Use of an electronic medical record for the identification of research subjects with diabetes mellitus

Abstract

Diabetes mellitus is a rapidly increasing and costly public health problem. Large studies are needed to understand the complex gene-environment interactions that lead to diabetes and its complications. The Marshfield Clinic Personalized Medicine Research Project (PMRP) represents one of the largest population-based DNA biobanks in the United States. As part of an effort to begin phenotyping common diseases within the PMRP, we now report on the construction of a diabetes case-finding algorithm using electronic medical record data from adult subjects aged > or =50 years living in one of the target PMRP ZIP codes. Based upon diabetic diagnostic codes alone, we observed a false positive case rate ranging from 3.0% (in subjects with the highest glycosylated hemoglobin values) to 44.4% (in subjects with the lowest glycosylated hemoglobin values). We therefore developed an improved case finding algorithm that utilizes diabetic diagnostic codes in combination with clinical laboratory data and medication history. This algorithm yielded an estimated prevalence of 24.2% for diabetes mellitus in adult subjects aged > or =50 years.

Figure 1.

Initial electronic classification of study subjects based upon two criteria: first, the presence or absence of diabetic diagnostic codes, and second, the presence or absence of relevant clinical laboratory data (e.g., glucose levels and glycosylated hemoglobin [HbA1c] levels). This strategy produced four data bins. These bins contain 1408, 14, 5597 and 1082 study subjects, respectively (total study population 8101). MESA = Marshfield Epidemiologic Study Area.

Figure 2.

Graphic representation of the clinical laboratory data from bin 3 (n = 5597), as classified in the text (potential false negative cases) and illustrated in figure 1 ▶. Glucose levels and glycosylated hemoglobin (HbA1c) levels were abstracted electronically for all 5597 subjects in bin 3. The 854 patients who had at least one glucose level and at least one HbA1c level are shown as circles in the scatter plot. The box plots in the margins reflect all available data. The mean is shown as a “+” within boxes representing the 25^th, 50^th and 75^th percentiles. Asterisks denote minimum and maximum. The dashed horizontal line indicates a glucose level 200 mg/dl.

Figure 3.

Proposed algorithm for identification of case subjects with diabetes mellitus (DM) in the Personalized Medicine Research Project (PMRP) database.