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What can thrombosis lead to?

What can thrombosis lead to?


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I am thinking this question. Thrombosis can result in

  1. organisation of thrombus,
  2. sepsis
  3. thromboembolism,
  4. fibrinoid swelling
  5. adiposity.

I fibrinoid swelling (edema) (4) can occur. Also, I think (3) thromboembolism can occur and also (1) organisation of thrombus.

What can thrombosis result in?


Fibrinoid swelling involves necrosis and swelling so no. Organisation of thrombus refers to some very large space of organising thrombus in different ways - so no, since there is an exact mechanism under. Based on my interpretation of Robbins -book.

The correct answer is 3. thromboembolism. Thromboembolism is a combination of thrombosis and its main complication, embolism.


Thrombosis

formation, development, or presence of a thrombus this can happen whenever the flow of blood in arteries or veins is impeded. Many factors can interfere with normal blood flow: heart failure or physical inactivity may retard circulation generally a change in the shape or inner surface of a vessel wall may impede blood flow, as in atherosclerosis a mass may grow inside the body and exert pressure on a vessel the vessel wall may be injured and roughened by an accident, surgery, a burn, cold, inflammation, or infection or the blood may thicken in reaction to the presence of a foreign serum or snake venom. adj., adj thrombot´ic.

Sometimes a thrombus detaches itself from the wall and is carried along by the bloodstream. Such a clot is called an embolus , and the condition is known as embolism . A thrombus may form in the heart chambers, such as after coronary thrombosis (see below) at the place where the wall of the heart is weakened, or in the dilated atria in a case of mitral stenosis . Because blood normally flows more slowly through the veins than through the arteries, thrombosis is more common in veins than in arteries.

Venous Thrombosis . This occurs most often in the legs or pelvis it may be a complication of phlebitis , result from injury to a vein, or occur with prolonged bed rest. The symptoms&mdasha feeling of heaviness, pain, warmth, or swelling in the affected part, and sometimes chills and fever&mdashdo not necessarily indicate its severity. Immediate medical attention is necessary in any case. Under no circumstances should the affected limb be massaged.

In thrombosis of superficial veins, bed rest with legs elevated and application of heat to the affected area may be all that is necessary. In thrombosis of deep veins, the affected part must be immobilized to prevent the clot from spreading or turning into an embolus , and anticoagulant drugs may be given. With proper treatment, recovery occurs within a short time unless an embolism develops. Practice management guidelines for venous thromboembolism in trauma patients note that a vena cava filter should be considered in patients at high risk who are not candidates for anticoagulants.

Arterial Thrombosis . The main types of arterial thrombosis are related to arteriosclerosis , although thrombosis can also result from infection or from injury to an artery. Arteriosclerosis may be hereditary or may be brought on by diabetes mellitus . Coronary thrombosis, arterial thrombosis in a coronary artery, is a complication of coronary atherosclerosis . A thrombus in one of these arteries will block part of the blood supply to the heart muscle and cause severe myocardial infarction , which is a medical emergency. Cerebral thrombosis is arterial thrombosis in one of the cerebral arteries the thrombus obstructs the supply of blood to the brain and results in stroke syndrome . Causes include hardening of the cerebral arteries, hypertension , complications of syphilis or other infections, dehydration , diabetes mellitus , or a violent injury.

In advanced cases of arteriosclerosis , a thrombus may fill up whatever channel remains through a vessel, completely blocking off circulation and causing gangrene . This occurs most frequently in arteries of the legs and is called peripheral thrombosis. The onset, often sudden, is characterized by either a tingling feeling or numbness and coldness in the limb. Pain is not always present. Immediate treatment with anticoagulants is necessary to discourage clotting. If this is not effective, surgery may be required. This condition is most common in the elderly and in diabetics. There are now methods of treatment that may save the limb, such as surgical removal of a thrombus or embolus, or surgery of blood vessels to remove old, narrowed, or deteriorated vessels and replace them with grafts.


COVID-19: 'I’ve never seen such sticky blood’ says thrombosis expert

COVID-19 leads to blood clots in a significant number of people who have a severe form of the disease. In an interview with Medical News Today, thrombosis expert Prof. Beverley Hunt explains why blood clots are dangerous for those with the new coronavirus.

Share on Pinterest Prof. Beverley Hunt spoke to Medical News Today about blood clots and COVID-19.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub and follow our live updates page for the most recent information on the COVID-19 pandemic.

As news of a SARS-CoV-2, the new coronavirus, traveled across the globe, many experts thought that they would primarily encounter respiratory symptoms.

And little did we expect to be hearing about cardiovascular complications, digestive symptoms, the loss of smell and taste, and the likes of “COVID toe,” one of a collection of skin symptoms that some people with COVID-19 develop.

Blood clots are another complication that has been making headlines. MNT reported on a series of articles in the journal Radiology that suggested that a significant number of people with severe COVID-19 develop life threatening clotting.

But why would a virus that primarily infects the respiratory tract cause blood clots? And how is this putting patients at serious risk?

Prof. Beverley Hunt is the medical director of the British charity Thrombosis UK, as well as chair of the steering group for World Thrombosis Day. She is a professor of thrombosis and hemostasis and works for the United Kingdom’s National Health Service (NHS) in London.

Prof. Hunt told MNT about the biology of blood clotting, her surprise at how the new coronavirus changes the properties of the blood in those with severe disease, and why we should keep moving, even during lockdown, to reduce our risk of thrombosis.

MNT: How do blood clots form, and why are they potentially dangerous?

Prof. Hunt: In 1846, the German pathologist [Rudolf] Virchow described three things that predispose people to venous thrombosis.

They are: changes in the flow of the blood, changes in the stickiness of the blood — although he didn’t use the word “sticky” then — and changes in the blood vessel wall.

