What is the normal Prothrombin Time (PT)/International Normalized Ratio (INR) for a patient undergoing surgery?

Normal PT/INR for Surgery

For most surgical procedures, the target preoperative INR should be <1.5, with an ideal threshold of <1.4 to minimize bleeding risk while allowing safe surgery. 1, 2, 3

Standard Preoperative INR Targets

**The American College of Chest Physicians recommends stopping warfarin 5 days before surgery to allow the INR to normalize to <1.5 at the time of the procedure.** 1, 2 This 5-day interruption period is sufficient for most patients, with prospective data showing only 7% of patients have an INR >1.5 on the day of surgery when this protocol is followed. 2

Evidence-Based Thresholds

• An INR <1.5 is the standard target for major surgical procedures according to multiple guidelines, balancing bleeding risk against procedural safety. 1, 2
• Large retrospective data from 636,231 surgical patients demonstrates that even INR values between 1.0-1.49 carry increased bleeding risk (adjusted OR 1.22 for major bleeding) compared to INR <1.0. 3
• The optimal preoperative INR threshold to predict increased bleeding risk is actually 1.10, with mortality risk increasing at INR ≥1.13. 3
• For hip fracture surgery specifically, INR <1.6 is considered safe, as values ≥1.6 are independently associated with increased mortality and values ≥1.8 with increased transfusion requirements. 4

Risk-Stratified Approach by Procedure Type

Low-Risk Procedures

Minor procedures such as dental extractions or dermatologic surgery can safely proceed with INR up to 2.5-3.0 without warfarin interruption. 2, 5 This avoids unnecessary thrombotic risk in patients who can tolerate therapeutic anticoagulation during minimal bleeding risk procedures. 1

High-Risk Procedures

For neuraxial blockade, major surgery, or procedures with high bleeding risk, target INR <1.5 is mandatory. 1 The European Society of Cardiology specifically recommends checking INR on the day before or day of surgery for these cases. 2

Management of Elevated Preoperative INR

If INR Remains >1.5 One to Two Days Before Surgery

Do not routinely administer vitamin K; instead, postpone the procedure to allow natural INR normalization. 1, 2, 5 The American College of Chest Physicians explicitly recommends against routine preoperative vitamin K for INR >1.5 measured 1-2 days before surgery. 5

For Minimally Elevated INR (1.5-1.9)

• For procedures that can tolerate slightly elevated INR, consider proceeding with INR 1.5-1.9 if the bleeding risk is low and accessible hemostasis is possible. 6
• If vitamin K is necessary, use low-dose oral vitamin K (1-2.5 mg) to lower INR to ≤1.5, which typically normalizes INR within 24 hours. 5
• Avoid high-dose vitamin K (>5 mg) as this creates difficulty achieving therapeutic INR postoperatively and may induce a hypercoagulable state. 2

Special Populations Requiring Caution

Mechanical Heart Valve Patients

Exercise extreme caution with vitamin K administration in mechanical valve patients to avoid valve thrombosis. 1, 2, 5 Never allow INR to fall rapidly in these patients. 1 High-risk patients (mechanical mitral valve, recent thromboembolism within 3 months, or mechanical valve with additional risk factors) require bridging anticoagulation with therapeutic-dose LMWH or unfractionated heparin during warfarin interruption. 1, 2

Patients on Bridging Anticoagulation

• Stop therapeutic-dose IV unfractionated heparin 4-6 hours before surgery. 1
• Administer the last preoperative dose of therapeutic LMWH 24 hours before surgery rather than 12 hours before to minimize bleeding risk. 1
• When drawing blood for PT/INR determination in patients receiving both heparin and warfarin, wait at least 5 hours after the last IV bolus heparin dose, 4 hours after cessation of continuous IV heparin infusion, or 24 hours after the last subcutaneous heparin injection. 6

Emergency Surgery Considerations

For emergency surgery with elevated INR, administer prothrombin complex concentrate (PCC) 50 IU/kg for immediate reversal. 1 Add low-dose intravenous vitamin K (1-2.5 mg or up to 10 mg for severe bleeding) for sustained effect, as plasma products have shorter half-life than warfarin. 1, 2 Fresh frozen plasma is an alternative if PCC is not available, but should not be used as elective prophylaxis. 1

Critical Pitfalls to Avoid

• INR is a poor predictor of bleeding risk in patients not on vitamin K antagonists, including those with cirrhosis, disseminated intravascular coagulation, massive transfusion, or acute trauma. 1 Do not use INR to guide plasma transfusion in these populations. 1
• Prophylactic plasma transfusion does not reduce bleeding in nonbleeding patients with incidentally abnormal INRs and lacks biological plausibility, as plasma infusion does not meaningfully change INR values below 1.5-2.0. 1
• Avoid routine bridging anticoagulation in atrial fibrillation patients, as the thrombotic risk during brief warfarin interruption is low and bridging increases bleeding risk. 1
• Do not use point-of-care INR testing for high INR ranges (>3.0), as significant discrepancy occurs compared to conventional laboratory testing, with laboratory INR being more reliable. 7