Health Services Research & Development

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2006 HSR&D National Meeting Abstract


1053 — Impact of a Medication Co-Payment Increase on Blood Pressure Among Veterans

Author List:
Doshi JA (CHERP)
Lee BY (Univ of Pittsburgh)
Volpp KG (CHERP)

Objectives:
Numerous studies suggest that small prescription copayment increases significantly reduce medication use, particularly within low income populations. However, little research has examined how copayment increases impact health outcomes. In February 2002, the VA increased prescription co-payments from $2 to $7 for many veterans. We examined the impact of this change on blood pressure (BP) among Philadelphia VA patients of different income levels.

Methods:
We examined BP during the 24-months pre and post copayment increase using VA medical records. Our cohort included veterans who used antihypertensive medications in the pre-period and had BP readings in the pre- and post-periods (n=5,364). Veterans who remained copay exempt were a natural control group. However, given substantial differences in baseline characteristics and health trajectories of the two groups, we used a difference in difference (DD) approach to compare changes in BP across patients of different income levels among veterans subject to the copayments. Patient household income was derived from zip-code matched census data. Regression models examined changes in the mean systolic BP (SBP) and likelihood of SBP > 140 mm Hg following copayment increase across income quartiles (<= $36,883, $36,884-$49,289, $49,290-$58,843, and >=58,884). Subgroup analyses were conducted among patients with and without CAD or diabetes.

Results:
Patients in the lowest income quartile had, on average, a 2.58 mm Hg increase in mean SBP between the pre- and post-periods compared to decreases of 0.4 in the second quartile, 1.35 in the third quartile, and 1.5 in the highest income quartile. The proportion of patients with mean SBP>140 mm Hg increased by 8.1% in the lowest income quartile relative to 2.8 to 3.5% in the three upper quartiles. Regression results confirmed significant differences in BP outcomes between the lowest and highest income quartile. Similar results were observed in both higher-risk patients with and without a history of CAD or diabetes.

Implications:
Our results indicate that increases in medication co-payments may have negatively impacted BP control in lower income veterans, including those at high cardiovascular risk.

Impacts:
While implemented for budgetary reasons, VA co-payment increases may worsen disparities in cardiovascular outcomes between high and low income veterans.