Anticoagulation Management
Warfarin vs DOACs vs heparin: choosing, dosing, monitoring, bridging, and reversal. The most commonly consulted hematology topic on wards.
🔍 Overview
Overview
Anticoagulation management is one of the most common daily tasks on inpatient medicine. Key decisions: (1) Which agent? Heparin (UFH for acute, can titrate, dialyzable) vs LMWH (predictable, SQ, no monitoring) vs warfarin (outpatient, INR monitoring, cheap) vs DOAC (outpatient, no monitoring, fewer interactions, not all indications). (2) When to bridge? Only high-risk patients (mechanical valve, recent VTE < 3 months, prior thrombosis on interruption). (3) How to reverse? Warfarin: vitamin K ± 4-factor PCC. DOACs: idarucizumab (dabigatran), andexanet alfa (Xa inhibitors), or 4F-PCC. Heparin: protamine. Key intern skill: recognizing bleeding vs thrombotic risk and adjusting therapy accordingly.
Warfarin-only indications (DOACs are contraindicated): (1) Mechanical heart valves - RE-ALIGN, 2013 showed excess valve thrombosis with dabigatran. (2) Triple-positive antiphospholipid syndrome - TRAPS, 2018 showed excess arterial events with rivaroxaban. (3) Moderate-severe (rheumatic) mitral stenosis - INVICTUS, 2022 showed warfarin superior to rivaroxaban with lower mortality. For ALL other indications (nonvalvular AF, VTE), DOACs are preferred over warfarin.
Key distinction: the warfarin mandate is for rheumatic moderate-severe MS specifically, not any severe MS. The cause matters, not just the severity. Non-rheumatic severe MS (e.g., calcific MS from mitral annular calcification in the elderly) is not a DOAC contraindication, because it lacks the thrombogenic rheumatic left-atrial substrate INVICTUS studied; a DOAC is reasonable there (data are limited, so individualize if the LA is markedly enlarged/stagnant).
Key distinction: the warfarin mandate is for rheumatic moderate-severe MS specifically, not any severe MS. The cause matters, not just the severity. Non-rheumatic severe MS (e.g., calcific MS from mitral annular calcification in the elderly) is not a DOAC contraindication, because it lacks the thrombogenic rheumatic left-atrial substrate INVICTUS studied; a DOAC is reasonable there (data are limited, so individualize if the LA is markedly enlarged/stagnant).
When to choose each anticoagulant: UFH = acute (titratable, reversible, dialyzable). LMWH = predictable SQ dosing, cancer VTE. Warfarin = mechanical valve, APS, severe CKD (CrCl < 15), cost. DOAC = everything else (AF, VTE) - fewer interactions, no monitoring, rapid onset. Fondaparinux = HIT with VTE (no heparin cross-reactivity).
🧪 Workup
Workup
- Before starting anticoagulation: CBC, PT/INR, aPTT, Cr + CrCl (DOAC renal dosing), LFTs (hepatic clearance), HAS-BLED score (bleeding risk)
- Warfarin monitoring: INR (target 2-3 for most indications; 2.5-3.5 for mechanical mitral valve). Check INR daily inpatient until stable, then q1-4 weeks outpatient.
- Heparin monitoring: aPTT q6h after initiation or dose change (anti-Xa levels if aPTT unreliable -lupus anticoagulant, elevated baseline). Target aPTT per institutional protocol (usually 1.5-2.5× control).
- LMWH: No routine monitoring. Check anti-Xa level (peak, 4h post-dose) if: obesity (> 150 kg), CKD (CrCl < 30 → use UFH instead), pregnancy.
- DOACs: No routine monitoring. Check Cr + CrCl (dose-adjust apixaban/rivaroxaban at CrCl 15-30; dabigatran CI if CrCl < 30). Drug-specific anti-Xa (rivaroxaban, apixaban) or dTT (dabigatran) for special situations (overdose, pre-surgery, bleeding).
- Indication verification: AF (CHA₂DS₂-VASc ≥ 2 men, ≥ 3 women), VTE treatment, mechanical valve (warfarin only), antiphospholipid syndrome (warfarin preferred over DOACs TRAPS, 2018)
🚨 Management
Management
- VTE treatment: DOAC preferred (rivaroxaban or apixaban). Duration: provoked DVT = 3 months; unprovoked = extended (reassess annually). Cancer-associated VTE: LMWH or DOAC (edoxaban, rivaroxaban) [HOKUSAI VTE Cancer, 2018; SELECT-D, 2018]. Exception: GI/GU cancer with high bleed risk → LMWH preferred.
