Blood Clot Symptoms: What to Watch Out for, and When to See a Doctor

Heart attack, stroke, pulmonary embolism—all three medical emergencies happen in different parts of the body, and yet they have something in common: They can all be caused by a blood clot.

According to the National Blood Clot Alliance (NBCA), approximately one person dies every six minutes as a result of a blood clot. They're so dangerous because they can impede or block blood flow to vital organs in the body, Amita Avadhani, PhD, associate professor, Advance Practice Division, School of Nursing at Rutgers, The State University of New Jersey, tells Health. "Our vital organs such as brain, lungs, and heart need oxygen to function. Without oxygen, the brain cells start dying after four minutes, causing permanent damage to the organs and their functionality as the time progresses."

Not all blood clots are created equal, though. Blood clots "can range from mildly symptomatic and recoverable to fatal," Elad I. Levy, MD, professor and chair of neurosurgery at the University at Buffalo, tells Health.

While your overall risk of having a blood clot is fairly low, they can and do happen. Here's what you need to know about blood clots and their symptoms.

What exactly is a blood clot?

Your blood is typically in a liquid state, but a blood clot is a gel-like clump of blood, the Mayo Clinic explains. Blood clots can be helpful in certain situations, like when you have an injury or a cut, to help plug the injured blood vessel and stop the bleeding.

But blood clots can form inside your body without a good reason, and block blood vessels—this is called thrombosis. Those can travel to critical areas of your body, like your lungs, brain, or heart, causing serious and sometimes fatal complications like a pulmonary embolism (when a blood clot travels to your lungs), a stroke (when one reaches the brain), or a heart attack (a blood clot in the heart).

What are the types of blood clots?

In order for blood to reach all parts of your body—from the top of your head to the tip of your toes—you have a circulatory system which is made up of blood vessels called veins and arteries. (Arteries carry oxygen-rich blood from the heart to other parts of the body; veins carry oxygen-poor blood back to the heart to get reoxygenated.)

Because there are two types of vessels that carry blood throughout your body, there are also two types of blood clots: arterial clots, which occur in the arteries, and venous clots, which form in the veins.

Blood clots can also be categorized based on their movement—or whether or not they're mobile. According to MedlinePlus, a blood clot that forms inside a vein or artery is called a thrombus (these can also form in your heart). But a blood clot that breaks free and moves from one part of the body is known as an embolus (or the plural form, emboli).

Arterial clot

This type of blood clot—known as an arterial embolism, when the clot or thrombus comes from elsewhere in the body—usually happens in the legs and feet, and interrupts blood flow to other parts of the body, according to the US National Library of Medicine's MedlinePlus resource. Symptoms come on quickly or slowly, depending on the size of the clot and how much it blocks the flow of blood. You may not have any symptoms at all, per MedlinePlus.

Symptoms of an arterial clot or embolism in the legs or arms include:

• A cold arm or leg
• Decreased or no pulse in an arm or leg
• Lack of movement in the arm or leg
• Pain in the affected area
• Numbness and tingle in the arm or leg
• Pale color of the arm or leg
• Weakness of an arm or leg

The longer an arterial clot blocks blood flow, other symptoms can emerge:

• Blisters on the skin near the affected artery
• Skin shedding
• Skin erosion (ulcers)
• Tissue death, or necrosis.

If an arterial clot occurs in an organ, symptoms depend on the affected organ. An arterial clot that occurs in the brain can lead to a stroke, and one that forms in the heart can lead to a heart attack. But arterial clots can also show up in the kidneys, intestines, and even eyes—though those are rare. In general, symptoms of arterial clots in organs look like:

• Pain in that part of the body
• Temporarily decreased organ function

Venous clot

A venous clot forms in a vein and can build up over time. The most serious form of a venous clot is deep vein thrombosis (DVT), a condition that happens when a blood clot forms in a deep vein—as opposed to more superficial veins that are closer to the body's surface—the CDC says. Those clots usually develop in the lower leg, thigh, or pelvis, but they can also occur in the arm.

The most serious complication of DVT happens when a part of the clot breaks off and travels through the bloodstream to the lungs, the CDC explains. There, it can cause a blockage called pulmonary embolism (PE), stop blood from flowing to the lungs, and lead to death. DVTs, however, do not lead to heart attacks or stroke, per the CDC.

Symptoms of DVT can include:

• Swelling
• Pain
• Tenderness
• Redness of the skin

Symptoms of a PE can include:

• Difficulty breathing
• Faster than normal or irregular heart beat
• Chest pain or discomfort, which usually worsens with a deep breath or coughing
• Coughing up blood
• Very low blood pressure, lightheadedness, or fainting

Cerebral venous sinus thrombosis (CVST) is also a venous clot, forming in the brain's venous sinuses, Johns Hopkins Medicine explains. This type of clot—which has recently been linked to a temporary pause on the Johnson & Johnson COVID-19 vaccine after six women developed one—keeps blood from draining out of the brain, which can cause blood to leak into the brain's tissues.

Symptoms of a CVST can include:

• Headache
• Blurred vision
• Fainting or loss of consciousness
• Loss of control over movement in part of the body
• Seizures
• Coma

When should you see a doctor about a blood clot?

If you have any symptoms of a blood clot, seek medical attention ASAP. "You need to be seen," Anita Gorwara, MD, family medicine physician and medical director of urgent care at Providence Saint John's Health Center in Santa Monica, Calif., tells Health. "Don't waste time calling your doctor and waiting for them to get back to you. Go to an urgent care center, your primary care physician's office, or the emergency room, right away."

Timing matters with blood clots. "Cells start dying after four minutes of lack of circulation," says Avadhani. "This is why when someone has a stroke, the chance of damage to the brain can be minimized or eliminated if the clot is identified and treated promptly."

Dr. Levy stresses the importance of not brushing off your symptoms. "If you're unsure, don't assume it's nothing," he says. "Go get checked out."