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Background: Oral anticoagulation therapy using Coumadin (warfarin) requires significant patient involvement. Limited validated instruments exist to test patient knowledge of Coumadin, and low health literacy may impede patient self-management. Objective: This article reports the psychometric testing of the Knowledge Information Profile-Coumadin (KIP-C20) to determine ( a ) minimum number of items and dimensions, ( b ) reliability, and ( c ) construct validity. Methods: Participants (N = 192) were recruited from outpatient pharmacist-directed anticoagulation clinics associated with an urban teaching hospital in the Midwest United States. Instruments were the Animal Naming test (AN), Rapid Estimate of Adult Literacy in Medicine (REALM), and KIP-C20. Multidimensional item response theory modeling and exploratory factor analyses were used to determine the best fitting model. Results: The final instrument, renamed KIP-C14, with 3 factors and 14 items, had a good fit to data (M 2 = 96.49, P < .0001; root mean square error of approximation = .04), and all factor loadings were .3 or larger. Internal consistency reliability was .65; test-retest correlation was .67. The KIP-C14 correlated positively, as expected, with years of Coumadin treatment. Subscales were differentially correlated with sociodemographic variables. Conclusions: The KIP-C14 had nearly identical, slightly higher reliability than the KIP-C20. Still, reliability was lower than expected, indicating a promising clinical assessment scale in need of further refinement., Competing Interests: Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2014.)