What Causes Excessive Blood Clotting?
To understand what causes excessive blood clotting,
it helps to understand the bodys normal blood clotting process.
Normally, blood clots form to seal small cuts or
breaks on blood vessel walls and stop bleeding. After the bleeding has stopped
and healing has occurred, the body breaks down and removes the clots.
Blood clotting is a complex process, but it mainly
involves:
- The inner layer of the cells lining the blood
vessels. These cells play a major role in causing blood clots to form.
- Clotting factors. These proteins help create a
network of fibrinanother type of protein. Fibrin acts as glue to hold a
blood clot together.
- Platelets (PLATE-lets). These small blood cell
fragments can stick together to form a clot.
Excessive blood clotting may occur if the
bodys clotting process is altered or wrongly triggered. Blood clots can
form in or travel to the arteries or veins in the brain, heart, kidneys, lungs,
and limbs.
Certain diseases and conditions, genetic mutations,
medicines, or other factors can cause excessive blood clotting.
Diseases and Conditions
A number of diseases and conditions can cause the
blood to clot too much or prevent blood clots from dissolving properly. Certain
diseases and conditions are more likely to cause clots to form in certain areas
of the body.
Antiphospholipid Antibody Syndrome
This condition, also called
APS, is an autoimmune disorder. If you have
APS, your body makes antibodies (proteins) that attack phospholipids
(fos-fo-LIP-ids)a type of fat. Phospholipids are found in all living
cells and cell membranes, including blood cells and the lining of blood
vessels.
In APS, the antibodies trigger blood clots to form
in the bodys arteries and veinsthe vessels that carry blood to your
heart and body. These blood clots can lead to a number of health problems,
including frequent miscarriages.
APS is more common in women and people who have
other autoimmune or rheumatic disorders, such as
lupus.
Bone Marrow Disorders
Some bone marrow disorders can cause your body to
make too many blood cells that can lead to blood clots. Examples of such
disorders include
polycythemia
vera (POL-e-si-THE-me-ah VE-ra), or PV, and
thrombocythemia
(THROM-bo-si-THE-me-ah).
PV is a rare blood disease in which your body makes
too many red blood cells. These extra red blood cells make your blood thicker
than normal. This slows the flow of blood through your small blood vessels and
can lead to blood clots.
Thrombocythemia is a condition in which your body
makes too many platelets. The platelets can stick together to form blood
clots.
Thrombotic Thrombocytopenic Purpura and
Disseminated Intravascular Coagulation
Two rare, but serious conditions that can cause
blood clots are
thrombotic
thrombocytopenic purpura (throm-BOT-ik throm-bo-cy-toe-PEE-nick
PURR-purr-ah), or TTP, and disseminated intravascular clotting, or DIC.
TTP causes blood clots to form in the body's small
blood vessels, including vessels in the brains, kidneys, and heart.
DIC is a rare complication of pregnancy, severe
infections, or severe trauma. DIC causes tiny blood clots to form suddenly
throughout the body.
Problems With Blood Clot Breakdown
After a blood clot has done its job, the body
normally breaks down the fibrin that holds the clot together.
Several rare genetic and acquired conditions affect
the fibrin network that holds blood clots together. Thus, the clots don't break
down properly and they remain in the body longer than needed.
In one condition, for example, the body's fibrin is
abnormal and resists being broken down. In another condition, the body has a
decreased amount of plasmin. This protein is needed to break down fibrin.
Excessive Blood Clotting That Mainly Affects the
Heart and Brain
Any condition that damages the smooth inner surface
of the blood vessels can trigger blood clotting. Many of these conditions are
acquired. However, some genetic problems also can damage the blood vessel
walls.
Certain diseases, conditions, or factors may trigger
excessive blood clotting mainly in the arteries and veins of the heart and
brain.
Atherosclerosis.
Atherosclerosis
is a disease in which a fatty material called plaque (plak) builds up on the
insides of your arteries. Over time, the plaque may crack. Platelets clump
together to form blood clots where the cracks are. Atherosclerosis is a major
case of damage to the blood vessel walls.
Vasculitis.
Vasculitis
(vas-kyu-LI-tis) is a disorder that causes the body's blood vessels to become
inflamed. Platelets may stick where the arteries are damaged, and blood clots
can form. Vasculitis also is a major cause of damage to the blood vessel
walls.
Diabetes.
