Chris Bosh’s NBA career is in jeopardy because of blood clots. Here are five things you should know

Things are getting complicated for 11-time NBA All-Star Chris Bosh, whose career with the championship-winning Miami Heat may be coming to an end because of recurring blood clots. Bosh, who failed his physical on Friday, has been going back and forth with team leadership over whether he can play. As the New York Times reports, Bosh says he can; team doctors and leadership, whether out of concern for Bosh’s health or fear of liability, say no way.

Blood clots — also called venous thromboembolism — have sidelined the 32-year-old at several points during the past two seasons. One clot traveled to Bosh’s lungs and was serious enough that he had to go to the hospital.

So what exactly is a blood clot? Why are they so dangerous?

Here are five things you need to know about an illness that may permanently sideline one of the NBA’s greats.

1. Blood clots are often misdiagnosed, especially in athletes

Blood clots form when we get injured and typically they dissolve on their own. But sometimes they form in veins and don’t dissolve. At one point, Bosh complained of pain in his calf — the most common symptom of a blood clot known as deep vein thrombosis (DVT). But for athletes that work out for hours each day, leg pain could just be dismissed as normal wear and tear.

If a clot travels to the lungs, though, things could get more serious. Dr. Martina Trinkaus, a hematologist in Toronto, said that type of clot, called pulmonary embolism, usually comes with shortness of breath and a rapid heart rate. Untreated, about 25 percent of lung clots are fatal. For instance, she said, “for conditioned athletes who should have a low resting heart rate, a rate over 100 is alarming and should be investigated,” said Dr. Trinkaus.

2. Athletes are at higher risk for blood clots

Three things that set athletes apart from weekend warriors also put them at higher risk for blood clots: a low resting heart rate, getting dehydrated during a game, and hopping a long flight. Dr. Rudolph Virchow, one of the founding fathers of modern medicine, outlined three main origins of blood clots:

• Medical issues that lead to high blood clotting risk factors, like surgery or cancer
• Damage to blood vessels, as in heart disease or the placement of an IV
• Anything that causes blood to move more slowly through the body, like varicose veins, being sedentary, or having a low heart rate

In contact sports, especially the NBA, there’s a lot of jostling and body checking. Vessels get damaged. Clots could form. The jury’s out on whether vigorous sports increase the risk of blood clots. Some clotting factors increase during exercise. Others go down.

3. Treating DVT is not easy and often leads to problems afterward

Bosh told the New York Times that he was working on a plan with his doctors; that plan likely includes blood thinners like rivaroxaban. The problem with many blood thinners is that they aren’t easily reversible. A few hard bumps and Bosh could bleed uncontrollably. Another option is warfarin, but it can interact negatively with food and other medications. One of the biggest challenges of treating blood clots is post-thrombotic syndrome — it’s a painful and sometimes debilitating after-effect of blood clots. About 1 in 3 people who get clots get the syndrome.

4. It may be harder to get back on the court with clots than a concussion

Dr. Bon Ku, an emergency physician at Thomas Jefferson University Medical Centre in Philadelphia, said players like Bosh have a lot to think about if they get a diagnosis of DVT.

“It has more to do with whether or not they are on anticoagulants. Personally, if the individual is in a contact sport, I would not recommend they continue to play while on blood thinners. The risk is too high, especially for a traumatic head bleed,” Ku says.

The American College of Chest Physicians updated its guidelines earlier this year, saying that if you have more than one clot, you need to be on long-term anticoagulation therapy. This could explain why elite athletes in contact sports retire after a second clot episode.

5. For weekend warriors, blood clots are preventable

Athletes with blood clotting disorders may not want to talk about them, said Trinkhaus, because they may not be able to play.

And while explosive exercise like professional basketball may be putting Bosh at risk, for the rest of us, the National Heart, Lung and Blood Institute says that general exercise, water, walking around on airplanes, and being vigilant about symptoms are the best ways to avoid blood clots. Compression socks may help, too.