Of these, probably the most important one for the average member of the public is flow. Just sitting here for 90 minutes without moving my legs, blood flow crashes. It drops by about 50%.

When you walk, every time your muscles contract, they squeeze the veins and push the blood back up toward the heart.

There isn’t a natural muscular system within the veins, unlike within the arteries. We’re totally dependent on movement to keep the flow going.

This is a major risk factor for hospital patients, for someone who is sick, but also for anyone sitting for long periods of time.

As far as the stickiness is concerned, we are talking about changes in the blood proteins. The commonest cause of these changes is being ill.

If you’re ill, you produce chemical cytokines that tell the liver to make more clotting proteins. Then your blood is full of clotting proteins that make it very sticky and very ready to clot.

The last thing is the lining of the blood vessel. It’s very susceptible to hormones, particularly in people who are ill and people who take hormone replacement therapy. Those cytokines make it much, much more liable to form a clot.

When we come to COVID-19, we know that the new coronavirus can enter the lining of the blood vessels. The new coronavirus behaves in some way like the conductor of the blood clotting orchestra.

MNT: Were you expecting to see such a big problem with blood clots in people with COVID-19?

Prof. Hunt: The issue with COVID-19 is that the blood is incredibly sticky.

We are seeing people in hospital with pneumonia. They are in hospital because they are short of oxygen, and they need extra oxygen. That’s really why they are coming in.

We know that most people who get COVID-19 get better in about 7–10 days, and we have about 5% who develop pneumonia.

Their immune system is reacting very strongly to the pneumonia, and the lungs are full of immune cells that produce cytokines. In turn, these tell the liver to make clotting proteins. The inflammatory mechanism leads to what we call a “prothrombotic state.”

Let me give you an example. The main clotting protein in the blood is fibrinogen. It’s soluble, and you have 2–4 grams per liter in your blood.

The clotting factors switch soluble fibrinogen to insoluble fibrin, and that is the clot.

The level is 2–4 grams per liter in most people. If you are pregnant, or as you get older, the levels get higher. They might go up to 5, 6, or even 7 [grams per liter].

But what are we seeing in COVID-19? We are seeing levels of 10, even 14 grams per liter. I’ve been in this game forever, for decades, and I’ve never seen such sticky blood.

We know that all the other clotting proteins are similarly increased.

Prof. Hunt: I haven’t seen these values before in this many patients. Occasionally, you get a patient who has really high levels. But all of them have these really high levels. That is a major issue.

But we didn’t know that this was going to happen until the patients arrived. The initial reports from China, which we had a little bit of, suggested there were major clotting problems, but they called it something else, and I think they didn’t quite get it right in those early stages.

Now we know that these patients have incredibly sticky blood. This stickiness is causing them to have deep vein thrombosis. And of course, if you have a deep vein thrombosis, bits of it can break off and travel through your body and block some of the blood supply to the lungs.

And because the lungs aren’t working properly in the first place, this really isn’t a good thing in a really sick patient.

So, we are giving all of the COVID-19 patients small doses of blood thinners to reduce the risk. But really, the question is, should we be giving them more?

We know that the doses that we give under normal circumstances have minimal bleed risk. Their advantage is that the risk of blood clots is reduced by 50%. But should we perhaps be giving these patients a little bit more because their blood is so sticky? That’s currently the big research question.

The other thing that we’re seeing, which caught a lot of people out, is blockages in tiny vessels. Normally, if you do imaging of the lungs and you look for blockages in the blood vessels — with a pulmonary embolism, you typically see blockages in a few of the big ones.

What we are also seeing are blockages of tiny little vessels, in what we call subsegmental branches of the pulmonary artery. That’s not really a pulmonary embolism.

When we look at the postmortem reports from Chinese studies and from other studies out there, from the United States, Argentina, and Italy, we know that if there is really profound inflammation in an area, that can lead to thrombosis.

There is so much inflammation in the lung, and then we see small pockets of thrombosis caused by inflammation.

The problem is that — I don’t think we are preventing this with the small doses of blood thinners. This is all about inflammation being so marked that we need to deal with it first. The current clinical trials are looking at reducing the viral load and addressing inflammation.

I think if we had less inflammation, we would see less of the clotting in the tiny blood vessels.


Thromboembolism (Deep Vein Thrombosis and Pulmonary Embolism)

A deep venous thrombosis (DVT) is a blood clot (thrombus) that forms inside deep veins in your legs or pelvis. The clot blocks blood flow and causes pressure to build up in the vein. Part of the clot can break away and move through your bloodstream to your lungs. If the clot blocks one or more of the blood vessels in your lungs, it is called a pulmonary embolism.

DVT is a common problem. Most of these clots occur when blood flow in the veins of the legs is slowed. This is usually as a result of inactivity.

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Inheritance Inheritance

Most cases of essential thrombocythemia are not inherited . Instead, the condition arises from gene mutations that occur after conception ( somatic mutations ). [5]

Less commonly, essential thrombocythemia is inherited in an autosomal dominant pattern. This means that just one copy of the altered gene in each cell is sufficient to cause the condition. When essential thrombocythemia is inherited, it is called familial essential thrombocythemia. [5] In familial cases, an affected person has a 50% (1 in 2) chance of passing on the condition to each of his or her children.


Elevated Factor VIII Levels and the Risk of Thrombosis

From the Hemostasis and Thrombosis Research Center, Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands.

From the Hemostasis and Thrombosis Research Center, Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands.

From the Hemostasis and Thrombosis Research Center, Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands.

