NASA seeks better evidence on blood clots in space
NASA is seeking research on monitoring, preventing and treating blood clots in space. The current solicitation is due November 20, 2026. It is a research request, not a proven preventive treatment.
NASA is seeking research on how to monitor, prevent and treat blood clots during spaceflight. Its September 25 announcement asks researchers for plans and budget quotations, while an active Johnson Space Center solicitation lists November 20, 2026, at 1 p.m. Central Standard Time as the deadline for offers. The announcement concerns work still to be proposed and evaluated. It does not report a newly proven treatment, a completed prevention trial or the award of a research contract. The procurement notice identifies the opportunity as Venous Thrombosis, reference 80JSC026Q0014. It is a request for quotations under a combined synopsis and solicitation, rather than a report of clinical findings. The stated evaluation factors are technical acceptability, past performance and price, with the first two together carrying more importance than price. An amendment corrects a spelling error in the documents. These details describe how NASA intends to evaluate offers; they are not evidence that a particular medical approach already works in orbit. NASA says the requested research may be retrospective or prospective and may examine existing, enhanced or novel approaches. Applicants are asked to explain their methods and the rationale for validation. Monitoring, prevention and treatment are separate parts of the request. The agency also notes that a clot may be present without symptoms and can be detected using ultrasound. That distinction matters to the subject of the call: identifying an abnormality is a different question from demonstrating that a proposed intervention prevents harm. The concern has a documented history. A 2019 study in JAMA Network Open followed 11 International Space Station crew members. Around flight day 50, six showed stagnant or reversed flow in the left internal jugular vein. One astronaut had a confirmed obstructive clot; a possible second clot was identified retrospectively. Those observations came from a small research cohort, not from a survey establishing the frequency of blood clots in all astronauts. The authors called for more comprehensive examination of venous circulation during spaceflight. That study also tested lower-body negative pressure, which draws blood toward the lower body. Flow improved during 10 of 17 sessions. The researchers described it as a potentially useful countermeasure, while noting unanswered questions about exposure duration, frequency and whether benefits persist. Improved flow in those sessions was not a demonstration that the intervention prevented thrombosis. The study examined the left jugular vein, leaving the right side outside that assessment. A subsequent occupational surveillance study, published in Vascular Medicine in 2022, examined both jugular veins in 11 NASA astronauts using terrestrial and in-flight ultrasound. No jugular deep-vein thrombosis was diagnosed across approximately 2,150 person-days in microgravity. Two astronauts nevertheless developed reversed flow in the left jugular vein. Those findings prompted additional examinations and specialist discussion, but not a clot diagnosis. The investigators explicitly cautioned that, because no thrombosis occurred in their sample, the relationship between the measured flow abnormalities and thrombosis remained uncertain. An unusual image or flow pattern was therefore not interchangeable with a confirmed clot. The surveillance paper also described practical limits to comparing the measurements. Some terrestrial baseline examinations took place after flight rather than before it. Astronauts operated their own ultrasound probes in orbit with real-time guidance from the ground, introducing potential variation in probe position, pressure and angle. Differences in equipment and settings could also affect the images. The authors recommended greater standardization. Their findings supported continued surveillance, while leaving substantial uncertainty about which abnormalities reliably identify a higher-risk individual. An ESA-supported expert review published in npj Microgravity in 2023 put these observations within a wider research agenda covering mechanisms, risk, diagnosis and management. It discussed the limited spaceflight evidence and uncertainty over whether physiological changes translate into increased thrombosis risk. The review did not establish a definitive incidence rate for future missions. Read alongside the earlier studies, it explains the research context for NASA's new request without turning historical observations into a new clinical result or a proven preventive strategy.