Background Hospital-acquired venous thromboembolism (VTE) is a major cause of morbidity and mortality, but thromboprophylaxis can lead to adverse effects. Risk assessment models have therefore been developed to identify patients at risk for VTE who would most benefit from thromboprophylaxis. Two widely adopted risk scores, Padua and IMPROVE, each incorporate more than ten clinical factors, including immobility, which is a well-established and modifiable risk factor for VTE. However, these risk tools reduce mobility to a single yes-or-no question. Collapsing a complex physiologic continuum, such as mobility, into a yes-or-no item overlooks a sizable proportion of patients who have varying and dynamic levels of mobility, ranging from complete bed rest to full mobility.Recent guideline updates have acknowledged this gap and encourage “more accurate mobility assessment,” but no large study has quantified how graded movement affects VTE risk in everyday care. The Johns Hopkins Highest Level of Mobility (JH-HLM) scale, is a reliable and validated tool that spans eight discrete mobility milestones, from lying in bed to walking more than 250 feet, and is assessed multiple times per day over the course of hospitalization. We sought to examine whether thrombotic risk would rise in a graded fashion as mobility decreased.

Methods We performed a retrospective cohort study of adult medicine admissions to two large academic hospitals within the Johns Hopkins Health System (January 2021–April 2024). For each encounter, we averaged the highest JH-HLM scores recorded during any three consecutive days within the first three hospital days, mirroring the Padua “three-day bedrest” window. JH-HLM is scored each shift by nurses and on each rehab therapist encounter to reflect the maximum mobility level they observed the patient perform. Newly diagnosed lower VTEs were confirmed by manual chart review. VTE incidence (events per 1,000 patient-days) and adjusted relative risks (RRs) were estimated with quasi-Poisson models controlling for age, sex, race, body-mass index, comorbidities, individual Padua items, and use of prophylactic anticoagulation. As a sensitivity analysis, we also repeated all analyses using four- and five-day averaging windows of mobility levels.

Results Among 25,763 medical admissions (mean age 61 years; 50% men; 43% Black), 169 patients (0.66%) developed a new VTE. Compared with those who did not experience VTE, cases were older (65 vs 61 years), carried more comorbidities (7.0 vs 5.1), had higher Padua scores (2.3 vs 2.0), and experienced longer stays (23.3 vs 10.1 days). Mobility exposure spanned the full JH-HLM mobility scale: 23% of person-days were at level 8 (>250 ft walked), 28% at level 6 (<25 ft), 18% at level 4 (pivot transfer), and 13% at level 1 (bed-bound). VTE incidence rose smoothly from 0.5 to 1.5 events per 1,000 patient-days across JH-HLM levels 8 to 1; each one-step drop in mobility increased VTE risk by approximately 15% (p-trend < 0.001). Relative to patients who walked >250 ft (JH-HLM=8), those walking <25 ft (JH-HLM=6) had a 1.4-fold higher risk (RR 1.4, 95% CI 1.4–1.4), patients limited to transfers (JH-HLM=4) had a 1.9-fold risk (RR 1.9, 95% CI 1.9–1.9), and bed-bound patients (JH-HLM=1) faced a tripled risk (RR 3.0, 95% CI 2.9–3.1). Sensitivity analyses using four- and five-day mobility windows produced virtually indistinguishable gradients.

Conclusions In this large, diverse cohort, every measurable drop in early-stay mobility level translated into an increase in VTE risk, exposing the limitations of current binary mobility questions in risk assessment tools. Embedding graded scores, such as JH-HLM, into electronic risk calculators could refresh VTE estimates in real-time, nudge clinicians when a patient's movement declines, and direct preventive therapy to those who need it most.

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2025
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