosed each year.2 The mortality rate from severe HF remains >60% within 5 years of diagnosis, and 50% of hospitalized patients with HF require readmission within 6 months of discharge. In the US estimated costs amount to > $35 billion per year.3 Although several therapies (eg, β-blockers, angiotensin-converting enzyme [ACE] inhibitors, and cardiac resynchronization therapy) have been proven effective in improving HF outcomes, many unanswered questions about optimal treatment remain. One area of ongoing uncertainty is the appropriate role for antithrombotic therapy in patients with HF. Observational data suggest that patients with HF have an increased venous thromboembolism (VTE) risk (deep venous thromboembolism [DVT], pulmonary embolism [PE], peripheral arterial thromboembolism, and stroke).4 These epidemiological findings are supported by multiple mechanisms that can contribute to a hypercoagulable state in patients with HF. Despite this increased risk of VTE, the role of antithrombotic therapy remains unclear. In this article, we provide an overview of epidemiology, pathophysiology, clinical trial data, and therapeutic recommendations for prevention of thromboembolism in HF. We searched PubMed for articles published between 1958 and 2010 using the following search terms: epidemiology of heart failure , thromboembolism and heart failure , thrombogenesis and heart failure , anticoagulation in heart failure , antiplatelet agent and heart failure , aspirin and heart failure , bleeding risk and anticoagulation , and aspirin and angiotensin-converting enzyme inhibitors . We also studied abstracts from national and international cardiovascular meetings to identify unpublished studies using the key words anticoagulation and dilated cardiomyopathy . Data from published observational studies and secondary …

Association between depression and development of coronary artery disease: pathophysiologic and diagnostic implications

Depression and coronary artery disease (CAD) are both extremely prevalent diseases. In addition, compromised quality of life and life expectancy are characteristics of both situations. There are several conditions that aggravate depression and facilitate the development of CAD, as well as provoke a worse prognosis in patients with already established CAD: inferior adherence to medical orientations (medications and life style modifications), greater platelet activation and aggregation, endothelial dysfunction, and impaired autonomic dysfunction (lowered heart rate variability). Recent literature has shown that depression alone is becoming an independent risk factor for cardiac events both in primary and secondary prevention. As the diagnosis of depression in patients with heart disease is difficult, due to similarities of symptoms, the health professional should perform a careful evaluation to differentiate the clinical signs of depression from those related with general heart diseases. After a myocardial infarction, depression is an independent risk factor for mortality. Successful therapy of depression has been shown to improve patients’ quality of life and cardiovascular outcome. However, multicentric clinical trials are needed to support this inference. A practical liaison between qualified professionals is necessary for the better management of depressed patients with excess risk in developing CAD. Accordingly, pathophysiological and clinical implications between depression and CAD are discussed in this article.

Clopidogrel Pretreatment for Percutaneous Coronary Intervention

In trying to explain how balloon angioplasty relieved coronary narrowing, Andreas Gruentzig often displayed a photograph of footprints in fresh snow. He proposed that balloon expansion resulted in gentle, uniform plaque compression. Subsequent histological examination in the porcine coronary model and of postmortem and ultrasound findings in humans indicated more traumatic effects of angioplasty, including deep medial fissuring and adventitial stretching. Such injury causes the release of potent substances from the arterial wall that have profound vasoactive and thrombotic effects. One early response is platelet activation and deposition over the injured arterial surface, creating the substrate for thrombosis. Stent implantation appears to be associated with even greater platelet activation than balloon angioplasty alone. Importantly, the magnitude of platelet activation is associated with an increased risk for adverse clinical events after coronary intervention.1 See p 2099 Aspirin, administered as an agent to inhibit platelet activity, has been a standard component of the angioplasty protocol since the inception of the procedure. More recently, substantial evidence indicates that supplementing aspirin and unfractionated heparin with agents that antagonize the platelet glycoprotein (GP) IIb/IIIa receptor further reduces the incidence of abrupt coronary closure and the magnitude of periprocedural cardiac enzyme elevations and, in certain patient subsets, may enhance survival.2–6 To decrease the risk of stent thrombosis, practice guidelines call for augmented antiplatelet therapy (aspirin and a thienopyridine) for weeks to months after hospital discharge. In this issue of Circulation , Patti et al7 extend our knowledge about antiplatelet therapy and percutaneous coronary intervention (PCI), particularly with regard to the impact of pretreatment clopidogrel dosage and the magnitude of treatment effect that can be achieved. These investigators administered either 300 or 600 mg of clopidogrel 4 to 8 hours before cardiac catheterization to 329 patients who were potential candidates for coronary revascularization. Excluded …

