AUDIT OF THE FREQUENCY AND CLINICAL-RESPONSE TO EXCESSIVE ORAL ANTICOAGULATION IN AN OUTPATIENT POPULATION

A retrospective review of over-anticoagulated patients with critical i nternational normalized ratios (INRs) was undertaken in a large outpat ient laboratory. In the six-month study period, 85 prothrombin times ( PTs) were identified with an INR of greater than or equal to 6.0, an o verall incidence of elevated PTs of 0.2% or two per 1,000 INR tests. C omplete follow-up data was available on 65 patients. When compared to an age- and gender-matched control group without INR greater than or e qual to 6.0, high-INR patients were significantly more likely to manif est the presence of alcoholism or liver disease, to have been anticoag ulated for less than six months, to have experienced more frequent war farin dosage changes, and to have had the addition of a medication kno wn to interact with warfarin, In the high-INR group, a likely cause fo r the specific critical INR was identified in 44 patients (68%). Drug interactions followed by compliance problems were the most common fact ors identified. The 13 patients (20%) who received vitamin K therapy e xperienced no difference in the clinical outcome compared with those m anaged conservatively. Conservative management of critically high INR values appeared to be as efficacious as intervention with vitamin K th erapy. (C) 1998 Wiley-Liss, Inc.