Minor oral surgery and interference with anticoagulation in patients taking warfarin: a retrospective study.

Fundamental to the surgical treatment of patients taking warfarin is the monitoring of the international normalised ratio (INR) before and after operation. A postoperative rise in INR was observed to be more common than a postoperative fall, so we decided to test the null hypothesis that there is no difference in the INR before and after minor dentoalveolar surgery. Data from the dental records of 71 patients treated consecutively over an 18-month period were examined, and INR before and after operation tested by a Friedman non-parametric test (ANOVA). Six cases were removed from the study because they required perioperative adjustment of their warfarin. There was a significant increase in the postoperative INR for the whole group. Further analysis showed that a significant increase in the postoperative INR for the multiple extraction and surgical removal group was the most likely cause for the rise in the whole group. There was no significant increase between men and women, those taking antibiotics preoperatively, and those not doing so, or in those having a single tooth extracted. We found an association between the degree of surgical intervention and the likelihood of anticoagulation being affected. Postoperative INR in this group should be monitored carefully.