- AF anticoagulation: DOAC preferred over warfarin for nonvalvular AF [RE-LY, ROCKET AF, ARISTOTLE, ENGAGE AF-TIMI 48]. Exception: moderate-severe mitral stenosis or mechanical valve → warfarin only.
Two kinds of bridging. "Bridge" means using a fast parenteral anticoagulant (UFH/LMWH) to cover any window when warfarin is sub-therapeutic -which happens in two settings. (1) Initiation bridging: starting warfarin in someone with an acute clot (new DVT/PE, LV thrombus, new mechanical valve). Overlap heparin/LMWH until INR ≥ 2 for 24h (minimum 5-day overlap), because warfarin takes 5-7 days to work AND is transiently procoagulant in the first few days (protein C and S fall before factors II, IX, X -the same mechanism behind warfarin skin necrosis). (2) Periprocedural bridging: interrupting warfarin for surgery and covering the gap -detailed below. DOACs need neither, since they are immediately therapeutic; the only exception is the 5-day heparin lead-in for edoxaban and dabigatran in VTE.
- Perioperative bridging:
- Most patients: do NOT bridge. BRIDGE, 2015 -bridging with LMWH in AF patients on warfarin increased bleeding without reducing thrombosis.
- Bridge ONLY high thrombotic risk (roughly > 10%/yr off anticoagulation):
- Mechanical valve: ANY mitral mechanical valve; any older caged-ball (Starr-Edwards) or tilting-disc (Björk-Shiley) valve; any mechanical valve + stroke/TIA within 6 months. Why: highest stasis and thrombogenicity, and a periprocedural clot here means valve thrombosis or disabling stroke. Exception: an isolated bileaflet aortic valve (St. Jude, On-X, CarboMedics) with no other risk factors is the one mechanical valve that does NOT need bridging (low-thrombogenicity, high-flow position; see box below).
- AFib: CHA₂DS₂-VASc ≥ 7, stroke/TIA within 3 months, or rheumatic (valvular) AF. Why: recent cardioembolism predicts early recurrence, and rheumatic mitral stenosis carries the highest AF stroke rate.
- VTE: VTE within the last 3 months, or severe thrombophilia (protein C/S deficiency, antiphospholipid syndrome, homozygous factor V Leiden). Why: clot is still organizing and recurrence risk is steepest in the first 3 months.
- Stop warfarin 5 days before. Stop DOAC 2-3 days before (longer if CKD). Resume 24-72h post-procedure depending on bleeding risk.
The only mechanical valve you DON'T bridge: an isolated bileaflet aortic valve (St. Jude, On-X, CarboMedics) with no other risk factors. Why: modern bileaflet design is the least thrombogenic mechanical valve, and the high-flow, low-stasis aortic position drops the off-anticoagulation thromboembolic risk below ~5%/yr (low-risk tier), so the bleeding cost of bridging outweighs the small thrombotic benefit during a brief warfarin hold. It jumps back into bridge-worthy territory with ANY of: AFib, prior stroke/TIA, LV dysfunction, HTN, diabetes, age > 75, or more than one mechanical valve. Every mitral mechanical valve, and every older caged-ball (Starr-Edwards) or tilting-disc (Björk-Shiley) valve, is always bridged.
DOAC perioperative management is simpler than warfarin: No bridging needed. Simply hold the DOAC 24-48h pre-procedure (48-72h if CrCl < 50 or high-bleed-risk surgery). Resume 24-48h post-procedure. The PAUSE trial validated this approach with low rates of both thromboembolism (0.16%) and major bleeding (1.35%). PAUSE, 2019
- Reversal:
- Warfarin: Vitamin K 10 mg IV (takes 6-24h). For urgent: 4-factor PCC (Kcentra) 25-50 units/kg (immediate). FFP only if PCC unavailable.
- Dabigatran: Idarucizumab (Praxbind) 5g IV -immediate, complete reversal. RE-VERSE AD, 2017
- Xa inhibitors (rivaroxaban/apixaban/edoxaban): Andexanet alfa (Andexxa) -expensive, limited availability. Alternative: 4-factor PCC 50 units/kg. ANNEXA-4, 2019
- Heparin: Protamine 1 mg per 100 units UFH given in last 2-3h (max 50 mg). Only 60% effective for LMWH.