In vivo, a delicate balance exists between fibrin formation and fibrinolysis. Reduced blood flow, changes in the vessel wall, and changes in blood composition (hypercoagulability) 1 may all result in a disturbance of this balance, which favors fibrin formation and ultimately may lead to the formation of occlusive thrombi. Venous thromboembolism is the result of clot formation in a vein at sites of reduced blood flow. Arterial thrombosis involves the formation of platelet aggregates at high shear rates at sites of vessel-wall injury.

Classic acquired risk factors for venous thrombosis include trauma, immobilization, pregnancy, surgery, malignancy, and infection. These are all factors that may cause tissue damage, stasis of the blood, or changes in blood composition. Inherited risk factors for venous thrombosis, 2 3 4 5 most of which concern defects in the procoagulant and anticoagulant pathways, account for a substantial proportion of all thrombotic events. Table 1 summarizes prevalences and relative risks of established genetic risk factors. 6 7 8 9

These risk factors include factor V Leiden (resistance to activated protein C [APC]), 9 prothrombin 20210A, 8 and deficiencies in antithrombin, 2 protein C, 3 4 and protein S. 5 10 11 Elevated fibrinogen, 12 antiphospholipid antibodies, 13 and mild hyperhomocysteinemia 14 are examples of laboratory phenotypes associated with venous thrombosis. Some of these phenotypes have also been found to be associated with arterial thrombosis. 15 16 17 Whether this is also true for genetic risk factors such as factor V Leiden or the prothrombin 20210A allele is still uncertain. 18 19 20 21 22 23 24 25 26

Despite growing insight in the pathogenesis of thrombophilia, the cause of many thrombotic episodes remains unknown. Recently, new laboratory phenotypes that are associated with an increased risk of venous thrombosis have been reported . 27 28 29 One of these is an elevated factor VIII level. High factor VIII levels are a common risk factor for venous thrombosis 27 30 31 and may also be associated with the risk of arterial thrombosis in coronary heart disease 32 33 and stroke. 34

The regulation of plasma factor VIII levels is complex. Most factor VIII circulates as a complex with von Willebrand factor (vWF), 35 36 the levels of which are known to be dependent on factors such as blood group 37 38 39 and endothelial stimulation. 40 41 This highly complicates the study of the molecular basis of elevated factor VIII levels.

In the present review, we will summarize the present knowledge on the relation between factor VIII and thrombosis and discuss the possible determinants of elevated factor VIII levels in plasma.

Determinants of Plasma Factor VIII Levels

Genetic Determinants of Plasma Factor VIII Levels

In healthy individuals, family studies have indicated a genetic influence on the level of factor VIII:C. 42 43 Factor VIII levels varied less among twins than among unrelated individuals. Filippi et al 44 have suggested a primary role of X-linked genetic determinants on the basis of the observation of a positive correlation of factor VIII:C levels within groups of male pairs who had identical X alleles. Ørstavik et al 39 found that the variance of factor VIII and vWF:Ag levels was smaller within twin pairs than between these pairs. They estimated that 57% of the total variation in plasma factor VIII levels and 66% of the variation in vWF levels were genetically determined. Most recently, Souto et al 45 reported a heritability of 0.4 for factor VIII levels in the families of the Genetic Analysis of Idiopathic Thrombosis (GAIT) study.

vWF and blood group are important determinants of the factor VIII level in plasma. The blood group non-O is associated with higher vWF and factor VIII levels than is blood group O, 37 38 39 with a mean difference of 31.5 IU/dL for vWF:Ag and 22.4 IU/dL for factor VIII:C. 46 Individuals with blood group AB have the highest vWF levels, whereas AA, AO, BB, and BO genotypes have intermediate levels. 37 47 48 Most of the effect of blood group on the factor VIII level is mediated through vWF. 38 46 Blood group A, B, and H(O) oligosaccharide structures have been identified on vWF, 49 50 which may affect the clearance of vWF and, thus, of the vWF/factor VIII complex. 51 52 Indeed, in patients with hemophilia A, the half-life of infused factor VIII was shorter in patients with blood group O (15.3 hours) than in patients with blood group A (19.7 hours). 53 Both are much longer than the half-life of uncomplexed factor VIII as determined in patients with severe von Willebrand disease (2.8 hours). 54 Interestingly, ABO blood group and plasma vWF level are independent predictors of factor VIII half-life. 53

The high levels of factor VIII in patients with thrombosis persist over time 31 55 and are, in general, not caused by acute-phase reactions. 30 31 56 In addition, O’Donnell et al 55 showed that only 50% of these persistently high factor VIII levels were associated with high vWF:Ag levels, indicating that vWF is not always responsible for high factor VIII plasma levels.

Factor VIII:C levels show a familial clustering, which remains after adjustment for the influence of vWF and blood group. 46 Analysis of familial aggregation of factor VIII levels ≥150 IU/dL in 12 large thrombophilic families 57 identified blood group as the main determinant: 86% of the subjects with factor VIII levels ≥150 IU/dL had blood group non-O. However, after adjustment for blood group and age, factor VIII levels ≥150 IU/dL still aggregated in these families. Others have also observed a high concordance of factor VIII levels between first-degree relatives of patients with thrombosis with high factor VIII levels. 31 58

So far, no variations in the factor VIII or vWF gene that are associated with high factor VIII levels have been identified. No sequence variations were found in the promoter and 3′ terminus of the factor VIII gene in 62 patients with thrombosis with high factor VIII levels. 59 Furthermore, we found no clear association between vWF or factor VIII:Ag levels and polymorphisms in the promoter (−1793 C/G, −1234 C/T, −1185 A/G, and −1051 G/A) and factor VIII binding region (2615 A/G and 2805 G/A) of the vWF gene. 60 However, Keightley et al 61 reported a significant association between vWF levels and the −1234 C/−1185A/−1051G allele in group O blood donors aged >40 years. No association was found between 2 highly informative CA repeats in the factor VIII gene (intron 13 and 22) and plasma levels of factor VIII:Ag. 60 Therefore, other genes may be implicated in the regulation of plasma vWF and factor VIII levels. Finally, factor VIII levels are influenced by sex (higher in women than men) and race (higher in blacks than whites). 61 62

