Information gained from linking SEER cancer registry data to state-level hospital discharge abstracts

OBJECTIVES. Our goal was to link patients from the Iowa Surveillance, Epidemiology, and End Results (SEER) Registry to their respective inpatient discharge abstracts from an Iowa Health Care Cost and Utilization Project (HCUP)-formatted database and evaluate whether this linkage provides information related to cancer treatment variation. METHODS. Computer algorithms linked patients from the Iowa SEER Registry to discharge abstracts using 5 variables consistently defined between the databases (hospital identification, date of birth, admission date, discharge date, and zip code). Abstracts were reviewed for validity, and links not passing face validity were excluded., SUBJECTS. Our sample contained 7,296 patients with early-stage breast cancer (I, IIa, IIb) with surgery from the Iowa SEER Registry from 1989 through 1994 with contacts only with Iowa hospitals. RESULTS. Inpatient discharges abstracts were linked to 86.4% of the patients in our sample. More than 96% of the linked discharges for Medicare patients had a corresponding Medicare claim. Over 45% of the linked patients were not covered by Medicare. Comorbidity indexes were comparable to other published sources. Significant differences in diagnosis, comorbidities, and treatment were found across third-party payers. CONCLUSIONS. This linkage provides a valuable source of comorbidity and insurance data and perhaps the only source of secondary clinical information for the uninsured. This linkage is best suited for cancers requiring inpatient stays for treatment and for those states where border crossing for treatment is low.