Laboratory Evaluation of Hypercoagulability

Can haematological tests predict cardiovascular risk? The 2005 Kettle Lecture*

The risk of venous or arterial thrombosis is routinely assessed by clinical variables (risk factors) supplemented by measurement of blood lipids and glucose for arterial thrombotic events. Haematological tests that might play a role in risk prediction include haemostatic variables, haematocrit and inflammatory markers (erythrocyte sedimentation rate, plasma viscosity, white cell count). Recent epidemiological studies of these phenotypes and related genotypes are reviewed. For the risk prediction of first venous thrombosis, screening for thrombophilias in 'high-risk' situations does not appear clinically effective or cost-effective; with the possible exception of women considering oral hormone replacement therapy. General screening after a first venous event to predict recurrence (or risk in asymptomatic relatives) does not appear effective; with the possible exception of d-dimer, which requires further study. For risk prediction of first arterial thrombosis, screening adds little to prediction by current clinical risk scores. Screening of persons after a first arterial event, or with atrial fibrillation (e.g. with D-dimer for stroke prediction), requires further study. In conclusion, haematological tests have very limited roles in the prediction of cardiovascular risk, and should only be used according to evidence-based guidelines. The need for management studies is highlighted.

Hematologic disorders and ischemic stroke. A selective review

More than a dozen primary hematologic disorders have been associated with ischemic stroke. Inherited deficiencies of antithrombin III, protein C, and protein S have been linked with stroke in case reports; optimal screening requires functional as well as antigenic assays. Antiphospholipid antibodies and lupus anticoagulants are the most frequently identified acquired states associated with ischemic stroke. Polycythemia vera, sickle cell anemia, sickle-C disease, and essential thrombocythemia are the major disorders of formed blood elements causing stroke. Special, step-wise screening for occult prothrombotic entities in stroke patients is recommended for young persons with stroke of uncertain cause, for those with prior venous thrombosis, for those with a family history of unusual thrombosis, and for those with no other explanation for recurrent stroke. Acquired, perhaps transient, abnormalities of platelets, coagulation inhibition, and fibrinolysis may contribute importantly to brain ischemia in synergy with other mechanisms, but at present these remain ill-defined. The contribution of prothrombotic diatheses to stroke is probably underrecognized and warrants further investigation.

Haemorheologic and fibrinolytic evaluation in obese children and adolescents

The haemorheologic condition was evaluated in 43 obese children and 35 controls. In 18 of the obese children and in 21 controls the euglobulin lysis time (ELT) was also studied. Blood viscosity at 94.5 and at 0.204 s-1 shear rates, plasma viscosity, fibrinogen and erythrocyte filtration time were significantly higher in obese than in control children. No significant differences were observed in haematocrit levels. Triglycerides, non-esterified fatty acids (NEFA), pre-beta-lipoprotein and insulin rates were all significantly higher in obese than in control children. There were no significant differences in glycaemia and in haemoglobin A1 values. ELT, both basal and after stimulation with 1-deamino-8-D-arginine-vasopressin (DDAVP), was significantly higher in the obese than in control children. The haemorheologic disturbances together with alterations of the haemostatic balance and fibrinolysis may be an important risk factor for the development of vascular changes at paediatric age.

Activation of blood platelets and increased plasma fibrinogen and fibronectin in men exposed to infrasounds, acoustic noise and airborne dust in electric steelworks

Concentration of platelet factor 4 (PF4), beta-thromboglobulin (beta TG), fibrinogen (Fg), and fibronectin (Fn) was determined in samples of blood plasma taken from healthy men employed in two electric steelworks in Poland. They had been working at electric arc furnaces and thus particularly exposed to intense infrasounds, acoustic noise and airborne dust during 2 to 15 years for 6-8 hours per day. We found a significant increase in levels of beta TG, Fn, and Fg, but not of PF4, in blood plasma of men exposed to these agents. The beta TG/PF4 ratio, significantly higher in studied groups (p less than 0.001) when compared to control ones, was considerably correlated (r = 0.47, p less than 0.02) with their duration of work. We also found weak correlations between plasma beta TG levels (r = 0.33, p less than 0.05) or concentration of plasma Fn (r = 0.38, p less than 0.02) and time of work under such hazardous conditions.

Internal carotid artery occlusion in association with Crohn's disease

A 38-year-old white male with small bowel Crohn's disease presented with an acute right-sided cerebrovascular accident. He died 36 hr later and postmortem revealed thrombosis over the whole length of an otherwise completely normal left internal carotid artery. Histological examination of the artery revealed no abnormalities and in particular no evidence of arteritis. This brings the total number of such cases reported to three, but this is the first with postmortem data. The occurrence of such an event in a young person with normal carotid arteries and no other risk factors would suggest an association with his Crohn's disease, possibly as a result of a coagulation abnormality.

