National Institutes of Health Funding for Venous Thromboembolism Research

Venous thromboembolism (VTE) is associated with approximately 100,000 deaths annually in the United States (U.S.). Progress in the prevention, diagnosis, treatment, and recovery of VTE depends on research funding. The National Institutes of Health (NIH), the world’s largest funder of biomedical research, does not currently report VTE-specific funding in its annual categorical spending report. This study aimed to provide a descriptive analysis of NIH funding for VTE research over the past decade and compare it to funding for other leading causes of vascular mortality.

We conducted a search within the NIH RePORTER database for the years 2015 to 2024 using a string of VTE-related search terms. Grants were categorized as VTE research (yes/no) for each funding year using a large language model (LLM) prompted with predefined classification criteria. Interrater reliability between the LLM categorization and categorization by two independent human reviewers was estimated using Fleiss’ kappa for FY2015. We tabulated annual NIH funding amounts, the number of VTE-related grants, and unique principal investigators. For 2023, the VTE research investment was compared to funding for heart disease and stroke, the leading causes of vascular mortality in the U.S.

The search yielded 2,130 grants with complete data, of which 1,114 were classified as VTE research. Fleiss K for interrater reliability comparing grant categorization for FY2015 by the LLM and two independent human reviewers was 0.71 (95%CI 0.62-0.80) indicating good inter-rater agreement. When excluding renewal awards, 490 unique VTE grants were identified. Total inflation-adjusted NIH funding for VTE research was $42 million in 2015, peaked at $73 million in 2021, and totaled $67.1 million in 2024. The R01 mechanism accounted for 460 (41.3%) of total awards, while mentored K awards accounted for 83 (7.5%) of total awards. Inflation-adjusted funding for mentored K awards increased more than 3-fold over the study period from $623K in 2015 to $2.3 million in 2024. When adjusted for the number of annual deaths, the NIH investment amounted to approximately $2,765 per death for heart disease, $2,724 for stroke, and $639 for VTE.

The NIH investment in VTE research has increased over the past decade but remains disproportionately low relative to other major causes of vascular mortality in the United States.