IMPROVE Risk Score for VTE

Why use it

VTE is a leading cause of preventable in-hospital and post-discharge morbidity and mortality in medical patients. While surgical patients routinely receive thromboprophylaxis, pharmacological prophylaxis in medical patients carries bleeding risks that must be balanced against VTE risk. The IMPROVE score provides a structured, evidence-based framework for this decision — identifying patients at sufficient VTE risk to justify the bleeding risk of anticoagulation, and those where prophylaxis may be unnecessary or harmful.

About

The IMPROVE (International Medical Prevention Registry on Venous Thromboembolism) VTE Risk Score is a validated clinical prediction tool developed to stratify the risk of venous thromboembolism (VTE) — including deep vein thrombosis (DVT) and pulmonary embolism (PE) — in acutely ill hospitalized medical patients. Derived from a multicenter prospective registry of over 15,000 hospitalized medical patients across 52 hospitals in 12 countries, the IMPROVE score uses 7 clinical risk factors weighted by their contribution to VTE risk. The tool helps identify patients who would benefit from pharmacological thromboprophylaxis (LMWH, fondaparinux, or UFH) and distinguishes them from lower-risk patients where mechanical prophylaxis (TED stockings, IPC devices) alone may suffice. The score has been validated in multiple independent cohorts and is endorsed by CHEST and ISTH guidelines for risk stratification in hospitalized medical patients.

When to use

• At admission for all acutely ill hospitalized medical patients (non-surgical) to assess VTE risk
• When deciding between pharmacological vs. mechanical thromboprophylaxis in medical inpatients
• In patients where LMWH thromboprophylaxis is being considered — combine with IMPROVE Bleeding Risk Score to assess net clinical benefit
• For post-discharge extended thromboprophylaxis planning (betrixaban or rivaroxaban approved in US for extended prophylaxis in high-risk medical patients)
• Clinical quality improvement programs for VTE prevention in hospitalized patients

Formula

Pearls & pitfalls

• The IMPROVE score should be used in CONJUNCTION with the IMPROVE Bleeding Risk Score — always assess both VTE risk and bleeding risk before initiating pharmacological prophylaxis.
• Previous VTE carries the highest individual weight (3 points) — a prior DVT or PE is the strongest single predictor of in-hospital recurrent VTE.
• Known thrombophilia (2 points) includes factor V Leiden, prothrombin gene mutation, antiphospholipid antibody syndrome, protein C/S deficiency, and antithrombin deficiency.
• Current lower-limb paralysis (2 points) includes any acute lower limb paresis or plegia — major stroke, spinal cord injury, or acute neuromuscular disease.
• ICU/CCU admission is a key institutional risk factor — critically ill patients have dramatically higher VTE incidence than general medical ward patients.
• The IMPROVE score was derived in the era before routine pharmacological prophylaxis — contemporary absolute VTE rates in patients already on prophylaxis will be lower.
• Renal impairment affects LMWH dosing: CrCl <30 mL/min requires dose reduction (enoxaparin 20 mg once daily) or use of UFH; CrCl <15 mL/min → UFH preferred.
• Extended post-discharge thromboprophylaxis is supported by MARINER (rivaroxaban) and APEX (betrixaban) trials in patients with IMPROVE ≥4 and elevated D-dimer.

Next steps

IMPROVE <2 (Low Risk): VTE risk <0.5%. Mechanical prophylaxis (IPC or TED stockings) if appropriate. Early mobilization encouraged. Pharmacological prophylaxis not routinely indicated. IMPROVE 2–3 (Moderate Risk): VTE risk ~1.4%. Consider pharmacological prophylaxis if bleeding risk is low (assess with IMPROVE Bleeding Risk Score). LMWH (enoxaparin 40 mg SC once daily; reduce to 20 mg if CrCl 15–30 mL/min) or UFH (5,000 units SC every 8–12h). IMPROVE ≥4 (High Risk): VTE risk ~4–7%. Pharmacological prophylaxis recommended in all patients without contraindication. LMWH preferred over UFH. Consider extended prophylaxis post-discharge in eligible patients (betrixaban 80 mg once daily × 35–42 days, or rivaroxaban 10 mg once daily × 31–39 days, if approved and indicated).

Evidence

Spyropoulos AC et al. Predictive and associative models to identify hospitalized medical patients at risk for VTE. Chest. 2011;140(3):706-714. PMID:21436241. Derived from IMPROVE registry (n=15,156 patients). Validated in multiple cohorts. VTE rates: score <2: 0.4%, 2–3: 1.5%, ≥4: 4.0%. APEX trial (betrixaban) and MARINER trial (rivaroxaban) used IMPROVE ≥4 as inclusion criterion for extended prophylaxis. ACCP 2012 and ISTH 2016 guidelines endorse IMPROVE for VTE risk stratification.

References

1. Spyropoulos AC et al. Predictive and associative models to identify hospitalized medical patients at risk for VTE. Chest. 2011;140(3):706-714. — link
2. Cohen AT et al. Extended thromboprophylaxis with betrixaban in acutely ill medical patients (APEX). N Engl J Med. 2016;375(6):534-544. — link
3. Spyropoulos AC et al. Rivaroxaban for Thromboprophylaxis after Hospitalization for Medical Illness (MARINER). N Engl J Med. 2018;379(12):1118-1127. — link
4. Kahn SR et al. Prevention of VTE in nonsurgical patients: antithrombotic therapy and prevention of thrombosis, 9th ed: ACCP evidence-based clinical practice guidelines. Chest. 2012;141(2 Suppl):e195S-226S. — link