Prospective assessment of a nomogram for the initiation of oral anticoagulation therapy for outpatient treatment of venous thromboembolism.

Venous thromboembolism is a common medical problem. Recently, the emphasis has been on a switch to outpatient low molecular weight heparin therapy. Previous warfarin nomograms have been developed only for inpatients. We prospectively assessed a warfarin initiation nomogram in 105 consecutive outpatients; the nomogram requires International Normalized Ratio (INR) testing on only days 3, 5, and 8. Eighty-three percent had a therapeutic INR by day 5 and 98% by day 8. There were no major bleeds and only 6 instances of INR >4.5. This outpatient warfarin nomogram appears to be safe and efficacious in obtaining timely therapeutic levels of warfarin and deserves further study.