Scientists have described how, for the first time, a space station astronaut’s blood clot was successfully treated by doctors more than 200 miles away on Earth.

The incident is revealed in a paper entitled “Venous Thrombosis during Spaceflight,” published in the New England Journal of Medicine. The research could have major implications for long-term space missions, particularly as the U.S. plans a return to the Moon and future missions to Mars.

The paper’s lead author is Dr. Serena Auñón-Chancellor, clinical associate professor of Medicine at Louisiana State University Health New Orleans School of Medicine's branch campus in Baton Rouge and a member of NASA’s astronaut corps. Auñón-Chancellor is board certified in both internal and aerospace medicine.

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In the paper, researchers describe the “case of stagnant blood flow resulting in a clot in the internal jugular vein of an astronaut,” on the ISS, according to a statement released by Louisiana State University Health Sciences Center. The identity of the astronaut has not been revealed.

The International Space Station - file photo. (NASA)

The astronaut’s blood clot was discovered during a vascular study that involved 11 astronauts. “The study measured the structure and function of the internal jugular vein in long-duration spaceflight where astronauts are exposed to sustained headward blood and tissue fluid shifts,” scientists explain, in the statement.

During the mission, ultrasound exams of the astronauts’ internal jugular veins were performed at scheduled times in different positions. However, about two months into the mission, an ultrasound exam revealed a suspected blood clot in one astronaut. A follow-up ultrasound, guided by two radiologists on Earth, confirmed the blood clot.

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Researchers note that NASA had never encountered this situation in space before, so scientists had to weigh the risks of the clot traveling and blocking a vessel in the astronaut’s body versus using anticoagulation therapy in microgravity. “The space station pharmacy had 20 vials containing 300 mg of injectable enoxaparin (a heparin-like blood thinner), but no anticoagulation-reversal drug,” the scientists explained. “The injections posed their own challenges - syringes are a limited commodity, and drawing liquids from vials is a significant challenge because of surface-tension effects.”

TV station WRAL reports that Dr. Stephan Moll, an expert in thrombosis at the University of North Carolina School of Medicine, was brought in by NASA to help treat the astronaut. Moll, along with Dr. James Pattarini of NASA’s Johnson Space Center and Dr. Ashot Sargsyan of KBR in Houston, was a co-author of the paper published in the New England Journal of Medicine.

Ultimately, the astronaut was treated with enoxaparin, with the dosage reduced after 33 days. This meant that the supply of the blood thinner lasted until apixaban, an oral anticoagulant, could arrive on a supply spacecraft to the orbiting lab. Scientists on Earth also sent anti-coagulation reversing agents on the supply ship.

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“Although the size of the clot progressively shrank and blood flow through the affected internal jugular segment could be induced at day 47, spontaneous blood flow was still absent after 90 days of anticoagulation treatment,” scientists added, in the statement. “The astronaut took apixaban until four days before the return to Earth.”

After the astronaut’s return to Earth, an ultrasound revealed that the clot had flattened and no further anticoagulation was needed. The clot was present for 24 hours after landing and was gone 10 days later. The astronaut, who had no family history of blood clots, was asymptomatic six months after their return from space.

Scientists say that further research is needed on changes in blood organization and flow in space.

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"These new findings demonstrate that the human body still surprises us in space," Auñón-Chancellor said in the statement. "We still haven't learned everything about Aerospace Medicine or Space Physiology."

NASA told Fox News that the research findings are significant. "The clinical case study just published in the New England Journal of Medicine about the deep vein thrombosis treated during a space mission and the NASA-supported important research previously published that highlighted how blood flows from the brain in microgravity are important medical findings," it said, in an emailed statement. "NASA is committed to monitoring blood flow dynamics to protect astronauts’ health and performance in current International Space Station missions and future missions to the Moon and Mars."

"NASA will continue to monitor future astronauts for blood flow stasis with routine on-orbit screening ultrasounds and has ensured the International Space Station is equipped with appropriate treatments in the medical kit available to crew members," the space agency added.

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Auñón-Chancellor and her crewmates Alexander Gerst of the European Space Agency and Russian Cosmonaut Sergey Prokopyev returned to Earth on Dec. 20, 2018, following a 197-day stint on the International Space Station. The mission was Auñón-Chancellor's first trip to the ISS.

The coming years are set to be particularly momentous for the U.S. space program. NASA’s Artemis program, fox example, aims to land American astronauts on the moon by 2024 and establish a sustainable human presence on Earth’s natural satellite.

NASA’s long-term goal is to send a crewed mission to Mars in the 2030s.

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"Studying the health of astronauts before, during, and after their missions is important to protecting the health of our crew members who are leading NASA’s human space exploration program that will land the first woman and next man on the Moon through the Artemis program," said NASA, in the statement emailed to Fox News.

While NASA wants to send astronauts to Mars in the 2030s former astronaut Buzz Aldrin thinks that a slightly later target date of 2040 is more realistic. In an interview in 2016, the Gemini 12 and Apollo 11 astronaut told Fox News that by 2040, astronauts could have visited Mars’ moon Phobos, which could serve as a sort of stepping stone to the Red Planet.

Follow James Rogers on Twitter @jamesjrogers