On Tuesday, August 1st, 2023 the University of Iowa Hospitals and Clinics (UIHC) will update the reference interval for the international normalized ratio (INR). This change will affect INR testing performed at the Core Laboratory and at Iowa River Landing, as well as point-of-care INR testing throughout UIHC and University of Iowa Community Clinic sites.

The current INR reference interval of < 4.0 was based on lower bleeding risk for patients taking warfarin. The updated INR reference interval of 0.8 – 1.2 is based on a healthy population. Patients taking warfarin will have an INR above this updated reference interval. A patient’s target INR range may depend on multiple factors, including the clinical indication for anticoagulation and bleeding risk. A standard intensity warfarin therapeutic INR range is 2.0 – 3.0.

Questions should be directed to Anna Merrill, PhD (678-8400, pager 7046, anna-merrill@uiowa.edu) or Matthew Krasowski, MD, PhD (pager 1171, matthew-krasowski@uiowa.edu).