Other Determinants of Plasma Factor VIII Levels

Body mass index (positively correlated with factor VIII levels) and higher levels of glucose (diabetes mellitus), insulin, fibrinogen, and triglycerides are also associated with increased factor VIII levels. 33 63 64 Factor VIII levels increase with age, with an average rise of 5 to 6 IU/dL per decade. 46 63 Oral contraceptives seem to have no effect on factor VIII levels. 63 65

Several stimuli can cause a transient or sustained increase in factor VIII levels. Exercise transiently induces a rise of factor VIII that is probably a result of adrenalin and β2-adrenoreceptor stimulation. 66 67 68 69 70 71 Also, 8-arginine vasopressin and its analogue 1-deamino-8- d -arginine vasopressin enhance plasma vWF and factor VIII levels indirectly or directly via signaling via the V2 receptor. 72 Sustained rises in factor VIII are seen during pregnancy, surgery, chronic inflammation, malignancy, liver disease, hyperthyroidism, intravascular hemolysis, and renal disease. 73 74 In most conditions, there is a concordant increase of factor VIII and vWF:Ag levels.

Determinants of High Factor VIII Levels

Apart from the ABO blood group, no genetic components have been identified that are associated with high plasma factor VIII levels.

Possible determinants of elevated factor VIII levels are summarized in Table 2 . The main determinant is an elevated vWF level, which is under the control of autosomal genes. The ABO blood group, which is the best-characterized modifier of the plasma vWF level, explains ≈30% of the genetically determined variation in vWF levels. 39 In humans, the majority of genetic factors regulating vWF remain to be determined. Candidate genes include a variety of genes coding for proteins involved in the biosynthesis and clearance of vWF. 75 In mice, 2 modifier loci of vWF have been identified, 1 of which concerns an N-acetylgalactosaminyltransferase gene. 76 77 Other important determinants of vWF level are age, acute phase, stress, and endothelial dysfunction.

Twenty-six percent of the subjects with factor VIII:Ag levels ≥150 IU/dL have vWF levels <150 IU/dL, 60 and only 50% of patients with thrombosis with sustained factor VIII:C levels ≥150 IU/dL also have persistent high vWF:Ag levels. 55 This illustrates that there are determinants of elevated factor VIII levels that do not act via vWF. Differences in genetically defined binding affinities of vWF and factor VIII may result in variations of plasma factor VIII levels that are not explained by variations in the vWF level. Differences in the stability of unbound factor VIII, which normally has a very short half-life, may also play a role. 54

Factors V and VIII are related proteins and share common biosynthetic pathways, as reflected by recent studies of Nichols and colleagues 78 79 and Neerman-Arbez et al 80 in combined factor V and VIII deficiencies. The gene coding for the ER-Golgli Intermediate Compartment protein ERGIC-53 was shown to have quantitative effects on factor VIII levels. Factor V:Ag levels are correlated to some extent with plasma factor VIII:Ag levels, 81 suggesting that common posttranslational modifications may explain part of the large variation in plasma factor V and VIII levels.

In all studies investigating the effect of high factor VIII on thrombosis, subjects with malignancy or chronic diseases were excluded, which makes the contribution of inflammation to high factor VIII levels in these groups small. Most likely, high factor VIII levels are the result of a combination of genetic and acquired factors.

Elevated Factor VIII Levels and Thrombosis

Arterial Thrombosis

Low Factor VIII Levels

In 1989, a study by Rosendaal et al 82 reported that low factor VIII levels protect against ischemic heart disease. Mortality due to ischemic heart disease is much lower in patients with hemophilia A than in the general male population, 82 83 which may suggest that factor VIII is involved in the pathogenesis of arterial thrombosis. Also vWF, the main determinant of the factor VIII level in plasma, may play a role in the pathogenesis of atherothrombosis. Autopsy findings from patients with severe von Willebrand disease have shown extensive atherosclerosis but no occlusive arterial thrombi, 84 85 which suggests that even very low vWF levels may not fully protect against the development of atherosclerotic lesions. Similarly, dogs with severe von Willebrand disease and undetectable vWF levels did not develop acute occlusive thrombi in atherosclerotic arteries, 86 suggesting that vWF supports the progression of microthrombi into occlusive thrombosis.

High Factor VIII Levels

The first reports on a possible association between factor VIII and coronary artery disease date from the early 1960s. 87 In the same period, blood group non-O and high factor VIII–related antigen (vWF) were identified as candidate risk factors for atherothrombotic disease. 88 89 90 91 Later, the clarification of the mutual relationships between blood group, vWF, and factor VIII allowed a better appreciation of these early findings. Since then, several case-control studies have reported the association of factor VIII with coronary heart disease. 91A

Several (but not all) large prospective studies in healthy individuals report an association between elevated factor VIII:C and vWF levels and the incidence of ischemic heart disease, especially fatal events (Table 3 ). After correction for other cardiovascular risk factors, this association was eliminated in the Atherosclerosis Risk in Communities (ARIC) Study 33 but not in the Caerphilly Heart Study, 94 leaving the possibility open that factor VIII:C and vWF have an effect on cardiovascular risk. More recently, the prospective Cardiovascular Health Study showed that elevated factor VIII levels were associated with cardiovascular disease and mortality in elderly men also. 92 vWF levels were also predictive for cardiovascular events in patients with stable angina pectoris. 93

