Association of retest interval with inr control in warfarin patients with markedly out of range inrs

Document Type

Conference Proceeding

Publication Date


Publication Title

Research and Practice in Thrombosis and Haemostasis


Background : The ideal INR retest interval following warfarin dose changes for markedly out of range INRs is not clear. Guidelines from the International Society on Thrombosis and Haemostasis suggest retesting VTE patients with INRs ≥ 4.0 or ≤1.5 within 7 days based on a prior study showing higher time in therapeutic range in centers with shorter retest intervals. Aims : To determine if prompt retesting (≤7 days) results in better INR control across a broad cohort of patients at the patient-INR level. Methods : INRs ≥ 4.0 or ≤1.5 from the Michigan Anticoagulation Quality Improvement Initiative (MAQI 2 ) registry were identified. INRs from patients with target INR ranges of 2-3 were included, except those within 30 days of warfarin initiation or without a follow-up test. Based on the number of days between warfarin dose adjustment and the date of the next INR, INRs were categorized as promptly (≤7 days) or non-promptly retested. INR control was defined by whether or not the retest INR (1 st follow-up INR) or the 2 nd follow-up INR were in range. Comparisons were made using Chi square tests. A two-sided P < 0.05 was considered statistically significant. Results : A total of 36,822 eligible INRs were identified (22,399 ≤1.5; 14,423 ≥ 4.0). Prompt retesting occurred in 21,455 (58.3%). The median retest intervals were 5 days and 12 days for promptly and nonpromptly retested INRs, respectively. Prompt retesting was inferior for the retest INR being in-range (34.7% vs. 42.3%, P < 0.001) as well as the second follow-up INR being in range (42.8% vs 43.8%, P = 0.049). Conclusions : In this MAQI 2 cohort of patients, retesting markedly out of range INRs within 7 days appears to provide worse INR control over the short-term follow-up period. Further analysis of this data is needed to account for confounding patient factors that may affect INR control and prescribed retest intervals.

PubMed ID

Not assigned.