Supratherapeutic INR management: INR 4.5-10, no bleeding: hold warfarin, recheck INR in 24-48h. Consider vitamin K 1-2.5 mg PO if high bleeding risk. INR > 10, no bleeding: vitamin K 5-10 mg PO, recheck in 24h. ANY INR + serious/life-threatening bleeding: 4-factor PCC 25-50 U/kg + vitamin K 10 mg IV + hold warfarin. FFP only if PCC unavailable (slower, volume overload).
Red Clot vs White Clot: Matching the Drug to the Thrombus
One rule sets up every triple-therapy decision: fast flow = platelets = antiplatelet; slow flow = fibrin = anticoagulant. Clot composition is dictated by flow physiology (Virchow). Under high arterial shear, von Willebrand factor unfolds and platelets drive the clot; under venous stasis (or a stagnant LA appendage) the coagulation cascade runs to completion and fibrin traps red cells. One drug class cannot cover both, which is exactly why a patient with AF (a fibrin problem) who gets a stent (a platelet problem) transiently needs both.
| Feature | White clot (platelet-rich) | Red clot (fibrin/RBC-rich) |
|---|---|---|
| Location / flow | Arteries: high flow, high shear | Veins + stagnant cardiac chambers: low flow, stasis |
| Trigger | Endothelial injury: plaque rupture/erosion, exposed stent struts | Stasis + hypercoagulability (Virchow's triad) |
| Dominant mechanism | High shear unfolds vWF → platelet adhesion and aggregation; platelet-dominant | Coagulation cascade → thrombin → fibrin mesh that traps RBCs |
| Appearance | Pale, platelet-fibrin plug | Dark red, gelatinous, RBC-laden |
| Rate-limiting step | Platelet activation, so thrombin inhibition alone will not stop it | Fibrin formation, so antiplatelets barely touch it |
| Drug that works | Antiplatelets (aspirin, P2Y12, GP IIb/IIIa) | Anticoagulants (heparin/LMWH, warfarin, DOACs) |
Conditions by clot type (most common first)
| Platelet-rich / arterial → antiplatelet-led | Fibrin-rich / stasis → anticoagulant-led |
|---|---|
| ACS: STEMI, NSTEMI, unstable angina | Atrial fibrillation (LA appendage stasis → cardioembolism) Anticoagulate if CHA₂DS₂-VASc ≥ 2 (men) / ≥ 3 (women); score 1/2 = consider |
| Coronary stent thrombosis prevention (post-PCI) | VTE: DVT and PE Provoked by a transient factor: 3 months. Unprovoked or persistent risk: extended/indefinite (reassess bleeding risk annually) |
| Stable CAD / chronic coronary syndrome | LV thrombus (akinetic segment post-MI) |
| Atherothrombotic (non-cardioembolic) ischemic stroke/TIA | Mechanical heart valves |
| Peripheral arterial disease | Intracardiac thrombus / dilated cardiomyopathy |
Don't cross the streams: AF cardioembolism is fibrin-rich, so an antiplatelet is inferior to an anticoagulant for stroke prevention ACTIVE-W, 2006. Conversely, antiplatelets remain the backbone for stents and ruptured plaque because an anticoagulant alone does not prevent stent thrombosis. Triple therapy exists only for the patient who legitimately has one of each problem at the same time, which is the scenario below.
AF + Recent PCI/ACS: Combining Anticoagulant + Antiplatelet
Triple therapy = oral anticoagulant (OAC) + aspirin + P2Y12 inhibitor (clopidogrel). It is indicated only when one patient simultaneously carries an anticoagulation indication AND a dual-antiplatelet (DAPT) indication, that is, two distinct clot problems at once (red clot + white clot, above). Neither drug class alone covers both, which is why all three are stacked, but only briefly.
| Needs an anticoagulant (the OAC) | ...PLUS needs DAPT (aspirin + P2Y12) |
|---|---|
| AF with elevated stroke risk (CHA₂DS₂-VASc) | PCI with coronary stent (the dominant reason) |
| Recent VTE (DVT/PE) on ongoing anticoagulation Treat ≥ 3 months (provoked by a transient factor) or extended/indefinite (unprovoked or persistent risk). Recurrence is steepest in the first 3 months, the high-risk "recent" window that justifies the overlap. | Acute coronary syndrome: STEMI / NSTEMI |
| Mechanical heart valve (warfarin, not a DOAC) | |
| LV thrombus (akinetic segment post-MI) |
The overlap is the indication: a left-column reason AND a right-column reason in the same patient. The textbook case is AF (left) who undergoes PCI/stenting for ACS (right). Once you have identified that overlap, the entire goal is to spend as little time on triple therapy as possible and de-escalate as below.
