Group Health Cooperative of Puget Sound

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Chapter: Pharmacovigilance: Overview of North American Databases

Group Health Cooperative of Puget Sound (GHC) is a health maintenance organization (HMO), established in 1947, which provides health care on a prepaid basis to approximately 562 000 persons in Washington State, located in the northwestern corner of the United States.


Group Health Cooperative of Puget Sound (GHC) is a health maintenance organization (HMO), established in 1947, which provides health care on a prepaid basis to approximately 562 000 persons in Washington State, located in the northwestern corner of the United States (Saunders Davis and Stergachis, 2005). Three-quarters of these enrollees receive all their care at Group Health facilities. A fifth of the total number of enrollees belong to a subsidiary of GHC, established in 1990, which provides a ‘point of service’ option that permits care from community providers other than Group Health providers. As the point of service cover-age is more expensive than that provided by Group Health providers, most of the coverage remains within the Group Health network. Although the majority of enrollees receive health benefits through their place of employment, coverage has been extended to 58 500 Medicare, 30 000 Medicaid and 18 000 Washington Basic Health Plan recipients, thereby expanding its membership to include elderly and low-income resi-dents (Saunders, Davis and Stergachis, 2005).

GHC offers comprehensive health care coverage for outpatient care, inpatient services, emergency care, mental health services, and prescribed drugs, although the latter are not provided to Medicare enrollees new to GHC since 1993. Nearly all benefit plans require small co-payments for services, such as prescrip-tions, outpatient visits unrelated to preventive care and emergency treatment. Coverage for outpatient drugs is controlled by GHC’s drug formulary.

At GHC, each enrollee is assigned a unique number, which remains with that person even if the individual drops out of the plan and then rejoins the health system at a later date. Multiple databases have been developed from the main database, with an individual’s records linked through their unique number.

The socio-demographic profile of GHC enrollees is generally comparable to that of the population of the Seattle–Tacoma area, with the GHC enrollees some-what better educated. The median income of both groups is similar, although the GHC membership is less representative of the highest income category.

Multiple database files exist, and date from vary-ing time-points. The current enrollment file consists of some 562 000 individuals; historical files contain records for some 2 million persons enrolled in GHC at any time since 1980 (Saunders, Davis and Ster-gachis, 2005). The Pharmacy file, dating from 1977, contains records generated when prescriptions are filled. Drug data include drug number, therapeutic class, drug form and strength, date dispensed, quan-tity dispensed, cost to GHC, and refill indicator. The file currently includes a field for number of days the medication should last. The hospital database, dating back to the early 1970s, includes diagnoses, proce-dures, diagnostic-related group (DRG) and discharge disposition. Laboratory data are available since 1986, and specify, in both inpatient and outpatient settings, the test ordered, the date ordered, specimen source, results and date of the results. All radiographic studies performed at GHC facilities, including MRI and CT scans, are now available in the outpatient visits file. Beginning in the early 1990s, diagnosis and procedure data were incorporated into the outpatient registra-tion database, which also includes date of visit, the provider seen, the provider’s specialty and the loca-tion of care.

As a longtime participant in the National Cancer Institute’s SEER (Cancer Surveillance, Epidemiology and End Results) program, GHC receives a data file of all newly diagnosed cancers among its enrollees, including anatomical site, stage of diagnosis and vital status at follow-up. This file covers a reporting area of 13 contiguous counties of northwest Washing-ton State, and is maintained by the Fred Hutchinson Cancer Research Center in Seattle, one of the 13 SEER population-based registries in the United States (see

GHC has developed a death file that covers enrollees from 1977. Data are also available from the Community Health Services department, from an immunization database (see section on Vaccine Safety Datalink (VSD) later in this chapter), and from claims databases for services purchased from non-GHC providers. Cost information is available through the Utilization Management/Cost Management Infor-mation System, developed in 1989.

Turnover in membership at GHC is estimated to be approximately 15% per year (Saunders, Davis and Stergachis, 2005). Since Group Health has been in existence for more than 50 years, a subset of enrollees can be identified whose tenure spans decades.

The GHC databases have been widely used for phar-macoepidemiologic research (Saunders, Davis and Stergachis, 2005), and GHC contributes to the HMO Research Network (see section below). Limitations to the GHC databases include its small size, a disad-vantage in the study of uncommon outcomes as most drugs are used by only a small percentage of the population; the lack of information on some important confounders, such as smoking and alcohol consump-tion; loss of drug coverage for its Medicare enrollees; and limitations of the GHC formulary, especially with regard to newly marketed drugs, since GHC may decide not to add a new drug or may delay its adop-tion until it has been on the market for a while. Drugs that offer little therapeutic or cost advantage over drugs already listed on the formulary may be excluded. Non-formulary drugs as well as over-the-counter drugs would be purchased for use outside the GHC pharmacy system, and therefore would not be represented in the database.

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