Regarding the risk of stroke, the ARIC Study showed that per SD increase in factor VIII and in vWF, the risk increased 1.34-fold (95% CI 1.2 to 1.5) and 1.36-fold (95% CI 1.2 to 1.5), respectively. 34 In addition, elevated vWF levels were associated with mortality in patients who had previously suffered from stroke. 95

From these data and many similar data in the literature, it can be concluded that vWF and factor VIII levels are associated with a moderate increased risk of arterial thrombosis with similar risk estimates for both factors. In the Caerphilly Heart Study, 95 8.9% of the patients with ischemic heart disease had factor VIII levels exceeding 123 IU/dL, with an associated relative risk of 1.9. This results in a population-attributable risk of 4% ie, 4% of all arterial thrombotic events would have been prevented if this risk factor was eliminated, provided that the relation between factor VIII and arterial thrombosis is causal. 96

Potential Mechanisms for the Relation of High Factor VIII Levels to Arterial Thrombosis

Several studies have addressed whether vWF or factor VIII is the causative factor in arterial thrombogenesis and whether the risk of high vWF and factor VIII is blood group dependent. Meade et al 32 found that factor VIII remained associated with ischemic heart disease after adjustment for blood group, without taking vWF into account. Also in the Hoorn study (Jager et al 97 ), high vWF levels were associated with cardiovascular mortality independent of blood group in diabetic and nondiabetic subjects. When vWF and factor VIII are mutually adjusted for, neither of the 2 remained associated with coronary disease. 95 Therefore, it is likely that factor VIII and vWF increase the risk of arterial thrombosis, independent of blood group.

The ARIC Study demonstrated strong associations of factor VIII and vWF with risk factors for atherosclerosis, 63 such as hypertension, diabetes, body mass index, and triglycerides. Some of these factors are known to be associated with perturbed endothelial and vascular inflammation. 98 99 High shear forces, such as those that occur in stenosed vessels, increase vWF secretion by vascular endothelium 41 and, thus, will stimulate platelet adhesion and aggregation at the site of damaged arterial walls, which may lead to thrombus formation. 100 This may explain why elevated factor VIII and vWF levels are associated with stroke in subjects with presumed large-vessel disease, 97 which is mainly the result of atherothromboembolism. 101 At the same time, high factor VIII levels may stimulate the formation of thrombin and, thus, result in increased platelet activation and fibrin formation, processes that may contribute to the development of large occlusive thrombi from the microthrombi initially formed on the damaged endothelium.

Is there a causal relationship between high factor VIII and vWF levels and arterial thrombosis? Atherosclerosis itself could have affected the clotting factor levels by chronic inflammatory responses and elevated factor VIII, or vWF levels may reflect the inflammation and progression of atherosclerosis. 93 However, such a model cannot explain the association between blood group (which is genetically determined) and cardiovascular disease, 32 102 103 unless blood group does not act via vWF. Furthermore, the effect of factor VIII and vWF on arterial thrombosis was not attenuated after adjustment for age and other classical risk factors, such as hypertension, body mass index, cholesterol, and baseline ischemic heart disease. 95 Even C-reactive protein, a strong marker of inflammation, did not clearly affect the risk associated with high vWF levels. 97 The lack of association between factor VIII and vWF levels with carotid intima-media thickness among subjects with prevalent cardiovascular disease is another argument against elevated factor VIII/vWF being simply the consequence of atherosclerosis. 104 In conclusion, it seems likely that high factor VIII and vWF levels have independent roles in increasing the risk of arterial thrombosis. The latter hypothesis is supported by the low cardiovascular mortality in patients with hemophilia A. 82

Venous Thrombosis

High Factor VIII Levels

In 1969, Jick et al 105 reported that blood group non-O is associated with an increased risk of venous thrombosis. Today, we know that individuals with blood group non-O have higher levels of vWF and factor VIII than do those with blood group O. 37 38 39 91 106 In a large population-based case-control study on venous thrombosis (the Leiden Thrombophilia Study), blood group non-O, vWF:Ag, and factor VIII:C levels were all associated with an increased risk for venous thrombosis by univariate analysis. 27 In multivariate analysis, factor VIII:C levels remained a risk factor for thrombosis, but the effect of blood group and vWF:Ag on thrombosis largely disappeared. This suggests that factor VIII is an independent risk factor for venous thrombosis and that vWF and blood group are only risk factors insofar as they affect the factor VIII level. 27 Table 4 shows the risk of thrombosis for approximate quartiles of factor VIII:C. There is a clear dose-dependent relation between factor VIII levels and risk of thrombosis. The adjusted relative risk for factor VIII:C levels ≥150 IU/dL compared with levels <100 IU/dL is 4.8 (95% CI 2.3 to 10.0). Compared with subjects with levels <150 IU/dL, subjects with levels ≥150 IU/dL have a 3-fold increased risk. Furthermore, each increase in the factor VIII:C level of 10 IU/dL is associated with a 10% increase in the risk of a first thrombotic event. 31 56

The association between high factor VIII:C levels and venous thrombosis has been confirmed in several independent studies. 30 31 107 Also, high factor VIII antigen (factor VIII:Ag) levels are associated with venous thrombosis in the Leiden Thrombophilia Study. The relative risk for venous thrombosis of factor VIII:Ag levels ≥150 IU/dL is 5.3 (95% CI 2.7 to 10.1) compared with levels <100 IU/dL, 108 which is very similar to the risk previously reported for factor VIII activity levels ≥150 IU/dL. 27 After excluding all subjects with factor V Leiden, prothrombin 20210A mutation, and a deficiency of protein C, protein S, or antithrombin (defined as previously described 6 ) or of lupus anticoagulant, the thrombosis risk for factor VIII:Ag levels ≥150 IU/dL is still increased (odds ratio 4.7, 95% CI 2.3 to 9.3).