Default = double therapy: a DOAC + one P2Y12 inhibitor (clopidogrel), drop aspirin early. Add aspirin (triple therapy) only for the peri-PCI window. Why: AUGUSTUS, 2019 showed that once a DOAC + P2Y12 are on board, aspirin just adds bleeding with no ischemic benefit.
| Phase | Regimen | Why |
|---|---|---|
| Peri-PCI (in-hospital, up to ~1 week) | Triple: DOAC + clopidogrel + aspirin | Stent-thrombosis risk is highest early, so a brief aspirin overlap is justified (longer only if very high ischemic risk). |
| Discharge → ~6-12 months | Double: DOAC + clopidogrel (no aspirin) | Dropping aspirin cuts bleeding while preserving ischemic protection (AUGUSTUS, PIONEER AF-PCI 2016, RE-DUAL PCI 2017). |
| After 12 months | DOAC monotherapy | 2023 AF guideline: stable CAD beyond 1 year → anticoagulant alone; adding any antiplatelet only adds bleeding. |
Agent choices: DOAC preferred over warfarin (apixaban has the strongest evidence here). The P2Y12 of choice is clopidogrel -ticagrelor and prasugrel add bleeding when combined with an anticoagulant and are generally avoided. If warfarin must be used, target INR 2.0-2.5 with a high time-in-range.
Anticoagulation in Pregnancy
LMWH is the anticoagulant of choice in pregnancy -it does not cross the placenta, so there is no teratogenic or fetal-bleeding risk. DOACs are contraindicated and warfarin is avoided, except for the specific mechanical-valve role below.
| Agent | Use in pregnancy | Why |
|---|---|---|
| LMWH (enoxaparin, dalteparin) PREFERRED | First-line for VTE treatment and prophylaxis and for most indications, all trimesters. Weight-based dosing; check anti-Xa in obesity, renal impairment, or mechanical valves. | Does NOT cross the placenta, so no fetal harm. Predictable outpatient SQ dosing, no INR monitoring. |
| UFH | When rapid reversibility is needed (peri-delivery), severe renal failure (CrCl < 30), or in the window just before neuraxial anesthesia. | Also does not cross the placenta. Short half-life and protamine-reversible, which is why it is favored around delivery. |
| Warfarin AVOID (valve exception) | Avoid in general. Retained only for mechanical heart valves in the 2nd and 3rd trimesters (ACC/AHA and ESC class IIa), then switched to LMWH/UFH at ~36 weeks before delivery. | Crosses the placenta → warfarin embryopathy (nasal hypoplasia, stippled epiphyses) at weeks 6-12, plus later fetal CNS injury and intracranial bleeding. But it is the most effective at preventing valve thrombosis, so maternal risk can outweigh fetal risk for mechanical valves. |
| DOACs (apixaban, rivaroxaban, dabigatran, edoxaban) CONTRAINDICATED | Do NOT use in pregnancy (or while breastfeeding). | Cross the placenta; inadequate safety data with signals of fetal harm. No role even in mechanical valves. |
| Fondaparinux | Second-line, only if HIT or LMWH allergy/intolerance. | Minimal placental transfer but limited pregnancy data, so reserved for when heparins cannot be used. |
Mechanical heart valve in pregnancy = highest-risk scenario. Three accepted strategies (shared decision-making): (1) dose-adjusted LMWH throughout (BID to a peak anti-Xa 1.0-1.2 IU/mL, or TID targeting trough 0.6-0.7); (2) LMWH in the 1st trimester (weeks 6-12, to avoid embryopathy) then warfarin in the 2nd/3rd; or (3) warfarin throughout if the required dose is low (≤ 5 mg/day carries the lowest fetal risk). Switch to UFH/LMWH at ~36 weeks so the fetus is not warfarin-anticoagulated during delivery. ESC, 2025
Delivery and breastfeeding: Hold LMWH ≥ 24h before planned delivery or neuraxial anesthesia (≥ 12h for a prophylactic dose). Warfarin, UFH, and LMWH are all compatible with breastfeeding (not secreted in clinically significant amounts); DOACs are not recommended while breastfeeding.
