What Causes a Thrombus?

A thrombus is a blood clot that forms inside a blood vessel; they are dangerous because they may break free to become an floating embolism that can block vital arteries or veins.

A thrombus is a blood clot in a blood vessel. A thrombus may form in a vein (venous thrombosis) or artery (arterial thrombosis). 

If a thrombus breaks free and enters the bloodstream, it is called an embolus.

Symptoms of a thrombus (blood clot) may include:

• Swelling, pain, warmth, tenderness to the touch, and redness in the affected area
• Frequently occurs in the calf or inner thigh (deep vein thrombosis, or DVT)
• Swelling in the leg or arm
• Cramp-like feeling
• Chest pain
• Numbness or weakness on one side of the body
• Abrupt change in mental status

If a thrombus breaks off and travels to the lung, this is called a pulmonary embolism (PE), which is a medical emergency and can be fatal. Symptoms of pulmonary embolism include:

• Shortness of breath with no known cause
• Unexplained cough
• Chest pain
• Increased heart rate
• Fatigue
• Passing out (syncope) 

Causes of a thrombus in a vein (venous thrombosis) include:

• Injury to the leg veins
• Illness that affects the veins
• Immobility
• Broken bone
• Certain medications
• Obesity
• Inherited (genetic) disorders
• Autoimmune disorders that increase the risk of blood clots
• Medicines that increase the risk of blood clots (such as certain birth control hormones)

Causes of a thrombus in an artery (arterial thrombosis) include:

• Injury to the artery
• Infections such as sepsis or viral infections
• Hardening of the arteries (atherosclerosis)
  • If this occurs in the coronary arteries it can lead to a heart attack
  • If this occurs in a blood vessel in the brain, it can lead to a stroke

Risk factors for both venous and arterial thrombosis include:

• Family history or personal history of blood clots such as deep vein thrombosis (DVT)
• Immobility, such as from long flights or after surgery
• Older age
• Smoking
• Being overweight or obese

Additional risk factors for venous thrombosis include:

• Use of birth control pills or hormone therapy
• Pregnancy
• Injury to a vein, which may occur from surgery, a broken bone, or other trauma
• Inherited blood clotting disorders
• A central venous catheter
• Certain conditions, such as cancer, heart disease, lung disease, or Crohn's disease

Additional risk factors for arterial thrombosis include:

• Diabetes
• High blood pressure (hypertension)
• High cholesterol
• Sedentary lifestyle 
• Poor diet

Thrombus (blood clot) is diagnosed starting with a medical history and a physical exam. Tests for thrombus may include:

• Ultrasound
• Blood tests to see how well blood clots
  • D-dimer test
• Venography
• Magnetic resonance imaging (MRI)
• Magnetic resonance angiography (MRA) 
• Computerized tomography (CT) scan

Treatment for a thrombus (blood clot) may include:

• Use of compression stockings
• Blood-thinners (anticoagulants)
  • Direct oral anticoagulants (DOACs):
    • apixaban (Eliquis),
    • dabigatran (Pradaxa),
    • edoxaban (Savaysa), and
    • rivaroxaban (Xarelto)
  • Vitamin K antagonist:
    • warfarin (Coumadin) 
  • Low-molecular-weight (LMW) heparin:
    • dalteparin (Fragmin),
    • enoxaparin (Lovenox), and
    • tinzaparin (Innohep)
  • Fondaparinux (Arixtra)
  • Unfractionated heparin
• Thrombolytic medicines to dissolve blood clots, like 
  • anistreplase (Eminase),
  • reteplase (Tetavase),
  • streptokinase (Streptase),
  • alteplase (Activase),
  • tenecteplase (TNKase),
  • urokinase (Abbokinase), and
  • rokinase (Kinlytic)
• Catheter-directed thrombolysis to deliver medication directly to a clot so it dissolves
• Thrombectomy surgery to remove a blood clot
• Use of a stent (wire mesh tube) to keep a blood vessel open 
• Use of vena cava filters in which filters are placed in the vena cava (the body’s largest vein) to trap blood clots so they don’t migrate to the lungs and cause pulmonary embolism 

Complications of a thrombus (blood clot) include:

• Heart attack
• Stroke
• Breathing problems
• Bleeding risks from taking anticoagulants

You may be able to reduce the risk of developing a thrombus (blood clot):

• Get regular exercise and stay active
• Lose weight if you’re overweight
• Don’t smoke
• Stay hydrated
• During long flights, move your legs or wear compression stockings to improve blood flow
• Return to activity as soon as possible after surgery
• Manage diabetes, high blood pressure, and high cholesterol