The prevalence of elevated factor VIII levels is high: 25% of patients with a first episode of deep-vein thrombosis and 11% of healthy control subjects have factor VIII levels ≥150 IU/dL. 27 The estimated population-attributable risk for factor VIII levels ≥150 IU/dL is ≈16%. With a causal relationship between high factor VIII and venous thrombosis presumed, 16% of all deep-vein thromboses in the population are the result of high factor VIII levels, indicating that this is an important prothrombotic risk factor.

There are several studies reporting that high levels of factor VIII are associated with an increased risk of recurrences of thrombosis. Kraaijenhagen et al 31 found factor VIII levels ≥150 IU/dL in 57% of patients with recurrent venous thrombosis. Kyrle et al 109 followed 360 patients with venous thromboembolism and found a recurrence in 27% of patients with factor VIII levels >234% (90th percentile in the patient group!) and in 9% of patients without elevated factor VIII levels.

Interaction of Factor VIII and Other Risk Factors for Thrombosis

In thrombophilic families in which protein C deficiency and factor V Leiden were both present, a history of thrombosis was present in 31% of individuals with protein C deficiency, in 13% of individuals with factor V Leiden, and in 73% of subjects with the combined defects. 110 In addition, selected patients from thrombophilic families with factor V Leiden have, on average, a lower median age at the first thrombotic event (29 years) than “unselected” consecutive thrombotic patients with factor V Leiden (43 years). 111 These observations suggested that venous thromboembolism is a multicausal disease and that several risk factors for thrombosis need to accumulate in the individual before a threshold is passed and a thrombotic event will occur. 112

Recently, the influence of high factor VIII levels on the occurrence of venous thrombosis was investigated among the relatives of symptomatic factor V Leiden carriers. 113 Compared with their relatives with either high factor VIII or factor V Leiden, first-degree relatives with the combination of a factor VIII level ≥150 IU/dL and factor V Leiden had an increased rate of venous thrombosis. This means that factor VIII levels ≥150 IU/dL will contribute to the risk of venous thrombosis of factor V Leiden carriers.

Factor VIII levels >150 IU/dL also affected the thrombotic risk of oral contraceptive users. In women with factor VIII:C ≥150 IU/dL, the risk associated with oral contraceptive use was 10.3 (95% Cl 3.7 to 28.9), which is 2-fold higher than the risk among nonusers with factor VIII:C <150 IU/dL (odds ratio 5.3, 95% Cl 1.8 to 15.5). 114 There is no indication that the simultaneous presence of high factor VIII and oral contraceptive use will result in an excess of thrombotic events (interaction).

Relationship Between High Factor VIII and Venous Thrombosis

The precise role of high factor VIII levels in defining venous thrombotic risk is still unknown. After its activation by thrombin, factor VIIIa dissociates from vWF to form a complex with factor IXa, which will result in marked acceleration of the activation of factor X. 115 Activated factor X then converts prothrombin into thrombin, which in turn converts soluble fibrinogen into insoluble fibrin. It is possible that high factor VIII levels just increase the rate of thrombin and fibrin formation (in plasma, there is a large molar excess of factor IX over factor VIII).

Another possibility is that high factor VIII levels influence thrombotic risk via an effect on the APC sensitivity ratio (APCR). It has been shown that (in the absence of factor V Leiden) the thrombosis risk for the lowest quartile of normalized APCR (<0.92) is 4.4-fold higher than that for the highest quartile (≥1.05). 116 For these measurements, “first-generation” APC-resistant tests were used (no dilution of the sample with factor V–deficient plasma). This explains the finding that high factor VIII levels are associated with a reduced sensitivity for APC in the absence of factor V Leiden (see Figure ). 107 117 118 After adjustment for factor VIII levels, the thrombosis risk associated with a normalized APCR <0.92 fell from 4.4- to 2.5-fold, indicating that factor VIII has a strong confounding effect on the thrombosis risk of a low APC ratio. Vice versa, it is also possible that high factor VIII exerts a thrombotic risk through the associated decreased responsiveness to APC. In all subjects of the Leiden Thrombophilia Study who do not have the factor V Leiden mutation, the thrombosis risk associated with factor VIII levels ≥150 IU/dL is 4.8 (95% CI 3.1 to 7.5) compared with the risk associated with levels <100 IU/dL (Table 5 ). Entering normalized APCR as a continuous variable lowered the thrombosis risk of factor VIII levels ≥150 IU/dL by 50%, to 2.7 (95% CI 1.6 to 4.7). Adjustment for age, blood group, and vWF did not change this risk estimate (odds ratio 2.4, 95% CI 1.2 to 5.2). Although high factor VIII remained an independent risk factor for thrombosis, these data show that adjustment for the APCR leads to attenuation of the risk of thrombosis. Therefore, it is possible that the risk of high factor VIII is at least partly mediated through an acquired APC resistance via a pathway that is independent of vWF and blood group.

Should We Screen Patients With Thrombosis for High Factor VIII Levels?

An important question is whether we should screen patients with thrombosis for high factor VIII levels. High levels of factor VIII are a risk factor for a first thrombotic event, but high levels also seem to increase the risk of recurrences, 109 which may indicate that sustained anticoagulant treatment is needed in these patients. When high factor VIII is included in a thrombophilia workup, we must make sure that testing for high factor VIII is reliable and that the individual’s risk of thrombosis is estimated correctly.

First, the assay of factor VIII itself may lead to considerable variation. 119 Together with vWF:Ag, factor VIII:C showed the highest between-duplicate (5.6%) and between-day (15%) coefficients of variation. Most often, factor VIII is measured as factor VIII:C by using modifications of the activated partial thromboplastin time (1-stage assay). This 1-stage assay has the advantage of simplicity but can give falsely high results that are due to activation of the coagulation system during blood collection procedures and/or storage. Factor VIII:Ag can be measured by ELISA. 108 The advantage of an ELISA (if properly designed) over the 1-stage assay is that it is not susceptible to activation of the coagulation system. The disadvantage of the ELISA is that it is more complicated to perform.