💊 Medications
Medications
| Warfarin (Coumadin) | Individualized (typically 2-10 mg daily) | PO | Required for mechanical valves + APS. INR monitoring. Drug/food interactions. Vitamin K dependent factors (II, VII, IX, X, protein C/S). |
| Heparin (UFH) | 80 U/kg bolus → 18 U/kg/hr | IV | Titratable, short half-life, dialyzable. Monitor aPTT q6h. Protamine for reversal. HIT risk. |
| Enoxaparin (Lovenox) | 1 mg/kg BID or 1.5 mg/kg daily | SQ | Predictable pharmacokinetics. Avoid if CrCl < 30 (accumulates). Anti-Xa for monitoring in special populations. |
| 4-Factor PCC (Kcentra) | 25-50 U/kg IV | IV | Warfarin reversal (immediate). Also used off-label for Xa inhibitor reversal. Contains factors II, VII, IX, X + protein C/S. |
DOAC dosing by indication: Apixaban: AF = 5 mg BID (2.5 mg if >= 2 of: age >= 80, weight <= 60 kg, Cr >= 1.5). VTE = 10 mg BID x 7d then 5 mg BID. Rivaroxaban: AF = 20 mg daily WITH FOOD (bioavailability drops 39% without food). VTE = 15 mg BID x 21d then 20 mg daily. Edoxaban: 60 mg daily (30 mg if CrCl 15-50 or weight <= 60 kg). Requires 5-day heparin lead-in. ARISTOTLE, 2011
🩸 HIT
Heparin-Induced Thrombocytopenia (HIT)
HIT is a prothrombotic emergency, not a bleeding problem. IgG antibodies form against platelet factor 4 (PF4)-heparin complexes and activate platelets, causing thrombocytopenia AND thrombosis at the same time. Despite the low platelet count, the danger is clot (venous > arterial, limb gangrene, stroke, MI), not bleeding -so the treatment is MORE anticoagulation, just not with heparin.
When to suspect it: a platelet drop > 50% from baseline (or new thrombosis) 5-10 days after starting heparin. Rapid onset (< 24h) if there was heparin exposure within the prior ~100 days (pre-formed antibodies). More common with UFH > LMWH and in surgical > medical patients.
First exclude pseudothrombocytopenia. EDTA (purple-top) tubes can trigger in-vitro platelet clumping from EDTA-dependent agglutinins, giving a falsely low automated count in a well patient. If the drop is isolated and unexpected, check the peripheral smear for platelet clumps and redraw in a sodium citrate (blue-top) tube -a normal count on the citrate sample confirms a lab artifact, not true thrombocytopenia, and spares an unnecessary HIT workup.
4T Score (pre-test probability)
| Feature | 2 points | 1 point | 0 points |
|---|---|---|---|
| Thrombocytopenia | Fall > 50% AND nadir ≥ 20K | Fall 30-50% or nadir 10-19K | Fall < 30% or nadir < 10K |
| Timing | Day 5-10 (or ≤ 1 day if heparin within 30 days) | > Day 10 or timing unclear | < Day 4, no recent heparin |
| Thrombosis | New thrombosis, skin necrosis, or post-bolus systemic reaction | Progressive/recurrent or suspected thrombosis | None |
| oTher cause | None apparent | Possible | Definite other cause |
0-3 = low (HIT effectively excluded, do not test) · 4-5 = intermediate · 6-8 = high. Send antibody testing only if intermediate or high.
Confirming the Diagnosis
- Step 1, PF4-heparin antibody ELISA (immunoassay): highly sensitive, so a negative result rules HIT out. A positive is less specific (many antibodies are non-pathogenic); a higher optical density makes true HIT more likely.
- Step 2, serotonin release assay (SRA): the functional gold standard, highly specific, confirms pathogenic antibodies. Do not wait for it before acting.
Management
Act on clinical suspicion, do not wait for confirmatory testing.
- STOP all heparin -UFH and LMWH, SQ prophylaxis, line flushes, and heparin-bonded catheters. Why: any heparin keeps fueling antibody-mediated platelet activation.
- Start a non-heparin anticoagulant immediately at therapeutic dose: argatroban (hepatic clearance, use in renal failure), bivalirudin, fondaparinux, or a DOAC (increasingly used for stable HIT). Why: HIT is prothrombotic, so simply stopping heparin is not enough, the clot risk persists for weeks.
- Do NOT start warfarin until platelets recover (> 150K). Why: warfarin acutely drops protein C and triggers venous limb gangrene / skin necrosis in the prothrombotic HIT state. If the patient is already on warfarin, reverse it with vitamin K and overlap a non-heparin agent.
- Do NOT give prophylactic platelet transfusions. Why: it adds fuel to thrombosis; reserve platelets for active bleeding only.
