When to stop Low Molecular Weight Heparin (LMWH) in post-operative patients bridging with warfarin?

When to Stop LMWH on Post-Operative Bridging with Warfarin

Discontinue LMWH bridging when the INR reaches ≥2.0 for two consecutive days, typically 4-5 days after resuming warfarin. 1, 2

Timing of Warfarin Resumption

• Resume warfarin on the evening of surgery or the next morning at your patient's usual maintenance dose for those requiring long-term anticoagulation 2
• The FDA label specifies that warfarin and heparin (including LMWH) should overlap for 4-5 days until warfarin produces the desired therapeutic response as determined by PT/INR 3
• This overlap period accounts for warfarin's delayed onset of action, as its anticoagulant effect requires several days to reach therapeutic levels 4

INR Monitoring Schedule

• Check INR on postoperative day 4, then daily until therapeutic range is achieved 1, 2
• Discontinue LMWH when INR is >1.9 to 2.0 on two consecutive measurements 1, 4
• The target therapeutic INR range is typically 2.0-3.0 for most indications 2

Critical Timing Considerations for INR Testing

When drawing blood for INR while on concurrent LMWH and warfarin, timing matters significantly:

• Draw blood at least 10-12 hours after the last LMWH dose to avoid falsely elevated INR readings 5
• LMWH can artificially elevate point-of-care INR measurements by approximately 24% compared to laboratory values, potentially leading to premature discontinuation of LMWH before achieving true therapeutic anticoagulation 6
• Use standard reference laboratory methods rather than point-of-care devices for INR monitoring in patients on concurrent LMWH and warfarin to avoid dosing errors 6

Post-Operative LMWH Resumption Timing

The timing of when you restart LMWH post-operatively affects when you can ultimately stop it:

• For low-to-moderate bleed-risk procedures: Resume LMWH at least 24 hours after surgery 5, 1
• For high bleed-risk procedures (intracranial, spinal surgery, neuraxial anesthesia): Delay therapeutic LMWH for 48-72 hours 5, 2
• Consider prophylactic-dose LMWH initially for high-risk VTE patients during the 48-72 hour delay period before transitioning to therapeutic bridging doses 5

Common Pitfalls to Avoid

• Never discontinue LMWH based on a single INR measurement - require two consecutive therapeutic INRs to ensure stable anticoagulation 1, 4
• Avoid using point-of-care INR devices in patients on concurrent LMWH - these can overestimate INR by 25%, leading to 25% discordance in dosing decisions and premature LMWH discontinuation 6
• Do not stop LMWH prematurely in patients with mechanical heart valves, recent VTE (<3 months), or high thrombotic risk - these patients require confirmed therapeutic anticoagulation before stopping bridging 2, 7
• Administering therapeutic LMWH too soon after high bleeding-risk procedures increases major bleeding risk to 20% 2

Practical Algorithm

1. Resume warfarin at maintenance dose within 24 hours post-operatively 2
2. Resume LMWH 24 hours post-op (low-moderate bleed risk) or 48-72 hours (high bleed risk) 5, 2
3. Check INR starting on postoperative day 4 1
4. Continue daily INR monitoring until therapeutic 2
5. Stop LMWH when INR ≥2.0 on two consecutive days 1, 4
6. Ensure blood draws occur ≥10-12 hours after last LMWH dose 5
7. Use laboratory INR testing, not point-of-care devices 6