Summary

ASH 2018 evidence-based guidelines on VTE prevention in hospitalized and nonhospitalized medical patients, including acutely ill inpatients, critically ill inpatients, chronically ill/long-term care residents, outpatients with minor provoking factors, and long-distance travelers. Nineteen GRADE-based recommendations address pharmacologic vs mechanical prophylaxis, agent selection (UFH, LMWH, fondaparinux, DOACs, aspirin), duration, and post-discharge extension. Strong recommendations include pharmacologic prophylaxis for acutely/critically ill inpatients at acceptable bleeding risk, LMWH over DOACs in hospital, and against extended outpatient prophylaxis after discharge.

Key Recommendations

In acutely ill medical inpatients, use LMWH or fondaparinux over UFH for pharmacologic VTE prophylaxis; any parenteral anticoagulant is preferred over none.
In critically ill medical patients, use UFH or LMWH for VTE prophylaxis (strong); prefer LMWH over UFH (conditional).
Pharmacologic VTE prophylaxis is preferred over mechanical prophylaxis when bleeding risk is acceptable in acutely or critically ill medical patients.
When pharmacologic prophylaxis is contraindicated (unacceptable bleeding risk), use mechanical prophylaxis (pneumatic compression devices or graduated compression stockings) rather than no prophylaxis.
Do not routinely combine mechanical plus pharmacologic prophylaxis — use either alone.
In acutely ill hospitalized medical patients, use LMWH rather than DOACs for inpatient prophylaxis (strong).
Do not extend pharmacologic VTE prophylaxis (LMWH or DOAC) beyond hospital discharge in acutely or critically ill medical patients (strong).
Do not routinely give VTE prophylaxis to chronically ill or nursing home patients, or to outpatients with minor provoking factors (immobility, minor injury, infection).
In long-distance travelers (>4 hours) without VTE risk factors, do not use graduated compression stockings, LMWH, or aspirin.
In long-distance travelers at substantially increased VTE risk (recent surgery, prior VTE, postpartum, active malignancy, ≥2 risk factors), use graduated compression stockings or prophylactic LMWH; use aspirin only if LMWH/stockings are not feasible.
Integrate validated VTE and bleeding risk assessment models (e.g., Padua, IMPROVE VTE, IMPROVE bleeding) into prophylaxis decisions.
Recommendations on pharmacologic prophylaxis apply to acutely ill medical patients with stroke.

Thresholds & Doses

Padua Prediction Score ≥4 = high VTE risk (11% VTE incidence without prophylaxis vs 0.3% if score 0-3); prophylaxis indicated at ≥4.
IMPROVE VTE score: 0-1 (0.5% VTE) = low risk; 2-3 (1.5%) = moderate; ≥4 (5.7%) = high; prophylaxis indicated at score ≥2.
IMPROVE bleeding score ≥7 indicates high bleeding risk (favor mechanical over pharmacologic prophylaxis).
Long-distance travel defined as >4 hours for trigger to consider prophylaxis in high-risk travelers.
Major IMPROVE bleeding risk components: active gastroduodenal ulcer (4.5 pts), bleeding within 3 months (4 pts), platelets <50 × 10⁹/L (4 pts), age ≥85 y (3.5 pts), GFR <30 mL/min/m² (2.5 pts), hepatic failure INR >1.5 (2.5 pts), ICU stay (2.5 pts).
Major IMPROVE VTE risk components (Padua): previous VTE, active cancer, reduced mobility, known thrombophilia each 3 pts; trauma/surgery <1 mo 2 pts; age >70 y, heart/respiratory failure, MI/stroke 1 pt each.
Baseline VTE risks used in modeling: PE 0.1-0.4%; proximal DVT 0.2%; distal DVT 0.6-1.4%.
Major bleeding ARR thresholds: DOAC vs LMWH inpatient — RR 1.70 (ARI 2-8 per 1000); extended DOAC — RR 1.99 (ARI 4-12 per 1000).

Citations

Recommendations 1-3 — pharmacologic prophylaxis choice (LMWH/fondaparinux over UFH) in acutely ill medical patients
Recommendations 4-5 — UFH or LMWH (LMWH preferred) in critically ill medical patients
Recommendations 6-10 — mechanical vs pharmacologic prophylaxis and device choice
Recommendations 11-12 — LMWH over DOACs inpatient; no extended DOAC after discharge
Recommendations 13-14 — inpatient-only over extended-duration prophylaxis in acutely and critically ill patients
Recommendations 15-16 — against routine prophylaxis in chronically ill/nursing home and minor-risk outpatients
Recommendations 17-19 — long-distance travel prophylaxis (>4 h) stratified by VTE risk
Table 1 — Padua, IMPROVE VTE, and IMPROVE bleeding risk assessment models with point values and risk thresholds