Abstract 243: Impact of Dual Health Care System Use on Quality of Warfarin Anticoagulation in Atrial Fibrillation

Abstract

Background. Warfarin anticoagulation for atrial fibrillation (AF) requires routine INR blood testing, usually performed by a single anticoagulation clinic or provider. Regular INR testing improves INR control, and monthly INR testing and adequate time in INR therapeutic range are endorsed quality and performance measures. However, many Veterans with cardiovascular disease use VA and Medicare (MC) services concurrently. We therefore evaluated the association of outpatient dual health care system use with process measures of warfarin management. Methods. Using linked VA and MC inpatient, outpatient, drug prescription, and laboratory claims, we identified MC Part A/B eligible, non-MC Advantage, Veterans age ≥ 65 with prevalent atrial fibrillation or flutter who were prescribed warfarin from the VA (index date) between 1/1/2004 and 12/31/2008. The primary predictor was the degree of dual use for INR testing, expressed as the fraction of outpatient INRs obtained in the 12 months post-index date that occurred in Medicare (MC/[VA+MC]). The outcomes were 1) the INR monitoring rate (INRMR), expressed as the proportion of calendar months±6 days in which an INR was performed (consistent with AHA/ACC performance measures) and 2) VA-based time in INR therapeutic range of 2.0-3.0 (TTR). Results. We identified 394,854 patients (age 77.2 ± 6.1 years; 1.4% female) with AF and VA-issued warfarin meeting inclusion criteria. Of these, 43.3% used VA only for INR testing, 16.6% used MC only, and 39.1% used both VA and MC. Compared to patients who used VA only, dual health care system users were older and had higher CHADS2 and comorbidity index scores. Compared to patients with VA-only care, the proportion of patients with adequate achievement of performance measures (INRMR = 1.0 or TTR ≥ 60) varied by degree of dual use (p<0.001). Mean TTR was highest among patients with VA-only INR monitoring (Table, p < 0.001). Conclusion: More than half of Veterans age ≥ 65 with AF and VA-issued warfarin receive outpatient INR testing in MC. Dual health care system use is associated with lower achievement of process measures of quality of anticoagulation care, which could affect outcomes of stroke, hemorrhage and death.