Estimating the Impact of Oral Diabetes Medication Adherence on Medical Costs in VA.
BACKGROUND
. Despite evidence demonstrating clinical benefits of oral hypoglycemic agents (OHAs), adherence to OHAs is generally poor. The economic benefit of OHA adherence among patients in the Veterans Affairs Health System (VA) is unknown.


OBJECTIVE
. This study assessed the impact of OHA adherence on medical costs and hospitalization probability in a VA population.


METHODS
. This retrospective cohort study included 26 051 VA patients with diabetes who completed the 2006 Survey of Health Care Experiences of Patients. We calculated total costs in fiscal year (FY) 2007 from the VA perspective as the sum of costs for all inpatient and outpatient services provided by VA. We measured adherence using the medication possession ratio (MPR), which reflected the proportion of days covered in FY2007. Patients were classified as adherent if MPR ≥80%. Analyses using instrumental variables (IVs) addressed potential biases from unobserved confounding.


RESULTS
. On average, adherent patients incurred lower total medical costs ($4051 vs $5133, P < 0.001) and were less likely to be hospitalized (4.6% vs 7.2%, P < 0.001) compared with nonadherent patients. After covariate adjustment, adherence was associated with a $170 reduction in total costs (P < 0.011) and a 1.5 percentage point decrease (P < 0.001) in hospitalization probability. IV estimates indicated that the impacts of OHA adherence were larger in magnitude.


CONCLUSIONS
. On average, OHA adherence was associated with lower medical costs of at least $170 per patient over a 1-year period. Results from this study are important for informing policy decisions to broadly disseminate programs to promote diabetes medication adherence, particularly in a VA setting.
VA Puget Sound Health Care System, Seattle, WA, USA University of Washington, Seattle, WA, USA edwin.wong@va.gov.
Edwin S
ES
Wong
VA Puget Sound Health Care System, Seattle, WA, USA University of Washington, Seattle, WA, USA.
Chris L
CL
Bryson
VA Puget Sound Health Care System, Seattle, WA, USA University of Washington, Seattle, WA, USA.
Paul L
PL
Hebert
VA Puget Sound Health Care System, Seattle, WA, USA University of Washington, Seattle, WA, USA.
Chuan-Fen
CF
Liu
Department of Veterans Affairs; diabetes; instrumental variables; medical costs; medication adherence