Furthermore, there is a large intraindividual variation in factor VIII levels, and finally, there is the important question of how we should interpret the result of a factor VIII measurement in terms of risk of a first thrombotic event and risk of recurrences. Should we use cutoff values? How should we handle in this context information on the presence of disease(s) that have been reported to be associated with high factor VIII levels (eg, malignancies)? Should we combine the result of the factor VIII measurement with information on vWF levels and blood group? Should we restrict the analysis to carriers of other risk factors of thrombosis? Still another problem is the timing of factor VIII measurement: during the acute thrombotic event, factor VIII levels may be elevated because of an acute phase reaction, and a reliable baseline value might not be obtained before several months. Taken together, there are still too many questions to be answered to recommend factor VIII measurement in routine thrombophilia screening.

Conclusions

High levels of factor VIII are a risk factor for thrombosis, with a greater impact on venous than on arterial thrombosis. This risk is dose dependent for venous thrombosis, and factor VIII levels ≥150 IU/dL account for 16% of all venous thrombotic events, whereas factor VIII levels>123 IU/dL explain 4% of all arterial events. High factor VIII levels may increase the risk of venous thrombosis via enhanced thrombin formation and/or through the induction of acquired APC resistance. The relationship between factor VIII and arterial thrombosis may be based on the combination of increased thrombin formation and increased platelet adhesion/aggregation, induced by vWF, at sites of arterial wall damage.

The molecular basis of high factor VIII levels is only partially known and consists of genetic and acquired factors. Blood group, acting through vWF levels, is an important genetic factor that explains ≈30% of the variation in factor VIII levels. Attempts to find other genetic loci associated with high vWF and factor VIII levels have failed until now. It is likely that the largest part of high factor VIII levels is caused by a rise in vWF levels, which points to an increased synthesis or decreased clearance of the vWF–factor VIII complex. However, a substantial percentage of high factor VIII levels is not completely vWF-mediated and may point to genetically defined differences in the affinity of factor VIII for vWF.

Figure 1. Factor VIII:C and normalized APCR in 337 patients and 455 control subjects who do not have the factor V Leiden mutation. 116 The figure shows a clear inverse correlation between factor VIII:C levels and the normalized APCR.

Table 1. Genetic Risk Factors for Venous Thrombosis: Prevalence and Relative Risk

Data are from the Leiden Thrombophilia Study which involved 474 consecutive patients with a first deep vein thrombosis and 474 healthy control subjects. 6 7 8 Protein S deficiency was not associated with increased thrombotic risk in this case-control study, which contrasts with previous findings in family studies. 10 11

Table 2. Possible Determinants of High Factor VIII Levels

Table 3. Prospective Studies on Relationship Between Factor VIII and vWF Levels and Risk of Coronary Heart Disease

NPHS indicates Northwick Park Heart Study.

1 Odds Ratio (OR) per 1 SD increase in factor VIII or vWF.

3 Adjusted for blood group.

Table 4. Relative Risk of Thrombosis for Categories of Factor VIII:C Levels

Data are from Koster et al. 27

1 Adjusted for blood group and vWF:Ag levels.

Table 5. ORs for Factor VIII:C Levels, Unadjusted and Adjusted for APCR (Without Factor V Leiden)

1 Adjusted for activated partial thrombopastin time–based normalized APCR.


Thrombosis

formation, development, or presence of a thrombus this can happen whenever the flow of blood in arteries or veins is impeded. Many factors can interfere with normal blood flow: heart failure or physical inactivity may retard circulation generally a change in the shape or inner surface of a vessel wall may impede blood flow, as in atherosclerosis a mass may grow inside the body and exert pressure on a vessel the vessel wall may be injured and roughened by an accident, surgery, a burn, cold, inflammation, or infection or the blood may thicken in reaction to the presence of a foreign serum or snake venom. adj., adj thrombot´ic.

Sometimes a thrombus detaches itself from the wall and is carried along by the bloodstream. Such a clot is called an embolus , and the condition is known as embolism . A thrombus may form in the heart chambers, such as after coronary thrombosis (see below) at the place where the wall of the heart is weakened, or in the dilated atria in a case of mitral stenosis . Because blood normally flows more slowly through the veins than through the arteries, thrombosis is more common in veins than in arteries.

Venous Thrombosis . This occurs most often in the legs or pelvis it may be a complication of phlebitis , result from injury to a vein, or occur with prolonged bed rest. The symptoms&mdasha feeling of heaviness, pain, warmth, or swelling in the affected part, and sometimes chills and fever&mdashdo not necessarily indicate its severity. Immediate medical attention is necessary in any case. Under no circumstances should the affected limb be massaged.

In thrombosis of superficial veins, bed rest with legs elevated and application of heat to the affected area may be all that is necessary. In thrombosis of deep veins, the affected part must be immobilized to prevent the clot from spreading or turning into an embolus , and anticoagulant drugs may be given. With proper treatment, recovery occurs within a short time unless an embolism develops. Practice management guidelines for venous thromboembolism in trauma patients note that a vena cava filter should be considered in patients at high risk who are not candidates for anticoagulants.

Arterial Thrombosis . The main types of arterial thrombosis are related to arteriosclerosis , although thrombosis can also result from infection or from injury to an artery. Arteriosclerosis may be hereditary or may be brought on by diabetes mellitus . Coronary thrombosis, arterial thrombosis in a coronary artery, is a complication of coronary atherosclerosis . A thrombus in one of these arteries will block part of the blood supply to the heart muscle and cause severe myocardial infarction , which is a medical emergency. Cerebral thrombosis is arterial thrombosis in one of the cerebral arteries the thrombus obstructs the supply of blood to the brain and results in stroke syndrome . Causes include hardening of the cerebral arteries, hypertension , complications of syphilis or other infections, dehydration , diabetes mellitus , or a violent injury.

