Psychometric Properties of an Instrument Measuring Patient's Knowledge about Coumadin

More than 2 million adults are self-managing Oral Anticoagulation Therapy (OAT) which require that patient be actively involved in maintaining the balance between clotting and bleeding. Yet, few instruments are available to measure OAT knowledge. The objectives of this study were to: 1) determine the psychometric properties of the Knowledge Information Profile about Coumadin (KIP-C), 2) measure the literacy levels of patients receiving Coumadin in the urban clinic and, 3) determine how literacy, sociodemographic, and health characteristics relate to knowledge about Coumadin. An exploratory factor analysis of the tetrachoric correlation matrix was performed. A sample of 192 patients participated in the study. Patients taking Coumadin for an average of 4.8 years demonstrated a surprising gap in fundamental health literacy knowledge essential to the safe self management of oral anticoagulation therapy. In terms of the KIP-C, the final model with three factors, 14 items, and one error covariance, had a good fit to the data (chi-square = 90.93, df = 74, p = .09, comparative fit index = .94, and root mean square error of approximation = .035) and all factor loadings were significant (p < .05) using the critical ratio/Wald test. The test-retest correlation for the total scale was .68. Each of the factors was sufficiently distinct that subscale scores were also deemed appropriate. The subscale alpha reliabilities were .65, .60, and .58, for the factors: Foods, Beverages & Medicine; Side Effects; and Vitamin K Knowledge, respectively. More testing is needed to develop a reliable tool for assessing Coumadin knowledge.