In April 2026, NASA’s Office of the Chief Health and Medical Officer (OCHMO) convened a working group to assess recent VTE case data, analyze new findings on blood‑flow changes observed among astronauts, and evaluate ongoing research and clinical efforts aimed at reducing VTE risk in spaceflight. This initiative will inform updated, evidence‑based clinical practice recommendations.
The following is a summary of the working group’s recommendations:
- The working group concluded that stasis in the left internal jugular vein (IJV) is regarded as the principal risk factor for VTE in microgravity; however, ongoing debate persists concerning the relative influence of reduced flow dynamics, endothelial vulnerabilities, and retrograde flow.
- Limitations of current in‑flight ultrasound technology for precisely quantifying stasis and slow flow were highlighted, particularly when reliance on stasis alone to trigger prophylactic measures.
- Further evaluation of in‑flight ultrasound methods for assessing stasis was recommended.
- Following additional deliberations, the majority of the panel agreed that both stasis and retrograde flow should trigger prophylactic treatment.
- The working group also advised that all additional risk factors beyond stasis be considered when determining the need for prophylaxis.
- Drawing on a comprehensive literature review and panel input, the group developed a VTE Risk Score for Astronauts algorithm. This algorithm recommends initiating anticoagulation prophylaxis for isolated stasis or for combinations of other thrombosis risk factors, each weighted according to terrestrial research findings.
NASA had previously assembled a working group in October 2024 following the diagnosis of venous thromboembolisms (VTEs) among astronauts aboard the International Space Station. Panel members examined case data, revised clinical practice guidelines, and explored potential etiologies.