Diabetes increases the risk for plaque buildup in the
arteries. Nearly 80 percent of people who have diabetes die from dangerous
blood clots. (Seventy-five percent of these deaths are due to complications
with the heart and blood vessels.)
Heart failure. Heart
failure is a condition in which the heart is damaged or weakened and can't
pump enough blood to meet the body's needs. This condition slows blood flow,
which can cause blood clots to form.
Atrial fibrillation.
Atrial
fibrillation (A-tre-al fi-bri-LA-shun), or AF, is the most common type of
arrhythmia
(ah-RITH-me-ah). An arrhythmia is a problem with the rate or rhythm of the
heartbeat. AF can cause blood to pool in the upper chambers of the heart. This
can cause blood clots to form.
Overweight and obesity.
Overweight
and obesity refer to a person's overall body weight and where the extra
weight comes from. Overweight is having extra body weight from muscle, bone,
fat, and/or water. Obesity is having a high amount of extra body fat. These
conditions can lead to atherosclerosis, which increases the risk of blood
clots.
Excessive Blood Clotting That Mainly Affects the
Limbs
Blood clots can form in the veins deep in the limbs.
This condition is called
deep
vein thrombosis (DVT). It mostly affects the deep veins of the legs.
A blood clot in a deep vein can break off and travel
through the bloodstream. When the clot travels to the lungs and blocks blood
flow, the condition is called
pulmonary
embolism (PULL-mun-ary EM-bo-lizm), or PE.
Certain diseases, conditions, or factors may trigger
excessive blood clotting mainly in the deep veins of the limbs. These
include:
- Hospitalization for major surgery or serious
medical illness. This causes nearly half of all cases of DVT and PE. If
youre not able to be active for long periods, blood flow in the veins is
slowed and blood clots may form in the legs.
- Hospitalization for serious trauma and broken
bones. This is the cause of about 12 percent of all blood clots that form in
the deep veins of the legs.
- "Coach class." This term refers to a situation in
which you must stay in one position for a long time, such as in a car or on a
plane. This can slow blood flow and lead to blood clots in the legs.
- Cancer growth and cancer treatment. This accounts
for about 20 percent of blood clots that form in the deep veins of the
legs.
Genetic Mutations
Genetic causes of excessive blood clotting are most
often due to gene mutations (changes to a normal gene).
Common mutations include Factor V Leiden and
Prothrombin G20210A mutations. Fairly rare genetic mutations include proteins C
and S deficiencies and antithrombin III deficiency.
Medicines
Some medicines can disrupt the bodys normal
blood clotting process. Medicines containing the female hormone estrogen are
linked to an increased risk of blood clots. Examples of medicines that may
contain estrogen include birth control pills and hormone replacement therapy.
Heparin is a medicine commonly used to prevent blood
clots. But, in some people, the medicine can cause blood clots and a low
platelet count. This condition is called heparin-induced thrombocytopenia
(HIT).
HIT rarely occurs outside of a hospital, because
heparin usually is given in hospitals. In HIT, the body's immune system attacks
the heparin and a protein on the surface of the platelets. This attack prompts
the platelets to start forming blood clots.
Other Factors That Can Alter the Blood Clotting
Process
A number of other factors also can alter the
clotting process and lead to excessive blood clotting. Common examples
include:
- Smoking. Smoking greatly raises the risk of
unwanted blood clots. It makes it more likely that platelets will stick
together. Smoking also damages the lining of the blood vessels, which can cause
blood clots to form.
- Increased homocysteine levels. Homocysteine is an
amino acid linked to a high risk of vascular disease. Increased levels of this
substance may damage the inner lining of the arteries.
- Pregnancy. Women are six times more likely to
develop blood clots when theyre pregnant. This is because they have more
platelets and clotting factors in their blood during pregnancy. Also, during
pregnancy, the uterus compresses the veins. This slows blood flow, which can
lead to blood clots.
- HIV and HIV treatment. The risk of blood clots is
highest in HIV patients who have infections, are taking certain medicines, have
been hospitalized, or are older than 45.
- Dehydration. This is a condition in which your
body doesnt have enough fluids. This condition causes your blood vessels
to narrow and your blood to thicken. This increases the chance that clots will
form.
- Organ transplants and implanted devices, such as
central venous catheters and dialysis shunts. Surgery or procedures done on
blood vessels may injure the vessel walls. This can cause blood clots to form.
Also, catheters and shunts have a man-made surface that may trigger blood
clotting.
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