Factor VII Levels and International Normalized Ratios in the Early Phase of Warfarin Therapy

Abstract

Background Factor VII is the most affected clotting factor during the early phase of warfarin therapy. An international normalized ratio (INR) of more than 1.4 is considered unsafe for epidural catheter placement or removal, according to the American Society of Regional Anesthesia and Pain Medicine. The authors tested the hypothesis that factor VII activities would be consistent with safe removal of the epidural catheter on postoperative day (POD) 1 regardless of INR value. Methods Data from 121 patients who took warfarin after undergoing total joint surgery and had INRs and factor VII levels determined were reviewed. Patient characteristics and factor VII activities were compared between patients with INRs of more than 1.4 and those with INRs less than or equal to 1.4 on PODs 1, 2, and 3. Results Eleven patients had INRs of more than 1.4 on POD 1; their mean +/- SD factor VII activities were 60 +/- 28% (normal: 50-160%). On POD 2, 78 patients with INRs more than of 1.4 had factor VII activities of 32 +/- 15%, whereas on POD 3, 84 patients with INRs of more than 1.4 had factor VII activities of 44 +/- 19%. Variables included in the final multiple logistic regression model as predictors of an INR of more than 1.4 on POD 2 were warfarin dose on POD 1 and factor VII activity on POD 2. Conclusions The range of factor VII activities in the patients with INRs of more than 1.4 within 12 h of warfarin therapy was compatible with adequate hemostasis. The authors found no evidence that epidural catheters should not be removed even with INRs up to 1.9, the highest INR on POD 1 noted in their study.