Assessing the Ability of Warfarin Treated Patients to Predict Their INR

ASSESSING THE ABILITY OF WARFARIN TREATED PATIENTS TO PREDICT THEIR INR Kathleen McNamara, James Hoehns, Matthew Witry

The international normalized ratio (INR) is the accepted lab test used to measure the intensity of warfarin effect. The conventional wisdom is that patients receiving warfarin are unable to correctly determine, in the absence of an INR result, whether or not they are therapeutic at any given time. Some warfarin treated patients express that they have insight into what their INR result will be. Various patient related factors may contribute to these opinions.

Our objective is to assess how accurately patients can guess their INR result before it is obtained and to describe factors which inform their opinion of what their INR will be. In this prospective study, the investigators will enroll warfarin treated patients from 7 anticoagulation clinics in Iowa. Inclusion criteria are: age ≥18 years, warfarin use ≥60 days, INR goal of 2.0-3.0 or 2.5-3.5, expected warfarin use >6 months, and English speaking. Exclusion criteria include: use of self INR-testing, home INR draws, dementia, or residing in a long-term care facility. A data collection form will be completed prior to INR measurement for a 6 month period. Information will be collected for subject demographics, warfarin adherence, INR stability, INR prediction, and prediction rationale.

INR monitoring represents a significant burden with respect to cost and time. The results of this study may identify patient factors which could help individualize and decrease the frequency of INR monitoring in patients who receive maintenance warfarin therapy.

Inclusion criteria

• Age ≥18 years
• Warfarin use ≥60 days
• INR goal of 2.0-3.0 or 2.5-3.5
• Expected warfarin use >6 months
• English speaking

Exclusion criteria

• Self INR-testing
• Home INR draws
• Dementia
• Residence of a long-term care facility