What is the recommended Prothrombin Time/International Normalized Ratio (PT/INR) criteria before surgery for patients on anticoagulation therapy?

Preoperative PT/INR Criteria for Surgery

For most major surgeries, warfarin should be stopped 5 days preoperatively to achieve an INR ≤1.5 at the time of the procedure, while minor procedures with easily controlled bleeding (dental extractions, cataract surgery, minor dermatologic procedures) can proceed safely with continued warfarin and an INR of 1.5-1.8. 1

Major Surgery INR Targets

The target INR for major surgery is ≤1.5 to minimize bleeding risk while allowing safe surgical intervention. 1, 2

• Stop warfarin 5 days (approximately 120 hours) before surgery to allow adequate decay of anticoagulant effect 1
• Warfarin's half-life of 36-42 hours requires at least 5 days for most anticoagulant effect elimination, though elderly patients may experience delayed decay 1
• Prospective data demonstrates that only 7% of patients have INR >1.5 when warfarin is stopped 5 days preoperatively 1
• For patients at low thrombotic risk (bileaflet mechanical aortic valve without risk factors), warfarin can be stopped 48-72 hours preoperatively to achieve INR <1.5 without bridging 1

Minor Procedures INR Targets

For minor procedures where bleeding is easily controlled, target INR of 1.5-1.8 is acceptable, or warfarin can be continued without interruption. 1

• Minor dental procedures, skin procedures, and cataract surgery can proceed with continued warfarin therapy 1
• A shorter warfarin interruption interval (2-3 days) may suffice for minor procedures to achieve INR 1.5-1.8 1
• Continuing warfarin around the time of minor procedures does not significantly increase major hemorrhage risk when local hemostatic measures are available 1

Bridging Anticoagulation Considerations

High-risk patients require bridging with therapeutic heparin when INR falls below 2.0, while low-risk patients can safely forgo bridging. 1, 2, 3

High-Risk Patients Requiring Bridging:

• Any mechanical mitral valve replacement 1
• Mechanical aortic valve with risk factors (atrial fibrillation, prior thromboembolism, hypercoagulable state, older generation valve) 1
• Recent venous thromboembolism (<3 months) 2
• CHADS₂ score ≥5 in atrial fibrillation 2

Bridging Protocol:

• Start therapeutic LMWH or IV unfractionated heparin when INR falls below 2.0 (typically 48 hours after stopping warfarin) 1, 2, 3
• Last preoperative LMWH dose should be 24 hours before surgery, not 12 hours, as 34% of patients have therapeutic anticoagulant levels at surgery when dosed 12 hours preoperatively 3
• Stop IV unfractionated heparin 4-6 hours before surgery 1, 3

Invasive Cardiac Procedures Specific Targets

For percutaneous coronary intervention via radial approach, target INR ≤2.0; for femoral approach, target INR ≤1.5. 1

• Elective procedures should ideally have a brief wash-out period from anticoagulant effect 1
• For urgent/emergency procedures where warfarin cannot be stopped, radial access is strongly preferred 1
• Bridging with parenteral anticoagulation should be considered for acute coronary syndrome presentations but can be forgone in stable coronary disease 1

Postoperative Resumption

Resume warfarin at the usual maintenance dose on the evening of surgery or next morning, with bridging continued until INR ≥2.0 for 2 consecutive days. 2, 4

• For high bleeding risk procedures (intracranial, spinal surgery), delay therapeutic anticoagulation for 48-72 hours 2, 3
• For low-to-moderate bleeding risk, resume LMWH at least 24 hours postoperatively 2, 3
• Check INR daily until stable therapeutic range achieved 4
• Draw INR at least 10-12 hours after last LMWH dose to avoid falsely elevated readings 2

Critical Pitfalls to Avoid

Never give high-dose vitamin K routinely for preoperative warfarin reversal, as this creates a hypercoagulable state and makes re-anticoagulation difficult. 1

• Stopping warfarin only 2-3 days preoperatively results in mean INR of 1.8 at surgery—insufficient for most major procedures 1
• Administering therapeutic LMWH too soon after high bleeding risk procedures increases major bleeding to 20% 2
• Fresh frozen plasma is preferred over vitamin K for emergency surgery requiring immediate reversal 1
• Elderly patients may require longer warfarin interruption periods due to delayed anticoagulant decay 1