In advanced cases of arteriosclerosis , a thrombus may fill up whatever channel remains through a vessel, completely blocking off circulation and causing gangrene . This occurs most frequently in arteries of the legs and is called peripheral thrombosis. The onset, often sudden, is characterized by either a tingling feeling or numbness and coldness in the limb. Pain is not always present. Immediate treatment with anticoagulants is necessary to discourage clotting. If this is not effective, surgery may be required. This condition is most common in the elderly and in diabetics. There are now methods of treatment that may save the limb, such as surgical removal of a thrombus or embolus, or surgery of blood vessels to remove old, narrowed, or deteriorated vessels and replace them with grafts.


Physical inactivity increases risk of thrombosis

Women with poor physical fitness display significantly higher platelet activation than women with average to very good fitness. That is the major finding of a study of 62 young women, conducted by the research groups of Ivo Volf (MedUni Vienna Institute for Physiology) and Rochus Pokan (University of Vienna Institute for Sports Sciences) and sponsored by the Austrian Heart Foundation. Platelet (thrombocyte) activation can lead to the formation of potentially life-threatening blood clots. These blood clots can block blood vessels (thrombosis) and cut off the blood supply to organs.

The findings from this study have been published in the leading international journal Medicine & Science in Sports & Exercise. At the same time, however, the researchers were able to show that this platelet function normalized very quickly as a result of increased fitness -- this was achieved by endurance training (running for a maximum of 40 minutes) just three times a week over the two-month period.

Cardiovascular diseases and their acute forms of heart attack and stroke are the commonest causes of death throughout the world. These diseases develop over several decades and are favoured by several risk factors that have a negative impact upon the function of various target cells. Activation of blood platelets can cause clumping of these cells and hence the formation of a thrombus (clot), which impedes blood flow. Activated platelets are also involved in inflammatory processes. For this reason, excessive platelet activation can also encourage inflammatory processes, which can bring about a rapid deterioration of the clinical picture in patients with cardiovascular diseases.

However, the results of the study show that even moderate training can bring about significant improvements within a comparatively short time -- so that platelet activation parameters approximate to those found in the two fitter groups of volunteers.

Better assessment of the preventive effect of training

The study's lead author Stefan Heber: "Latently activated platelets release a number of mediators that can encourage the development of atherosclerotic vascular changes. If poor physical fitness is accompanied by a higher level of platelet activation, one can conclude that it also has an influence upon the early stages of this pathogenesis. The training effects we've found here are consistent with epidemiological data, according to which fit people have an approximately 40% lower risk of cardiovascular events than those who were physically inactive."

These findings could therefore be very helpful in assessing the preventive effect of different training methods and/or intensities: "Platelet-based studies could open up significant new possibilities for the direct and short-term comparison of the effectiveness of various training programmes in the field of cardiovascular disease prevention," says research group leader Ivo Volf.


The influence of thyroid function on the coagulation system and its clinical consequences

Several studies indicate that low plasma levels of thyroid hormone shift the hemostatic system towards a hypocoagulable and hyperfibrinolytic state, whereas high levels of thyroid hormone lead to more coagulation and less fibrinolysis. Low levels of thyroid hormone thereby seem to lead to an increased bleeding risk, whereas high levels, by contrast, increase the risk of venous thromboembolism. Hypothyroidism leads to a higher incidence of acquired von Willebrand's syndrome and with increasing levels of free thyroxine, levels of fibrinogen, factor VIII and von Willebrand factor, amongst others, increase gradually, to the extent that they may lead to symptomatic venous thromboembolism in patients with hyperthyroidism. Here, we discuss the literature on the effect of thyroid hormone on the hemostatic system and the associated risk of bleeding and venous thromboembolism. Patients with hypothyroidism are at increased risk of developing bleeding complications, which could be relevant in patients undergoing invasive procedures. Furthermore, physicians should be aware of the possibility of hyperthyroidism as an underlying risk factor for venous thromboembolism, especially in unexplained cases. Clinical studies are needed to further investigate the significance for general practice of these findings. Besides the effects of hyperthyroidism on venous thromboembolism, its effects on embolism secondary to atrial fibrillation are described.

Keywords: blood coagulation fibrinolysis hemorrhage hyperthyroidism hypothyroidism venous thrombosis.


Conclusion

Thrombosis has been well-recognized as the leading cause of death in PNH. Preventing thrombosis in this disease and effectively treating thrombosis early on in its presentation are paramount. Appreciating the high frequency of thrombosis in PNH should lead one to thorough, and possibly multiple, investigations to exclude thrombosis. A patient presenting with thrombosis should be considered for screening for PNH if they fall into one of the 4 categories described.

The tendency toward thrombosis in patients with PNH is multifactorial in etiology, involving the absence of GPI-anchored complement inhibitors on the surfaces of circulating platelets, the high levels of intravascular free plasma hemoglobin with the consequent scavenging of NO, fibrinolytic defects, and the pro-inflammatory effects of C5a. The relative importance of each factor is not yet known but the integration between the 2 major host protection systems, coagulation and innate immunity, is obvious. The majority of the mechanisms relate to complement dysfunction and its consequences. Therefore eculizumab, which addresses these mechanisms, resulting in the reduction of thrombosis risk, has now become an important part of the management of this most feared complication. Because thrombosis is the leading cause of death, the impact of eculizumab on thrombosis largely explains the improved survival seen with eculizumab therapy.