Editor's note: This popular story from the Daily Briefing's archives was republished on Jan. 15, 2021.

When Stephan Moll, an expert on coagulation and a professor at the University of North Carolina, was called by NASA to treat an astronaut who had a blood clot, he was presented with a unique problem:  the astronaut was on the International Space Station (ISS) and Moll was on Earth.

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Detecting—and treating—a blood clot in space

According to USA Today, the astronaut was two months into a six-month stint at the ISS. While conducting neck ultrasound examinations as part of a NASA study on how weightlessness effects blood flow, the astronaut detected a blood clot, or deep vein thrombosis (DVT), USA Today reports. NASA has not revealed the name of the astronaut, nor the time frame of the event, to protect the astronaut's privacy, but the astronaut's treatment was detailed in a case study published last week in the New England Journal of Medicine.

While the astronaut did not have any symptoms or family history of blood clots, "the discovery of the potentially perilous condition in such a remote locale called for a quick determination of which action to take, if any," USA Today reports. So NASA reached out to Moll and asked him to consult on the astronaut's treatment, but there was one catch: Much to Moll's disappointment, he would have to do the consultation from Earth, while the astronaut remained in space.

Moll said his immediate concern was that any worsening of the clot could be dangerous. Moll explained that blood clots aren't always dangerous and often dissolve on their own, but he was concerned that the astronaut's clot could expand toward the brain, potentially leading to stroke-like symptoms, or travel toward the heart, resulting in a pulmonary embolism. "On Earth we would feel comfortable just observing the person and not treating with blood thinners, because if things get worse, you can always do some intervention," Moll said. However, he noted, "There are emergency rooms here, but in space you don't have that option."

On the other hand, Moll also was concerned about treating the astronaut with blood thinners, particularly given the astronaut's access to care was limited. He said, "There is some risk when taking blood thinners that if an injury occurs, it could cause internal bleeding that is difficult to stop. In either case, emergency medical attention could be needed."

After considering the chances of those outcomes, Moll and NASA physicians chose to treat the astronaut with blood thinners. But that presented more problems: There was only a limited supply of blood thinners aboard the ISS, and they were in liquid form.

According to USA today, it initially "was difficult and time-consuming for the astronaut to receive the shots of medicine because the liquid clung to the vial in zero gravity." Ultimately, NASA sent a new supply of the blood thinners to the ISS 43 days later, in pill form, USA Today reports.

Meanwhile, the astronaut continued to update doctors on his condition by doing regular ultrasound checkups. According to mobihealthnews, the astronaut "was asymptomatic" six months after he returned to Earth.

A case with unique challenges, but familiar solutions

The astronaut's case presented Moll and his team with a unique set of challenges. For example, there was no history of similar cases, as this was the first-known instance of an American astronaut developing a blood clot while in space, USA Today reports. In addition, there's not much research on how isolated inter-jugular clots will behave if left untreated, nor how often they recur—even in patients on Earth.

However, much of the case was just like treating any other patient, Moll said, noting that he relied heavily on telemedicine to treat the astronaut. "It was almost like a regular clinic visit," he said.

But Moll noted that the case could serve as an example for greater use of telemedicine in the future, as well as an opportunity for further research.

"[I]n my field of hematology and coagulation, telemedicine or electronic consultations (like this) will and should play a big role in the future, so people don't have to travel to the clinic," Moll said.

And while it's still unclear whether the zero-gravity environment or any other factors related to being in space contributed to the development of the astronaut's blood clot, Moll said the NASA study the astronaut was working on found that blood flow was abnormal in half the astronauts studied, although their bodies adjusted to the change. Moll and other physicians in the case study called for more research into the risks of blood clots in zero-gravity conditions.

Maja Zaric, an interventional cardiologist at Lenox Hill Hospital who was not involved with the case, seconded that request. "The study results open the door for much-needed research dedicated to space medicine and subjects exposed to zero-gravity state, and will surely have major implications on future space endeavors," she said (Ortiz, USA Today, 1/8; Lovett, mobihealthnews, 1/7).