ABC
of Blood Clot Formation (Thrombosis)
The term thrombosis describes the
formation of a blood clot in a blood vessel. The blood vessel can be a vein
(venous system) or an artery (arterial system). The symptoms that occur with a
clot depend on where the clot occurs, the size of the clot, and whether the
clot breaks off and travels to another part of the body (a process called
embolization). For example, a blood clot in the leg can break off and travel to
the lungs (called a pulmonary embolism) or travel to the brain (called an
embolic stroke).
Clots in the veins mainly occur in the
extremities, but they can also occur in the veins of internal organs such as
the liver, spleen, or intestines. The most common types of clots in the veins
are deep vein thrombosis (DVT) and pulmonary embolism
(PE). Clots in the arteries can also affect a variety of organs
including the brain (stroke), heart (myocardial infarction), or intestines
(abdominal angina).
Thrombophilia is a term used to describe
a group of conditions in which there is an increased tendency, often
repeated and over an extended period of time, for excessive clotting. Inherited
or acquired abnormalities of coagulation can increase an individual’s risk of
developing a clot. These conditions are prothrombotic
(ie, they promote clot formation) and are commonly known as clotting
disorders or thrombophilia. For more detailed information on
clotting disorders, According to the US Centers for Disease Control and
Prevention (CDC),1 between 5% and 8% of the US population has a
clotting disorder. Inherited clotting disorders such as deficiencies in
antithrombin, protein C or protein S lead to a lifelong increased risk of
clots. Identifying an underlying clotting condition clearly has important
implications for an individual’s life and medical care.
The risk of blood clots is higher in
individuals who have several risk factors for clotting— for example, a person
with an inherited clotting condition Factor V Leiden [FVL], protein S deficiency, protein C deficiency, or antithrombin deficiency) who also has other
risk factors such as pregnancy, oral contraceptive use, or high levels of
homocysteine or factor VIII is at a higher risk for developing a clot than an
individual with an isolated or single risk factor.
The precise number of individuals
affected by clotting in the veins (venous thrombosis) is unknown. According to
the CDC, 300,000 to 600,000 people per year experience DVT or PE.
Of those who experience a DVT,
nearly one third develop postthrombotic syndrome. The symptoms of this
chronic disabling condition include swelling, pain, discoloration, and scaling
of the affected limb. For some individuals DVT becomes a chronic illness— about
30% of people who have a DVT are at risk of experiencing another clotting
episode. It is important to note that many episodes of DVT are
preventable and treatable if diagnosed accurately and early.
An estimated 60,000 – 100,000 Americans
die of DVT/PE each year.1 Because fewer than 50% of the people
with PE have symptoms, some studies suggest that the actual numbers of affected
individuals may be much higher.2 Estimates of the number of
people with PE are less reliable than those for DVT because many
patients with PE are not diagnosed.
Incidence of Blood Clots in Pediatric
Populations
Although blood clots are more common in
adults, they also can occur in children. The annual incidence in pediatric
populations is 0.07 to 0.14 per 10,000 children, or 5.3 per 10,000 pediatric
hospital admissions, and 24 per 10,000 neonatal intensive care unit admissions.
Newborns and babies younger than 1 year are at greatest risk for childhood
clots. Children in neonatal and pediatric intensive care units and those with
cancers are particularly at high risk. A second peak occurs in adolescence.
Teenage girls have twice the rate of clots as teenage boys. This difference is
related to the use of oral contraceptives and pregnancy. Even in the presence
of inherited or acquired clotting risk factors, children are less likely than
adults to develop clots because they have generally healthy blood vessels.
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