What Causes Blood Clots in Legs (and Increases Your Risk)?

Patty Weasler, RN, BSN
·6 min read
7

Medically reviewed by Renee Nilan, MD

A blood clot in the leg, also known as deep vein thrombosis (DVT), is a serious medical condition that has several risk factors and causes.

Blood clots can occur in anyone, however, people are at increased risk after surgery and while pregnant.

This article will discuss the causes and risk factors for blood clots in the legs. It will also cover ways to prevent clots and emergency symptoms.

6 Causes of Blood Clots in Legs

A blood clot forms in the legs when a blood vessel is damaged or when blood moves slowly through the vessel. Below are the causes of blood clots in the legs.

Blood Vessel Injury

When a blood vessel is cut or injured, it bleeds. The body's natural response is to form a clot to stop the bleeding.

Clotting is a complex process in which damaged cells send chemical signals that start the clotting process. Platelets will gather to plug the hole in the blood vessel. Then, fibrin strands will cover the wound to strengthen the platelet plug and seal the wound.

Once the blood clot forms, the body's immune system works to heal the wound. This is when the elements in the blood start to break down the clot.

Slow Blood Flow

Another way that blood clots form in the leg is when blood moves too slowly. This causes platelets to stick together and form a clot. Since this is happening inside the blood vessel, it is dangerous.

A blood clot inside the blood vessels of the legs, known as deep vein thrombosis (DVT), can block blood flow. A DVT can break free and get trapped in the lungs, causing a pulmonary embolism (PE). Blood clots can also get trapped in other organs like the heart and brain.

Blood slowly moves through vessels for several reasons, which include:

  • Sitting for long periods

  • Bed rest, especially after surgery

  • Long-distance travel

  • Sedentary lifestyle

Surgery

Surgery is a common cause of blood clots in the legs. This is due to several factors. One is that when someone is having surgery, they are not moving for an extended period of time. This slows down blood flow.

Another reason surgery causes blood clots is injury to the blood vessels. Surgery naturally involves damage to vessel walls, which releases clotting factors into the bloodstream.

Surgery also causes blood to thicken, which increases the risk of clots. During surgery, tissue, fat, or other debris can be released into the bloodstream. When the body identifies this, it clots around the foreign matter.

Pregnancy and Delivery

According to the Centers for Disease Control and Prevention (CDC), pregnant people are 5 times more likely to develop a blood clot than those who are not.

The risk of blood clots increases during the first three months after delivery. The body naturally increases a person's ability to clot during pregnancy to reduce blood loss during labor and delivery.

Pressure from the baby on the pelvic blood vessels can decrease blood flow, increasing the chances of a blood clot.

Another reason pregnancy and delivery increase the chances of a blood clot is that the mother may have decreased mobility, which can limit blood flow to the legs.

Cancer

About 1 in 5 blood clots are due to cancer. It is believed that tissue damage from cancer can activate blood clotting.

Pancreatic and lung cancers are two types of cancer in which blood clots are common. Metastatic cancer is also known to be a blood clot risk factor.

Some cancer drugs have been connected with blood clot formation. These medications are:

  • Platinum (cisplatin)

  • L-asparaginase

  • Thalidomide

  • Tamoxifen

  • Lenalidomide

  • Vascular endothelial growth factor inhibitors (bevacizumab)

Hormonal Birth Control

Birth control pills slightly increase the likelihood of forming a clot. The risk of developing a clot while on birth control is higher in women over 40 years old, those with a family history of vascular disease, those who smoke, and those who are overweight.

Birth control pills that contain desogestrel, dienogest, gestodene, and drospirenone seem to increase the risk of blood clots more than other types of birth control pills.



How Long Does a Blood Clot Last?

A blood clot will naturally dissolve on its own in a few weeks to months after its formation. If a thrombolytic (clot buster) medication is given to someone with a clot it will dissolve much faster. There is a significant risk of bleeding associated with thrombolytic mediations and they are only used in specific circumstances.



What Increases the Risk of Leg Blood Clots?

Just about anyone can develop a leg blood clot. Risk increases with the following factors:

  • Smoking: This raises the risk of unwanted blood clots and makes it more likely that platelets will stick together.

  • Age: Risk doubles every 10 years after the age of 40.

  • Gender: Before menopause, women are more likely to get a blood clot.

  • Family history: Experts have found inherited genetic variations that increase the risk of blood clots.

  • Obesity: Causes inflammation and damages blood vessel lining.

  • Diabetes: Increases plaque buildup in arteries, which leads to blood clots.

  • Certain medical conditions: Heart disease, kidney disease, Crohn's disease, and ulcerative colitis.



Emergency Blood Clot Symptoms

A blood clot in the leg can become a medical emergency. The blood clot can dislodge from the vein and travel to the lungs, blocking blood flow to the lungs. This is called a pulmonary embolism (PE). Symptoms that would indicate an emergency include:

Early warning signs of a leg blood clot are:

  • Leg swelling

  • Painful to the touch

  • Skin feels warm

  • Skin is red or discolored



Minimizing Leg Blood Clot Risk After Surgery or Delivery

Preventive measures can reduce the chances of a blood clot after surgery or delivery.

  • Movement: Move around as soon as a healthcare provider permits after surgery or delivery.

  • Physical therapy: A physical therapist will provide and teach you movements to maintain range of motion, strengthen the legs, and improve leg circulation.

  • Compression stockings: You can wear elastic stockings that are tighter at the ankle and slightly loosen as they get higher on the leg

  • Compression devices: These are devices used in hospitals that are wrapped around the legs and inflated with air. They apply pressure to the calf and improve blood flow.

  • Anticoagulants: People with a high risk of clotting after surgery may be prescribed an anticoagulant medication (a blood thinner) to prevent a blood clot.

More Suggestions to Prevent Blood Clots in Legs

Blood clots can occur in anyone. Prevention can include the following:

  • After sitting for a long time, stand up and walk around every one or two hours.

  • Extend and flex your knees and ankles to pump your legs.

  • Avoid crossing your legs when sitting.

  • Avoid wearing tight clothing.

  • Change positions when sitting.

Summary

Blood clots in the legs can block blood flow through the leg or detach from the vein and travel to the lungs. This is called a pulmonary embolism and is a medical emergency. Incidence is high in people who are having surgery, are pregnant, or have delivered a baby. Using preventive measures like wearing compression stockings can reduce the risk of a blood clot.

Always talk to a healthcare provider to determine your individual risk and measures you can take to stay safe.

Read the original article on Verywell Health.