Why use it

VTE is the third most common cardiovascular complication in hospitalized medical patients, occurring in approximately 1–2% of admissions. The IMPROVE VTE Risk Score provides an evidence-based, validated tool for identifying medically ill patients at high risk of VTE who should receive pharmacological thromboprophylaxis (LMWH, fondaparinux, or DOACs), while avoiding unnecessary anticoagulation — and associated bleeding risk — in low-risk patients. It is endorsed by ISTH and referenced in ASH VTE prophylaxis guidelines.

About

The IMPROVE (International Medical Prevention Registry on Venous Thromboembolism) VTE Risk Score was developed by Spyropoulos and colleagues from a large international registry of medically ill hospitalized patients to predict the 3-month risk of symptomatic VTE (DVT and/or pulmonary embolism). The score was derived from 15,156 patients across 52 hospitals in 12 countries and validated in a separate cohort. It uses 8 pre-specified clinical risk factors, each weighted differently, to generate a total risk score. Unlike the Padua Prediction Score (which uses equal weights), the IMPROVE score uses a weighted regression model that provides a more granular risk stratification. A score ≥2 identifies patients at high risk for VTE who may benefit from pharmacological thromboprophylaxis. The score is particularly useful in settings where VTE prophylaxis decisions are complex due to competing bleeding risks.

When to use

At admission of any medically ill patient to determine VTE prophylaxis need
Reassessment when clinical status changes (e.g., new immobilization, ICU transfer, new cancer diagnosis)
Deciding between pharmacological and mechanical VTE prophylaxis in patients at intermediate risk
Guiding thromboprophylaxis decisions when bleeding risk must be weighed against VTE risk
Used in conjunction with the IMPROVE Bleeding Risk Score to make balanced risk-benefit decisions

Formula

IMPROVE VTE Risk Score: Previous VTE: +3 points Known thrombophilia: +2 points Lower limb paralysis: +2 points Active cancer: +2 points Immobilized ≥7 days (before or expected during hospitalization): +1 point ICU/CCU admission: +1 point Age ≥60 years: +1 point Total: 0–12 Risk Categories: Score <2: Low risk — VTE rate ~0.4% Score ≥2: High risk — VTE rate ~3.2% Score ≥4: Very high risk — VTE rate may exceed 5% Pharmacological thromboprophylaxis recommended for score ≥2 if bleeding risk acceptable.

Pearls & pitfalls

The IMPROVE score threshold of ≥2 identifies the high-risk group — this translates to approximately 3× higher VTE rate compared to low-risk patients.
Previous VTE is the strongest individual predictor and contributes the most points (3 points) — always document prior VTE history on admission.
Known thrombophilia (antiphospholipid syndrome, Factor V Leiden, prothrombin gene mutation, protein C/S deficiency, antithrombin deficiency) adds 2 points — ask specifically about clotting disorders.
Immobility for ≥7 days (either before or anticipated during hospitalization) adds 1 point — re-evaluate daily if mobility status changes.
The IMPROVE score should ideally be used alongside the IMPROVE Bleeding Risk Score — high VTE risk must be balanced against bleeding risk before prescribing anticoagulation.
ICU/CCU stay adds only 1 point to the IMPROVE score, but ICU patients often have multiple additional risk factors that accumulate.
Age ≥60 years adds 1 point — the effect of age is modest in isolation but compounds with other risk factors.
Cancer adds 2 points and is one of the strongest modifiable risk contexts — cancer patients with hospitalization warrant aggressive VTE prophylaxis unless actively bleeding.
The score does NOT include surgical patients — use Caprini Score for surgical VTE risk assessment.
Extended thromboprophylaxis (beyond hospital stay) with betrixaban or rivaroxaban may be considered for high-risk IMPROVE patients who remain mobility-impaired after discharge.

Next steps

Score <2 (Low Risk): VTE risk <0.5%. Mechanical prophylaxis (compression stockings or IPC) if no contraindication. Pharmacological prophylaxis generally not indicated. Early ambulation. Score ≥2 (High Risk): VTE risk ≥3.2%. Pharmacological thromboprophylaxis indicated if bleeding risk acceptable — LMWH (enoxaparin 40 mg SC daily, or weight-based), fondaparinux 2.5 mg SC daily, or DOAC (betrixaban or rivaroxaban per approved indication). Calculate IMPROVE Bleeding Risk Score before prescribing anticoagulation. Score ≥4 (Very High Risk): VTE risk may exceed 5%. Ensure pharmacological prophylaxis is in place unless absolute contraindication.

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. Derivation: 15,156 patients (IMPROVE registry, 52 hospitals, 12 countries). Validation in independent IMPROVE cohort. Score ≥2: VTE rate 3.2% vs 0.4% (Score <2), OR 7.2. Rosenberg DJ et al. Development of the risk of symptomatic VTE (IMPROVE) score. TH Open. 2017;1(1):e68-e75.

References

Spyropoulos AC et al. Predictive and associative models to identify hospitalized medical patients at risk for VTE. Chest. 2011;140(3):706-714. — link
Rosenberg DJ et al. Development of the risk of symptomatic VTE (IMPROVE) score. TH Open. 2017;1(1):e68-e75. — link
Leizorovicz A et al. Randomized, placebo-controlled trial of dalteparin for the prevention of venous thromboembolism in acutely ill medical patients. Circulation. 2004;110(7):874-879. — link
Cohen AT et al. Extended thromboprophylaxis with betrixaban in acutely ill medical patients. N Engl J Med. 2016;375(6):534-544. — link

IMPROVE Risk Score for VTE

Calculator