Performance of International Classification of Diseases, 9th Revision, Clinical Modification codes as an adverse drug event surveillance system

Background: Adverse drug events (ADEs) are one of the most frequent causes of iatrogenic injury. Because International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes are routinely assigned to inpatient discharges, they could provide a method to detect ADEs within a hospital, a state, and the nation. Objective: The objective of this study was to determine validity of selected ICD-9-CM codes in identifying inpatient ADEs. Research Design: An expert panel identified 416 ICD-9-CM codes to represent ADEs (flagged ADE codes). Retrospective chart review using a structured tool was performed to ascertain code performance in detecting ADEs. Subjects: Subjects included 3103 inpatients from all 41 acute care hospitals in Utah in 2001: 1961 inpatients sampled randomly (random sample) and 1142 inpatients sampled from the discharge records with at least one flagged ADE code (flagged sample). Measures: Measures were ADEs identified by structured review. Results: The flagged sample yielded 1 122 flagged ADE codes recorded in patient charts with 704 representing ADEs (63%). Two hundred eighty-six of the 704 verified ADE codes (41%) were determined to be inpatient ADEs. In the random sample, 32 of 58 ADEs (55%) causing hospital admission were detected by. the ADE-flagged codes. Only 23 of 224 inpatient ADEs had been assigned a flagged ADE code (10%). Conclusions: Flagged ADE codes have an overall positive predictive value of 63% and detect just over half of ADEs causing hospital admission. These codes have a positive predictive value of 25% for inpatient ADEs but detect only 10% of overall inpatient ADEs. Flagged ADE codes provide an imperfect but immediately available ADE surveillance system.