Conducting a matched-pairs historical cohort study with a computer-based ambulatory medical record system.

We describe techniques for using the Computer-Stored Ambulatory Record (COSTAR) at the Massachusetts General Hospital to conduct a historical cohort study of the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on blood pressure control. A query language was used to identify patients satisfying clinical and data-availability criteria, to match these patients with clinically similar patients not exposed to NSAIDs, and to collect data from the COSTAR records of both groups of patients to determine any differences in outcome. We analyzed over 30,000 patient records to select 90 pairs of patients used in the study. This approach to clinical research uses data collected for purpose of patient care and so does not require the separate recording of patient data for clinical research. Using computer-based medical record systems with a query language allows selection and matching of patients using detailed demographic and clinical criteria. The ability to conduct such studies is an advantage of computer-based medical record systems over the paper record system.