Platelet function in patients admitted with a diagnosis of myocardial infarction

Platelet function and thromboxane A2 release were measured in 71 patients admitted to a coronary care unit with a provisional diagnosis of acute myocardial infarction (AMI). All measurements were carried out within twenty-four hours of admission. Of these, 35 patients had the diagnosis of AMI confirmed. The remainder (n = 36), who did not have AMI (NMI), were divided into two groups: those (n = 18) with an unequivocal history of previous vascular disease and those without vascular disease (n = 18). Platelet aggregation and thromboxane A2 (TXA2) release were significantly increased in the AMI group when compared with those in the NMI without vascular disease group or a healthy control group with similar age and sex distribution. Aggregation and TXA2 release in the NMI patients with vascular disease were greater than those in controls and did not differ significantly from those in the AMI group. Patients in the AMI or NMI with vascular disease groups who were taking beta-blockers or calcium channel antagonists at the time of admission showed significantly less platelet aggregation than those who were not taking these drugs. Heparin, added in vitro at therapeutic concentrations, induced significantly more aggregation in patients in the AMI and NMI with vascular disease groups than in the NMI without vascular disease group. We conclude that: platelets obtained from patients with AMI are hyperaggregable and release more TXA2; platelets from patients with significant vascular disease are hyperaggregable, even in the absence of AMI, although they are not as hyperaggregable as those from AMI; treatment with nifedipine and beta-blockers protects these patients from platelet hyperaggregability; heparin induces significant aggregation of platelets from patients with AMI and NMI with vascular disease. These observations are of importance in considering the pathogenesis and treatment of AMI and ischemic heart disease.

Fibrinogen mediated activation of platelet aggregation and thromboxane A2 release: pathological implications in vascular disease

The effect of a human fibrinogen preparation on in vitro platelet aggregation was assessed. Platelets were obtained from healthy volunteers. Human fibrinogen induced platelet aggregation in 65% of platelet rich plasma samples and enhanced submaximal platelet aggregation induced by heparin or by several conventional agonists in all samples. Aggregation induced by fibrinogen alone was reversed by the in vitro addition of human albumin. Fibrinogen induced aggregation was associated with the release of the vasoconstrictor, thromboxane A2. Preincubation with indomethacin inhibited both the aggregation and the release of thromboxane A2. Fibrinogen had no effect on in vitro vascular prostaglandin I2 synthesis (rat aortic rings) during a 60 minute incubation. The observed effects of fibrinogen on platelet function may be relevant to clinical conditions in which hyperaggregability of platelets is associated with hyperfibrinogenemia and thrombosis.

Serum crosslinked fibrin (XDP) and fibrinogen/fibrin degradation products (FDP) in disorders associated with activation of the coagulation or fibrinolytic systems

Soluble crosslinked fibrin derivatives (XDP) in serum were determined by enzyme immunoassay utilizing monoclonal antibodies and compared with serum fibrinogen/fibrin degradation products (FDP) assayed by conventional techniques. In healthy subjects and patients with miscellaneous disorders not usually associated with activation of the haemostasis mechanism, mean XDP levels were 45 and 70 ng/ml respectively. However, elevated levels of XDP occurred in conditions commonly associated with intravascular and possibly extravascular activation of the coagulation system. Markedly raised mean XDP values (677-6900 ng/ml) occurred in treated pulmonary embolism, disseminated neoplasia, severe inflammatory disorders and complicated postoperative states, and lesser but significant elevation (mean 150-400 ng/ml) in treated venous thrombosis, uneventful postsurgical states, localized neoplasia, liver disease and symptomatic arterial disease. Levels during initial streptokinase therapy (mean 24 000 ng/ml) fell tenfold as treatment was continued. The degree of XDP elevation over normal values was significantly higher than that of FDP in conditions with a propensity for venous thrombosis (post-operative states, disseminated neoplasia and inflammatory diseases) than in liver disease, localized neoplasia or patients receiving heparin therapy for venous thromboembolism.

