VTE — COVID-19 Thromboprophylaxis (ASH 2025)

Personal study digest, pitched for IM boards / a rising heme-onc fellow. Recommendations carry the guideline’s GRADE strength (all conditional) and certainty. Scope: this ASH 2025 release addresses only COVID-19 thromboprophylaxis in adults. The routine adult DVT/PE treatment standard is ASH 2020 (Ortel). The other guideline in this queue slot — the ASH/ISTH 2025 pediatric VTE guideline — is out of scope for an adult IM/ID audience and is intentionally not digested. The “What’s changed / context” section is reviewer synthesis, each claim cited.

In one line

Hospitalized COVID-19, no VTE: escalate to therapeutic-intensity heparin on the ward (acutely ill) but NOT in the ICU (critically ill), and skip routine post-discharge prophylaxis. The counterintuitive part — the sicker (ICU) patient gets less anticoagulation. All recommendations are conditional, very-low certainty.

Two buckets — define them first

Critically ill = immediately life-threatening COVID-19 needing ICU-level support (vasopressors, mechanical ventilation, RRT). Not an incidental positive admitted to ICU for another reason.
Acutely ill = ward admission without intensive support (e.g., dyspnea, mild-to-moderate hypoxia).

How intensely do you anticoagulate?

Setting	ASH 2025 suggests	Strength
Critically ill (ICU)	Prophylactic-intensity — over both intermediate and therapeutic	Conditional
Acutely ill (ward)	Therapeutic-intensity over prophylactic; and prophylactic over intermediate	Conditional
Post-discharge	Against routine outpatient thromboprophylaxis	Conditional

Key decisions the fellow owns

Agent: LMWH or UFH (the trials used them). No high-intensity data for fondaparinux, argatroban, bivalirudin, or DOACs in this setting.
Does not apply to anticoagulation of extracorporeal circuits (ECMO, CRRT) or to anyone with a separate anticoagulation indication.
Individualize by thrombosis vs bleeding risk. A thrombosis RAM (e.g., IMPROVE-DD) is externally validated in COVID; no bleeding RAM is validated in COVID.
Post-discharge exception: may be reasonable for high thrombotic + low bleeding risk — the enriched group in the MICHELLE trial — but not routine.

What’s changed / context

Reviewer synthesis to place this narrow COVID-thromboprophylaxis release in the wider adult VTE landscape — each claim cited. Not guideline text.

This is NOT the adult DVT/PE treatment guideline. Routine adult VTE treatment (DOAC first-line; ~3 months for provoked, extended if unprovoked and low bleeding risk) remains ASH 2020 Blood Adv 2020; PMID 33007077. Read this document as a COVID sub-question, not a new adult standard.
Why the ICU/ward split. It tracks the multiplatform RCTs: therapeutic heparin improved outcomes in the noncritically ill NEJM 2021; 10.1056/NEJMoa2105911 but not the critically ill, in whom it added bleeding without benefit NEJM 2021; 10.1056/NEJMoa2103417 (ATTACC / ACTIV-4a / REMAP-CAP). ASH’s COVID guideline has now concluded its “living” phase.
Post-discharge basis. The “reasonable exception” leans on MICHELLE — post-discharge rivaroxaban in high-risk (IMPROVE-DD–selected) COVID patients Lancet 2022; PMID 34921756. Routine use is still not recommended.
Frontier — Factor XI inhibitors. Abelacimab is in phase 3 for cancer-associated VTE (ASTER vs apixaban; MAGNOLIA vs dalteparin). As of this review these are ongoing without a verified practice-changing readout — do not quote a result yet.
Reversal caveat. For life-threatening factor-Xa-inhibitor bleeding, andexanet alfa was withdrawn from the US market (Dec 2025); 4-factor PCC is now the US default per 2026 NEJM reversal review — confirm.

Recency-sensitive — confirm before quoting as current

This ASH 2025 guideline postdates my training cutoff; its DOI/PMID and every currency trial (multiplatform, MICHELLE, ASH 2020) were PubMed/web-verified this run.
Abelacimab ASTER / MAGNOLIA — ongoing; verify current readout status before citing a result.
Andexanet alfa US withdrawal (Dec 2025) — from the deck’s 2026 NEJM reversal review; confirm against current labeling.

Anki cards minted this run (2)

COVID-19 inpatient anticoagulation intensity — ward → therapeutic, ICU → prophylactic (multiplatform trials).
ASH 2025 against routine post-discharge COVID thromboprophylaxis (MICHELLE exception).

Scope note: the ASH/ISTH 2025 pediatric VTE guideline queued alongside this topic was excluded as out-of-scope for the IM-boards/adult audience; no pediatric cards were minted.

Sources: ASH 2025 living guidelines on anticoagulation for thromboprophylaxis, COVID-19 (Blood Adv 2025; DOI 10.1182/bloodadvances.2024014219; PMID 39437797) — local verbatim capture · Multiplatform noncritically ill (NEJM 2021; 10.1056/NEJMoa2105911) & critically ill (NEJM 2021; 10.1056/NEJMoa2103417) · MICHELLE (Lancet 2022; PMID 34921756) · ASH 2020 adult VTE treatment (Blood Adv 2020; PMID 33007077).