Positive predictive value of a case definition for diabetes mellitus using automated administrative health data in children and youth exposed to antipsychotic drugs or control medications: a Tennessee Medicaid study

Abstract

Background: We developed and validated an automated database case definition for diabetes in children and youth to facilitate pharmacoepidemiologic investigations of medications and the risk of diabetes.

Methods: The present study was part of an in-progress retrospective cohort study of antipsychotics and diabetes in Tennessee Medicaid enrollees aged 6-24 years. Diabetes was identified from diabetes-related medical care encounters: hospitalizations, outpatient visits, and filled prescriptions. The definition required either a primary inpatient diagnosis or at least two other encounters of different types, most commonly an outpatient diagnosis with a prescription. Type 1 diabetes was defined by insulin prescriptions with at most one oral hypoglycemic prescription; other cases were considered type 2 diabetes. The definition was validated for cohort members in the 15 county region geographically proximate to the investigators. Medical records were reviewed and adjudicated for cases that met the automated database definition as well as for a sample of persons with other diabetes-related medical care encounters.

Results: The study included 64 cases that met the automated database definition. Records were adjudicated for 46 (71.9%), of which 41 (89.1%) met clinical criteria for newly diagnosed diabetes. The positive predictive value for type 1 diabetes was 80.0%. For type 2 and unspecified diabetes combined, the positive predictive value was 83.9%. The estimated sensitivity of the definition, based on adjudication for a sample of 30 cases not meeting the automated database definition, was 64.8%.

Conclusion: These results suggest that the automated database case definition for diabetes may be useful for pharmacoepidemiologic studies of medications and diabetes.

Figure 1

Automated database case definition for diabetes mellitus. * Confirmation of initial diabetes related medical encounters were required when such encounters were identified from secondary inpatient ICD-9-CM diagnosis codes, outpatient ICD-9-CM diagnosis codes, or filled prescriptions for diabetes medications (see Table 1 for complete definitions for diabetes-related medical encounters and diabetes confirmation). Confirmation was needed in order to limit potential misclassification. Medical encounters identified from ICD-9-CM diagnosis codes were confirmed by a subsequent prescription for diabetes medications. Medical encounters identified form prescriptions were confirmed by subsequent ICD-9-CM diabetes diagnosis codes or by a subsequent diabetes medication prescription with a procedure indicating diabetes management.

Figure 2

Sample for validation of automated database case definition for diabetes mellitus. *Preliminary version of the cohort. ^†Counties (State of Tennessee) included: Cannon, Cheatham, Davidson, Dickson, Hickman, Lewis, Marshall, Maury, Montgomery, Robertson, Rutherford, Sumner, Trousdale, Williamson, Wilson. ^†Counties (State of Tennessee) included: Cannon, Cheatham, Davidson, Dickson, Hickman, Lewis, Marshall, Maury, Montgomery, Robertson, Rutherford, Sumner, Trousdale, Williamson, Wilson. ^‡There were 18 cases not adjudicated: 11--medical care provider identified, but patient record not located (most commonly for older records); 2--medical care provider not identified in Medicaid files; 2--medical care provider identified, but unable to visit (no longer practicing or relocated); 3--provider refusal. ^§There were 83 cases not adjudicated: 45--medical care provider identified, but patient record not located (most commonly for older records); 20--medical care provider not identified in Medicaid files; 11--medical care provider identified, but unable to visit (no longer practicing or relocated); 4--provider refusal 3--patient records identified but lacked sufficient information for case adjudication.