What you need to know about blood clots Jalen Hurts

A "superficial" blood clot does not mean it is not serious.

For an NFL quarterback, a sore calf might seem like an unsurprising consequence of hitting a dog. In Jalen Hurts' case, the ultrasound revealed something else: a superficial blood clot.

The Philadelphia Eagles quarterback was hit in the leg during an Oct. 4 game and sought treatment four days later, according to a team statement. An ultrasound in London showed a clot, but doctors cleared him to play in the team's game the next day.

Then, a follow-up ultrasound Wednesday night showed "movement in a small blood clot." Hurts will miss Sunday's game against the Carolina Panthers while the team determines his treatment, the Eagles announced Thursday.

What makes a clot superficial—and when does it become dangerous? We asked the doctors for an explanation.

What is the difference between a superficial blood clot and a deep vein thrombosis?

To understand blood clots, visualize the road map. Your deep veins run through the muscles of your arms and legs and carry most of the blood from your limbs to your heart. Superficial veins are located closer to the surface, just under the skin and in the underlying tissue. Connecting veins bridge the two systems.

"You have a completely interconnected network of veins," says Dr. William Schutz, a vascular surgeon at Texas Vascular Associates in Dallas and vice president of the Society for Vascular Surgery (who was not involved in Hearts' care). Think of it as "a highly developed road and highway system" with multiple routes to get where you need to go.

When a clot blocks one pathway, blood can be diverted through other veins.

A superficial clot forms in one of the veins near the skin. The area may become red, warm, and tender. "It's usually very uncomfortable," Schutz says. Some develop in varicose veins. Others form where a needle or needle has irritated the vein.

Sometimes you can feel the damaged vein under your fingers. "It's like a pencil under the skin or a nodule," says Dr. Stephen Mull, a hematologist and professor of medicine at the University of North Carolina who runs an athlete and blood clot clinic (who was not involved in Hartz's care).

Deep vein thrombosis involves a clot farther inside the body. Symptoms can be more widespread — the entire leg or ankle may become swollen and painful, says Moll. You cannot feel the deep vein itself.

Many superficial clots stay in place and heal without blood thinners. But sometimes, the clot grows into one of the deeper veins. A piece can then break off and travel to the lungs, causing a potentially life-threatening complication called a pulmonary embolism.

Schutz says that doctors use ultrasound to evaluate for clots and check for deep vein involvement. They are particularly concerned about superficial clots longer than 5 cm or within 3 cm of the junction of the superficial vein with the deep vein.

The Eagles did not specify those details. And "movement" is not precise enough to specify what happened. "It's not a term we use in clinical practice." It can describe a growing or expanding clot; By itself, it does not indicate that a fragment has broken off or reached the lungs.

How do these clots occur and how are they treated?

Being in good shape does not protect a person from blood clots. Injury can damage the vein, while prolonged inactivity slows blood flow. Surgery, certain inherited clotting disorders, cancer and pregnancy can also increase the risk, says Dr. Alina Mitina, an emergency physician at Hackensack University Medical Center in New Jersey (who was not involved in Hearts' care).

Veins close to the skin have less cushioning when hitting someone. "Deeper veins are protected, although severe trauma can damage them as well," Schutz says.

A clot can form within hours of an injury or over several days, he adds. If your foot already hurts from kicking, you may not be aware of another reason why it hurts.

Traveling can pose another risk: Sitting on a long flight or car ride means the legs don't move enough, reducing blood flow.

Some superficial clots can be controlled with warm compresses, anti-inflammatory medications, elevation, and monitoring. Others need blood thinners to help prevent the clot from growing -- even if it hasn't reached a deep vein.

If blood thinners are needed, the treatment is usually temporary, often lasting a few weeks, says Moll.

This doesn't necessarily mean just recuperating on the couch. "We love them. Be active because we want to keep the blood flowing," says Schütze.

Getting up for a walk is, of course, different from tackling. Schutze worries that athletes will take another hit where they have a blood clot. Blood thinners add another concern: An injury that causes bleeding can be much more dangerous when the blood doesn't clot easily.

"In football, you have significant contact all the time," says Moll, which increases the risk of severe bleeding, including to the head or muscles.

Athletes are used to pain. "They often minimize the clinical signs, quite understandably, because they don't want to be delisted," says Moll.

Notice when the discomfort feels different, persists, or worsens. Pain, swelling, discoloration, and heat can be signs of a clot. Mitina says patients sometimes describe leg cramps. Redness around a superficial clot can resemble an infection.

If you think you might have a superficial clot, "don't ignore it," says Shutze. Have a doctor check it out rather than just assuming it's a bruise or muscle strain.

Unexplained shortness of breath, chest pain, coughing up blood, or fainting require emergency care because they can be signs of a pulmonary embolism. Mole also cites unexplained coughing and rapid heart rate as possible warning signs.

And getting checked once doesn't mean you have to dismiss symptoms that persist or worsen. "Always go to the emergency room if something seems strange or if symptoms don't improve," Mitina says. "You know your body better."