Thrombocytopenia and lupus-like anticoagulant in a patient with peripheral vascular disease: response to infusion of prostacyclin

A 46 year old man with intermittent claudication due to severe peripheral vascular disease had a circulating lupus like anticoagulant (LLAC), thrombocytopenia (79 X 109/1), markedly reduced platelet survival and a normal bone marrow. He was treated with intravenous prostacyclin (PGI2) infusions which resulted in improvement of the patient's exercise tolerance and normalisation of his platelet count (300 X 109/1) and platelet aggregation could then be assessed. The platelets were markedly hyperaggregable and generated supranormal quantities of thromboxane A2. A diagnosis of consumptive thrombocytopenia secondary to peripheral vascular disease and platelet hyperaggregability was made. Despite therapy with aspirin and dipyridamole, gradual and progressive reduction in platelet count followed and his exercise tolerance declined over the next three months. Immunoglobulin prepared from the patient's serum did not inhibit vascular PGI2 synthesis in vitro. To our knowledge this is the first reported case of consumptive thrombocytopenia due to severe peripheral vascular disease and platelet hyperaggregability. PGI2 administration caused a transient resolution of these features which was not sustained by aspirin and dipyridamole.

Cardiac and vascular imaging with labeled platelets and leukocytes

The contribution of platelets in atherosclerosis and thrombosis in animal models and in clinical studies has been quantified with 111In-platelet scintigraphy. New in vitro quantitative techniques have been developed using 111In-labeled platelets to determine the number of adherent platelets on deendothelialized surfaces of damaged vessel walls and synthetic vascular grafts. In vivo imaging techniques are semi-quantitative in nature; in these studies 111In radioactivity on thrombotic vessels or graft surfaces of iliac, femoral, or popliteal arteries is compared with contralateral vessels. Background 111In radioactivity in the circulating blood pool of venous and capillary networks and radioactivity in marrow decreases the sensitivity of these techniques. Despite these limitations, the dynamic process of platelet deposition in most of the denuded, atherosclerotic vessels and prostheses in the circulatory system can be recorded. This ongoing thrombosis and embolization has been observed in 5-10-year-old vascular grafts of Teflon and Dacron biomaterials. Currently used platelet function inhibitor drugs, eg, aspirin, Persantine, sulfinpyrazone, and Motrin, have a demonstrable effect on platelet deposition. Slight changes in reduction of platelet deposition on these surfaces due to medical intervention have been observed by noninvasive imaging with 111In-platelets. Subtraction of blood pool radioactivity with 99mTc-labeled autologous red cells and calculation of 111In radioactivity associated with platelet thrombus on vessel walls also have been performed for coronary, carotid, and femoral arteries. Although platelet concentrates are used frequently after open heart surgery (one to six per patient), consumption of platelets in the artificial lung or oxygenator, lysis of platelets during pumping, and suction of blood only recently have been quantified with the use of 111In-labeled platelets. These studies also demonstrated far less trauma to platelets with the use of a membrane rather than a bubble oxygenator. Further reduction in platelet consumption and trauma was observed with the use of prostacyclin, a short-acting drug with significant beneficial effect on platelet thrombus reduction and disaggregation of aggregated platelets. The role of polymorphonuclear leukocytes in inflammation, infection and myocardial infarction, and in vivo evaluation with 111In-leukocyte scintigraphy in animals and humans has been described.(ABSTRACT TRUNCATED AT 400 WORDS)

A new automated technique for platelet aggregation measurement

A Multistat III Centrifugal Analyser (MCA) was used to measure platelet aggregation in vitro. It has a capacity of about 40 samples per h. In the analyser platelet-rich plasma and collagen-reagent were mixed, and the turbidity was measured as a function of time. The results were presented in arbitrary units ( arb . units), i.e. change in turbidity per min X 1000. The estimated 0.95 reference range was 50-95 arb . units, (n = 46) and the coefficient of correlation between MCA results and results obtained by conventional aggregometry ( Fibromat ) was 0.85 (P less than 0.001). The MCA method registered 50-75% reduction of platelet aggregation after intake of low dose acetylsalicylic acid (ASA) (1.2-4.0 mg/kg) during 3 days in 19 subjects. The MCA method is suitable to monitor ASA treatment routinely in order to establish an individual appropriate ASA dose during prophylactic treatment of arterial thromboembolic disease.

Abnormal blood viscosity and haemostasis in long-standing retinal vein occlusion

Blood viscosity and several haemostatic factors were measured in 42 patients with long-standing retinal vein occlusion and 33 control subjects. Blood viscosity, haematocrit, plasma viscosity, fibrinogen, fibrinopeptide A, and beta-thromboglobulin were increased in the 20 subjects with capillary nonperfusion or new vessels, but not in the 22 subjects without these complications. Patients with nonperfusion or new vessels also had a lower platelet count than patients without complications. Increased levels of factor VIII antigen and decreased levels of antithrombin III were found in the retinal vein occlusion group as a whole. These findings suggest that blood viscosity, platelets, and coagulation may be involved in retinal vein occlusion and its vascular complications.