Reliability of Group Health Cooperative automated pharmacy data by drug benefit status

Purpose: Evaluate the reliability of health plan pharmacy records in determining medication use among seniors with and without a drug benefit.

Methods: Subjects included 3610 seniors, enrolled in Group Health Cooperative's Medicare (GHC) + Choice program during 1998-1999, receiving care in an integrated group practice (IGP), and diagnosed with one or more of four chronic conditions (hypertension, diabetes, congestive heart failure, and coronary artery disease). We compared pharmacy records to self-reported medication use for antidepressant, antihypertensive, acid suppressant, cardiac, diabetic, hormone, and lipid lowering drugs.

Results: Agreement between pharmacy records and self-report was substantial to almost perfect (prevalence-adjusted and bias-adjusted kappa (PABAK) range: 0.69 for antihypertensives to 0.95 for cardiac agents) among seniors with a drug benefit. Agreement was slightly less for seniors without a drug benefit (PABAK range: 0.51 for antihypertensives to 0.92 for cardiac agents) and differences varied by drug class. Among seniors without a benefit, the prevalence of medication use was lower when based on pharmacy records than when based on self-report for all medication classes of interest.

Conclusions: While GHC may not be representative of all health plans, our study indicates that health plan pharmacy records are a reliable source of data for seniors receiving care within an IGP. However, the reliability of pharmacy records appears better among seniors with a drug benefit. Researchers should consider factors such as drug benefit status when conducting studies using pharmacy data. More studies are needed in different populations and delivery systems, as well as over varied types of drug benefits.