- Duration: anticoagulate 4 weeks for isolated HIT (until platelet recovery) and 3 months if thrombosis occurred (HITT). Document a heparin allergy and avoid re-exposure.
🏥 Rounds
Pimp Questions
❓ When should you bridge anticoagulation perioperatively and when should you not?
Do NOT bridge most patients. BRIDGE, 2015 showed that bridging AF patients on warfarin with LMWH increased major bleeding 3-fold without reducing stroke. Bridge ONLY: mechanical mitral valve, mechanical aortic valve + additional risk factor (AF, prior stroke, EF < 35%), VTE within 3 months, prior thromboembolism during anticoagulation interruption.
❓ Why are DOACs preferred over warfarin for nonvalvular AF?
Four landmark trials showed DOACs are non-inferior or superior to warfarin for stroke prevention with lower rates of intracranial hemorrhage: RE-LY (dabigatran), ROCKET AF (rivaroxaban), ARISTOTLE (apixaban -also reduced mortality), ENGAGE AF (edoxaban). Additional advantages: no INR monitoring, fewer food/drug interactions, predictable pharmacokinetics, rapid onset.
❓ How do you reverse each anticoagulant?
Warfarin: Vitamin K 10 mg IV (slow, 6-24h) + 4-factor PCC 25-50 U/kg (immediate). Dabigatran: Idarucizumab 5g IV (immediate, complete). Xa inhibitors: Andexanet alfa (expensive) or 4F-PCC 50 U/kg (off-label). Heparin: Protamine 1 mg/100 U UFH. LMWH: Protamine partially effective (~60%). For all: hold drug, apply pressure, transfuse if needed.
❓ Why is warfarin preferred over DOACs in antiphospholipid syndrome?
TRAPS, 2018 -trial of rivaroxaban vs warfarin in triple-positive APS was stopped early for excess thrombotic events in the rivaroxaban arm (arterial events). DOACs may be acceptable for single/double-positive APS with venous-only events, but triple-positive APS must be on warfarin. Warfarin is also required for mechanical heart valves (DOACs showed excess valve thrombosis in RE-ALIGN).
❓ What is the CHA₂DS₂-VASc score and when do you anticoagulate?
C HF (1) · H TN (1) · A ge ≥ 75 (2) · D M (1) · S troke/TIA (2) · V ascular disease (1) · A ge 65-74 (1) · S ex female (1). Score 0 (men) or 1 (women): no anticoagulation. Score 1 (men) or 2 (women): consider. Score ≥ 2 (men) or ≥ 3 (women): anticoagulate. DOAC preferred unless valvular AF or APS.
❓ A patient on warfarin has an INR of 8.5 with no bleeding. How do you manage this?
Hold warfarin + give vitamin K 2.5-5 mg PO (oral is preferred over IV for non-bleeding supratherapeutic INR). Recheck INR in 24h. Do NOT give PCC or FFP (no active bleeding). If INR > 10 without bleeding, give vitamin K 5-10 mg PO. Resume warfarin at a reduced dose once INR < 3. Common causes of supratherapeutic INR: drug interaction (antibiotics, amiodarone, azole antifungals), dietary change (decreased vitamin K intake), liver disease, alcohol binge.
❓ What are the absolute contraindications to anticoagulation?
Active life-threatening hemorrhage, hemorrhagic stroke (acute phase), severe uncontrolled hypertension (relative), intracranial hemorrhage, major surgery within 24h, platelet count < 25K (relative at < 50K), active GI bleeding. For patients with both high thrombotic AND high bleeding risk (e.g., recent GI bleed + mechanical valve), consult hematology. An IVC filter may be a temporary bridge if anticoagulation must be held. HAS-BLED score >= 3 = high bleeding risk but is NOT a contraindication to anticoagulation.
❓ When should you use heparin drip vs LMWH vs a DOAC for acute VTE?
Heparin drip: when you need tight control and rapid reversibility - Category E PE (may need tPA), high bleeding risk, renal failure (CrCl < 30), perioperative patients. LMWH: stable VTE, predictable dosing, can discharge on it. DOACs: stable VTE for discharge - apixaban or rivaroxaban need no heparin lead-in (load and go). Edoxaban/dabigatran need 5-day heparin lead-in first. Cancer VTE: LMWH or edoxaban/rivaroxaban (not warfarin). AMPLIFY, 2013
❓ How do you manage a patient on a DOAC who needs emergency surgery?
