When to Calculate CHA2DS2-VASc Score Relative to Warfarin Initiation
The CHA2DS2-VASc score should be calculated before initiating warfarin therapy to determine if anticoagulation is indicated, not on the day of or days after starting the medication—the score guides the decision to anticoagulate, not the monitoring of therapy once started. 1
Understanding the Purpose of CHA2DS2-VASc
The CHA2DS2-VASc score is a risk stratification tool used to assess stroke risk in patients with atrial fibrillation or atrial flutter, not a monitoring parameter for warfarin therapy. 1
The score determines whether anticoagulation is indicated in the first place, based on thromboembolic risk factors including congestive heart failure, hypertension, age ≥75 years (doubled), diabetes, prior stroke/TIA (doubled), vascular disease, age 65-74 years, and female sex. 1
The score should be calculated before making the decision to start anticoagulation, as it guides whether warfarin or other anticoagulants are appropriate for the patient. 1
What Should Be Monitored After Starting Warfarin
Once warfarin therapy is initiated, the relevant monitoring parameter is the INR (International Normalized Ratio), not the CHA2DS2-VASc score:
INR should be checked daily during warfarin initiation until the therapeutic range (2.0-3.0) has been reached and sustained for 2 consecutive days. 1, 2
After achieving therapeutic range, monitor INR 2-3 times weekly for 1-2 weeks, then reduce frequency based on stability of results. 1, 3
Once stable, INR testing can be reduced to intervals as long as 4 weeks. 1, 3
Timing of Warfarin Initiation with Heparin
When rapid anticoagulation is needed:
Warfarin should be started on the first or second day of heparin therapy, not delayed. 4, 2
Heparin must be continued for at least 4-5 days and until the INR has been in therapeutic range for 2 consecutive days, as the anticoagulant effect of warfarin is delayed. 3, 4, 2
The early INR elevation (within first 24-48 hours) reflects depletion of Factor VII and protein C, not full anticoagulation—full effect requires depletion of Factor II, which takes 4-5 days. 3, 4
Common Pitfall to Avoid
Do not confuse risk stratification scores (CHA2DS2-VASc) with therapeutic monitoring parameters (INR). The CHA2DS2-VASc score is calculated once to determine if anticoagulation is warranted; it does not change based on when warfarin is started and is not recalculated as part of warfarin monitoring. 1 The score may be reassessed periodically to reevaluate the ongoing need for anticoagulation, but this is independent of the timing of warfarin initiation. 1