Percent Time in Range with Warfarin as a Performance Measure: How Long a Sampling Frame Is Needed?

Area of Science:

• Pharmacology
• Clinical Pharmacy
• Health Services Research

Background:

• Warfarin remains a critical anticoagulant for millions globally.
• Percent time in therapeutic range (TTR) is a key performance metric for warfarin therapy.
• Concerns exist that TTR measurement periods may not accurately reflect performance changes.

Purpose of the Study:

• To evaluate the impact of varying TTR measurement durations on performance assessment.
• To determine if shorter TTR calculation windows provide comparable site performance data.
• To identify an optimal TTR measurement period for clinical practice.

Main Methods:

• Analysis of data from 124 Department of Veterans Affairs sites over seven fiscal years (2008-2014).
• Comparison of TTR calculations using 2, 3, 4, and 6-month time segments.
• Evaluation metrics included patient retention, mean TTR, and site performance rankings.

Main Results:

• Shorter TTR windows (e.g., 2 months) selectively excluded patients with better anticoagulation control.
• Mean TTR was highest with longer periods (6 months: 65.2%) and lowest with shorter periods (2 months: 60.0%).
• 3-, 4-, and 6-month periods yielded similar results, including over 800 patients and mean TTRs between 64.9%-65.2%.

Conclusions:

• A 4-month TTR measurement period offers comparable results to a 6-month period for assessing site-level performance.
• The findings support using a 4-month period for future TTR-based performance evaluations.
• Adjusting the TTR measurement duration can improve the accuracy and responsiveness of performance monitoring.