Check last dose timing. If last dose < 24h ago AND high-risk surgery: consider reversal (idarucizumab for dabigatran, andexanet alfa or 4F-PCC 50 U/kg for Xa inhibitors). If last dose > 24-48h ago: most DOACs are sufficiently cleared for surgery (longer washout if CrCl reduced). For urgent but not emergent surgery: delay 24-48h if possible. Drug-specific half-lives: dabigatran 12-17h, rivaroxaban 5-13h, apixaban 12h, edoxaban 10-14h. All are prolonged in renal impairment. Standard coagulation tests (PT/INR) do NOT reliably reflect DOAC activity.
Clinical Examples
📋 Case 1, Perioperative Bridging Decision
Patient: 72M, on warfarin for mechanical aortic valve (INR target 2.5-3.5), needs elective hip replacement in 5 days. Current INR 3.0.
Key findings: Mechanical valve = high thromboembolic risk. CHA2DS2-VASc not applicable (valvular indication). No prior stroke or TIA. EF 55%.
Management:
- Stop warfarin 5 days pre-op (allow INR to drift to < 1.5)
- Mechanical valve = MUST bridge with therapeutic LMWH (enoxaparin 1 mg/kg BID) when INR < 2
- Hold LMWH 24h before surgery
- Resume warfarin evening of surgery; restart LMWH 24-48h post-op when hemostasis confirmed
- Stop LMWH when INR therapeutic (≥ 2.5 for mechanical valve)
Teaching point: Most AF patients do NOT need bridging. BRIDGE, 2015 showed bridging AF patients increased major bleeding 3-fold without reducing stroke. However, mechanical valves remain an absolute bridging indication due to catastrophic thrombotic risk.
📋 Case 2, DOAC Reversal for Life-Threatening Bleeding
Patient: 78F, on apixaban 5 mg BID for AF, presents with massive upper GI bleed (hematemesis, melena). Hemodynamically unstable.
Key findings: HR 118, BP 82/50. Hgb 6.2 (baseline 11.8). INR 1.3 (misleading on DOACs). Last apixaban dose 4 hours ago. Anti-Xa level 180 ng/mL (supratherapeutic).
Management:
- Hold apixaban immediately
- Reversal: andexanet alfa (Andexxa) IV bolus + infusion if available; otherwise 4-factor PCC 50 U/kg (off-label)
- Transfuse pRBC to Hgb > 7; FFP does NOT reverse DOACs
- Emergent EGD once hemodynamically stabilized
- After bleed resolved: reassess anticoagulation indication and risks vs benefits of resumption
Teaching point: Standard INR does NOT reliably reflect DOAC activity. Anti-Xa levels assess rivaroxaban/apixaban; thrombin time for dabigatran. Andexanet alfa reverses Xa inhibitors but is expensive. 4-factor PCC is the pragmatic alternative. ANNEXA-4, 2019
📋 Case 3, Warfarin-Only Indication in APS
Patient: 34F, triple-positive antiphospholipid syndrome (lupus anticoagulant + anti-cardiolipin + anti-beta2-glycoprotein I), history of DVT + PE at age 28. On rivaroxaban 20 mg daily. Presents with acute left MCA stroke.
Key findings: CT head: no hemorrhage. CTA: left MCA occlusion. Thrombectomy performed. INR 1.1 despite rivaroxaban. Anti-Xa level therapeutic (ruling out non-adherence).
Management:
- This is a treatment failure on a DOAC in triple-positive APS
- Switch to warfarin (INR target 2-3, some experts target 3-4 for arterial events)
- Bridge with UFH drip until INR therapeutic
- DOACs are contraindicated in triple-positive APS
- Lifelong anticoagulation with warfarin - never switch to DOAC
Teaching point: TRAPS, 2018 was stopped early because rivaroxaban had significantly more arterial thrombotic events than warfarin in triple-positive APS. Warfarin is also the only option for mechanical heart valves (RE-ALIGN, 2013 showed excess valve thrombosis with dabigatran).
Sample Presentation
Mr. Davis is a 74-year-old man on warfarin for mechanical aortic valve (INR target 2.5-3.5) admitted for cholecystectomy. Current INR 3.1. Surgery planned in 3 days. Question: how do you manage his anticoagulation perioperatively?
Key Points: Mechanical valve = high thromboembolic risk → bridge with therapeutic LMWH. Stop warfarin now (5 days pre-op). Start enoxaparin 1 mg/kg BID when INR < 2. Hold LMWH 24h pre-surgery. Restart heparin drip post-op when hemostasis confirmed (12-24h). Resume warfarin evening of surgery. Stop heparin when INR therapeutic.
