Prevent This Hidden Killer

Blood clots are claiming the lives and careers of more and more high-profile athletes. Here’s why. By Mary Cushman, M.D., M.Sc.

We keep hearing news stories about elite athletes developing abnormal blood clots.

In 2015, retired Portland Trail Blazers’ legend Jerome Kersey died at age 52 of a pulmonary embolism (PE) about a week after minor leg surgery. Miami Heat star power forward Chris Bosh had a PE in February 2015 and missed the rest of the season while undergoing treatment. He was sidelined again in 2016 reportedly after a deep vein thrombosis (DVT) in occurred in his legs and is missing the NBA Playoffs.

Star forward Steven Tampkos from the Tampa Bay Lightning had a DVT in the arm veins and underwent surgery in April 2016 to remove a rib that was reducing blood flow.

Perhaps the most well-known athlete to experience a blood clot is the tennis icon Serena Williams, who had life-threatening pulmonary embolism (PE) in 2011 after a foot injury and cross-country air travel.

Why would these super-healthy people get blood clots?

Here’s why: Abnormal blood clots can occur in the leg veins. This is called deep vein thrombosis, or DVT. It causes leg pain, swelling and sometimes color change like red streaks. DVT can also be present without any symptoms. Sometimes when there is a DVT, pieces of the blood clot break free and travel to the lungs. This can be deadly and is called pulmonary embolism or PE. But when caught earlier on, these types of blood clots can be treated with blood-thinning medications, also called anticoagulants.

This problem is serious. These clots occur in up to 900,000 people each year in the United States and about 100,000 people die from them. This is more people than die from breast cancer, AIDS and car accidents combined. About one or two middle-aged person in every 1,000 gets blood clots every year. The rate is lower in younger people (about one to two in every 10,000.)

So, just by chance athletes could get clots. But there are special risk factors that athletes should look for.

Obesity is a risk factor for these abnormal clots. Most pro athletes aren’t obese, but research suggests that larger people, like those who are taller or have bigger legs, are at risk. This is because the ability of blood to flow up the legs is more problematic for bigger people. So for some athletes, especially basketball players who tend to be very tall, risk might be higher. It’s interesting that we don’t hear many reports of NFL players with clots, as they are more likely to have obesity. It may be that it is just less often reported; no research is available.

Athletes who use their arms heavily, like paddlers, tennis players, baseball pitchers and basketball players, are at risk of clots involving the arm veins. These clots can occur when a structure at the base of the neck (next to the shoulder) called the thoracic outlet is narrowed. The vein, artery and nerve supplying the arm has to pass through this outlet, which is lined by muscles and bony structures.

For athletes, especially those using their arms, the muscles can get large and contribute to the narrowing of the outlet. In this situation, repetitive injury to the vein going through that narrowed outlet sets the stage for a clot forming in the vein. These clots can cause swelling and pain of the arm, and sometimes numbness. Like leg clots, they can travel to the lungs causing pulmonary embolism. Treatment is with anticoagulant medications and often surgery is used to open up the outlet so that clots might not form again.

Injuries are a major source of risk for clots, especially leg injuries that result in leg immobility afterwards. The worst example of this is a leg fracture with casting. However, minor injuries also can increase the risk somewhat; this is likely a factor for hockey players as they often get hit by the puck.

Surgery greatly increases the risk of blood clots for a period of several weeks. The risk is greater for orthopedic than general surgery, so it is a factor for athletes. In 2013, NBA Star Anderson Varejao’s great season with the Cavaliers was cut short when he developed back and chest pain from a PE shortly after surgery on his quadriceps. His case proved that this condition doesn’t have to end a sports career; Varejao apparently had a finite treatment with anticoagulation and is currently playing for Golden State in the NBA playoffs.

Like anyone else, genetics plays a role for athletes. Kimmo Timonen, four-time NHL All Star with the Philadelphia Flyers developed a leg DVT and PE in 2014. He had had less serious superficial clots (in veins just under the skin) previously, which we know is a risk factor for DVT and PE. He was found to have protein C deficiency, a genetic condition that contributes to blood clot risk by lowering the body’s ability to stop formation of clots.

Travel: We know that long travel slightly increases the risk of clots, and pro athletes travel a lot.

Birth control pills increase the risk of clots in women. This risk is highest in the first year of use and among older women who are on the pill. The risk continues until the pills are stopped.

There are no medical guidelines yet on the best treatment for athletes so we customize treatment recommendations the same way we do for non-athletes. If the blood clot was limited to the arm veins or triggered by surgery, trauma or immobilization, usually 3 months of anticoagulation treatment is adequate.

Mary Cushman, M.D., M.Sc., a professor of medicine and director of the Thrombosis and Hemostasis Program at the University of Vermont.