Warfarin maintenance dosing algorithms improve the time in therapeutic International Normalized Ratio (INR) range (TTR), a surrogate marker for clinical outcomes. Despite demonstrated benefits, it has been reported that just over a fourth of anticoagulation providers utilize experience-based dosing instead. This study assessed rates of concordance between experience-based and algorithm-based warfarin dosing at a single anticoagulation clinic.
Within the University of Utah Health’s Thrombosis Service, patients in the maintenance phase of their warfarin therapy with an INR goal of 2.0-3.0 or 2.5-3.5 and who had INR results during November 2019 were included. Experienced-based approaches for out-of-range INRs were compared to a validated dosing algorithm to determine algorithm concordance rates as well as the likelihood that algorithm concordance would return the INR into therapeutic range.
During the one-month study period, there were 1120 (43.7%) out-of-range INRs in 770 patients included in this analysis. Providers’ decisions were 50.5% algorithm-concordant for dosing adjustments and 59.2% concordant for follow-up intervals. Algorithm-concordant dosing practices resulted in a significantly higher likelihood of returning the subsequent INR to the target range (odds ratio [OR] 1.325, 95% confidence interval [CI] 1.047-1.676), whereas algorithm-concordant follow-up intervals did not significantly impact return of INR to therapeutic range (OR 0.788, 95% CI 0.621-1.001). No provider characteristics significantly impacted the rate of return to INR goal.
This single-center study demonstrated that experience-based dosing was 50% concordant with a validated algorithm and that algorithm-concordant dosing increased the likelihood of returning the INR to therapeutic range. These findings support strategies that either align experience-based dosing better with algorithm-based principles or strengthen the recommendation for using a validated dosing algorithm.
- Unintentional algorithm concordance occurred approximately 50% and 60% of the time for dosing and follow-up times, respectively.
- Algorithm concordant dosing resulted in increased rates of return to therapeutic INR at subsequent INR tests.
- Follow-up time intervals did not contribute towards a significant difference in the rates of return to INR goal between algorithm concordant and discordant practices.
- Few provider demographic groups demonstrated increased unintentional algorithm concordance, though no groups demonstrated increased rates of return to INR goal at subsequent INR tests.
- Additional research of algorithm use for specific patient demographics or anticoagulation indication may prove to be beneficial in illustrating specific incidences when following warfarin dosing algorithms are optimal.
Keywords: warfarin, maintenance dosing, INR, TTR, algorithm, anticoagulation clinic
Abbreviations: Time in Therapeutic Range (TTR), International Normalized Ratio (INR)Recommend0 recommendationsPublished in