A blood clot is a gel-like group of blood cells that can form in veins, arteries and capillaries. If something damages your delicate blood vessels, they are your first line of defense to stop bleeding too much after an injury or surgery.

However, blood clots can be dangerous under certain circumstances. Knowing the warning signs can save your life. A quick response can help prevent complications, scarring and long-term damage.

Vascular surgeon Mrinalini Patil, MD, explains the most common vein blockages, their symptoms, risks and when to take action.

The most common types of venous blood clots

• Deep vein thrombosis (DVT): A blood clot that forms in a deep vein, most often in the legs and less commonly in the arm, under the clavicle or in the belly.

• Pulmonary embolism (PE): A blood clot that breaks off and travels to the lungs, blocking blood flow and oxygen. A PE is life-threatening and requires immediate medical care.

Pay attention to the warning signs

Symptoms may vary from one person to another, ranging from mild to severe. Pay close attention to sudden symptoms that linger and don’t improve. Symptoms tend to be constant, not pain or swelling that comes and goes.

DVT symptoms typically occur in one limb (arm or leg) and may include:

• Sudden, constant pain.
• Heaviness.
• Swelling.
• Redness, with or without warmth.
• Numbness, weakness or extreme tightness (more severe).
• Blue or white discoloration (more severe).

PE symptoms include: 

• Chest pain that is constant or occurs while taking deep breaths.
• Shortness of breath that is new, unexplained and lingers.
• Heart palpitations with low blood pressure.
• Coughing up more than a tablespoon of blood.

Risk factors for developing blood clots

• Sitting for long periods, such as with long flights, long drives, a sedentary job or after surgery.
• Inherited genetic conditions that include clotting disorders or coagulopathy.
• Medical conditions like heart disease may increase your risk. 

“When you sit for long periods, it’s important to take breaks to walk around,” says Dr. Patil. “When you walk, those muscles contract and keep the blood moving up the veins. When blood doesn’t move, that’s when problems develop.” 

Having an underlying condition does not necessarily mean you are more prone to clots unless you also have a significant risk factor.

When to seek medical care

When and where to call depends on your symptoms and the type of clot you may have. Seeing your doctor (or going to the emergency room if symptoms are severe) is essential because you likely won’t know which type you're experiencing.

“A blood clot can go away on its own, but it depends on which vein it is in,” says Dr. Patil. “If they’re in the deeper, bigger veins in the leg, without treatment, they’re less likely to go away and can move or change. This can cause bigger issues if not treated in a timely fashion, and the consequence of missing a large clot can be life-threatening if it moves.”

Go to the emergency room immediately if you have:

• PE symptoms, especially chest pain and shortness of breath.
• Sudden leg symptoms like severe discoloration or numbness.
• Severe weakness in the leg or no feeling in your foot where you can’t move. 

Call your primary care physician if:

• Your symptoms occur in the leg or arm.
• If your symptoms are ongoing (more than a day or two) and get noticeably worse.

An ultrasound will be used for a suspected DVT clot, and a CT scan for suspected PE. Blood clots cannot be seen on an X-ray.

“Treatment within several days is essential to prevent complications,” adds Dr. Patil. “If you can’t get in to see your primary care physician under two weeks, go to urgent care if you can get an ultrasound there. If you’re experiencing severe symptoms or those as with PE, go to the emergency room.”

How to help prevent blood clots

Movement is key to prevention:

• Walk every one to two hours during travel or prolonged sitting.
• Wear compression socks on long flights, during working hours if you sit all day or have a sedentary lifestyle.

Blood clot treatment and outcomes

When blood clots are caught early (within one to two weeks), treatments are highly effective, and you’re less likely to have long-term complications. 

First-line treatment typically includes blood thinners, which helps dissolve and prevent the clot from breaking up or getting worse. In severe cases, minimally invasive surgical procedures may be used to remove clots. If symptoms do not improve with blood thinners, minimally invasive surgery may be an option.