Coronary artery surgery with bypass causes greater platelet activation and thrombin generation than surgery without bypass

Coronary artery surgery with bypass causes greater platelet activation and thrombin generation than surgery without bypass

Elevated platelet factor 4 and β-thromboglobulin plasma levels in depressed patients with ischemic heart disease

Clinical depression has recently been recognized as an independent risk factor for cardiac mortality in patients after myocardial infarction. The underlying mechanisms of this increased mortality remain unclear. This study investigated the hypothesis that patients suffering from ischemic heart disease (IHD) and depression concurrently may have abnormal platelet activation resulting in an increased risk of thrombosis. Platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG) were measured in young healthy control subjects, in nondepressed patients with IHD, and in depressed patients with IHD. Mean PF4 and beta-TG plasma levels in the IHD group with depression were found to be significantly higher than those of the control and IHD groups. This increase was not related to age, gender, racial difference, aspirin use, or severity of cardiac disease. This finding suggests that in depressed patients with IHD there is greater platelet activation, and may indicate an increased risk of thrombotic complications.

Time course of platelet activation following acute ischemic stroke

To assess the time course of platelet activation after acute ischemic stroke we measured the platelet protein ß-thromboglobulin (BTG) in 66 patients. Serial samples were obtained over a 3-month period. Mean values of BTG in patients with lacunar infarction were not significantly elevated at any time. In nonlacunar strokes, the mean BTG level during the first week after stroke was not significantly elevated. The mean BTG level rose in the second week and became statistically different from control (mean ± SEM; 33.1 ± 3.6 vs. 21.3 ± 2.0 IU/ml, p = 0.01). Mean values then declined to normal. Significant differences were noted among stroke subtypes. During the first week, mean values of BTG were higher in cardioembolic stroke (36.9 ± 6.2 IU/ml, p = 0.007 vs. controls) than in atherothrombotic stroke (22.1 ± 2.8 IU/ml, p = 0.82). By the second week, mean BTG values were significantly elevated for both cardioembolic (44.4 ± 8.3 IU/ml, p < 0.001) and atherothrombotic (33.8 ± 5.0 IU/ml, p = 0.01) strokes. The rise of this marker following stroke suggests that at least some of the platelet activation associated with stroke is a secondary phenomenon. Cardioembolic stroke is associated with as much platelet activation as atherothrombotic stroke and may have greater platelet activation during the first week after stroke.

The platelet release reaction in cardiovascular disease: evaluation of plasma betathromboglobulin as a marker of a prothrombotic state.

Plasma betathromboglobulin as a marker of in vivo platelet release was found to be significantly higher in 131 patients with prosthetic cardiac valves and 104 patients with coronary artery disease, compared with 133 normal individuals. Patients with double mechanical valves had a higher mean betathromboglobulin than those with single mechanical valves, who in turn had higher values than those with single heterograft valves. Thirteen patients adequately anticoagulated at the time of a thromboembolic event had significantly higher betathromboglobulin levels than 5 with thromboemboli when not anticoagulated, suggesting platelets were responsible for the emboli in the former group. The presence of coronary risk factors in normal individuals did not affect betathromboglobulin; however, when two or more risk factors were present in patients with ischaemic heart disease, mean betathromboglobulin was higher than when only one or no risk factors were present. This suggests greater platelet activation in the presence of more widespread atherosclerotic disease. Thus mean plasma betathromboglobulin is higher in groups of patients with disorders known to have thrombotic complications, but the wide range of values, which overlap with normals, prevent the clinical interpretation of the plasma betathromboglobulin level found in any individual patient.