Monitoring
- Warfarin INR: daily inpatient → weekly → q2-4 weeks when stable. Time in therapeutic range (TTR) target > 65%.
- Heparin aPTT: q6h after initiation or dose change until 2 consecutive values in range, then q12-24h.
- DOACs: Cr annually (more frequent if CKD). No routine drug levels. CBC at baseline + annually.
- Bleeding assessment: signs (hemoglobin drop, melena, hematuria, bruising), drug interactions (NSAIDs, antiplatelets, CYP3A4 inhibitors)
- HIT screening: platelet count q2-3 days on UFH × first 14 days. 4T score if platelet drop.
- CHA₂DS₂-VASc reassessment: annually for AF patients -score can change (new DM, HF, age threshold).
📋 Summary
Summary
Match the Drug to the Clot
Red clot, fibrin- and red-cell-rich, forms in low-flow venous systems and the fibrillating atrium, and is treated with anticoagulants. White clot, platelet-rich, forms in high-shear arterial vessels and on ruptured plaque, and is treated with antiplatelets. Using the wrong class is a common and consequential error: aspirin does not treat a DVT, and warfarin does not prevent stent thrombosis.
DOACs Are the Default, With Named Exceptions
Preferred for atrial fibrillation and for VTE: fixed dosing, no routine monitoring, fewer interactions, less intracranial hemorrhage. Use warfarin instead for mechanical valves, moderate-to-severe mitral stenosis, and antiphospholipid syndrome (TRAPS showed rivaroxaban inferior). Also use caution in severe renal impairment, extremes of body weight and pregnancy.
Get the DOAC Dose Reduction Right
Each agent has its own criteria and they are not interchangeable: apixaban reduces on two of three (age 80 or above, weight 60 kg or below, creatinine 1.5 or above), while rivaroxaban and edoxaban reduce by creatinine clearance. Inappropriate dose reduction is as harmful as overdosing, because it leaves the patient unprotected while everyone believes they are anticoagulated.
Most Patients Do Not Need Bridging
BRIDGE showed no-bridging was non-inferior for thromboembolism with significantly less major bleeding in atrial fibrillation. Reserve bridging for high thrombotic risk: mechanical mitral valve, recent stroke or VTE within 3 months, and antiphospholipid syndrome. DOACs never need bridging given their short half-life; just stop them 24 to 48 h before.
Know the Reversal Agents
Warfarin: 4-factor PCC plus vitamin K, PCC over plasma for speed and volume. Dabigatran: idarucizumab. Apixaban and rivaroxaban: andexanet alfa, or PCC where unavailable. Heparin: protamine (only partially effective for LMWH). Reverse for life-threatening bleeding, not for an abnormal number.
Simplify Triple Therapy After PCI
In atrial fibrillation plus PCI, drop aspirin early, typically within a week, and continue an oral anticoagulant plus clopidogrel. Prolonged triple therapy bleeds far more than it prevents, and the trials consistently favored the shorter, dual regimen. Use a DOAC rather than warfarin where possible.
Pregnancy Is LMWH Territory
Warfarin is teratogenic and DOACs are contraindicated, since they cross the placenta and safety data are lacking. Use LMWH throughout, which does not cross the placenta, and plan the peripartum interruption in advance with obstetrics and anesthesia, since neuraxial anesthesia requires a defined interval since the last dose.
Think About Whether to Anticoagulate at All
Score the thrombotic risk with CHA2DS2-VASc and the bleeding risk with HAS-BLED, but use HAS-BLED to identify modifiable factors, not as a reason to withhold treatment. Set a duration and a review date, because indefinite anticoagulation started for a provoked event is one of the commoner sources of avoidable bleeding. Any heparin exposure with a falling platelet count means consider HIT, stop all heparin including flushes, and start a non-heparin agent.
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Anticoagulation
Choose, dose, reverse
Agent Selection
AF/VTE: DOAC first-line. Mechanical valve: warfarin only. APS (triple-positive): warfarin only. Cancer VTE: LMWH or DOAC. Acute inpatient: UFH (titratable) or LMWH.
Reversal Agents
Warfarin → 4F-PCC + vit K. Dabigatran → idarucizumab 5g IV. Xa inhibitors → andexanet alfa or 4F-PCC 50 U/kg. UFH → protamine. LMWH → protamine (partial).
Trials
BRIDGE 2015 · RE-LY · ROCKET AF · ARISTOTLE · TRAPS 2018 · RE-VERSE AD · ANNEXA-4 · HOKUSAI VTE Cancer
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