Using ICD-9-CM Codes in Hospital Claims Data to Detect Adverse Events in Patient Safety Surveillance

Background: Adverse events (AEs) are significant and common sources of harm to inpatients. International Classification of Diseases, 9 Revision, Clinical Modification (ICD-9-CM) codes, assigned to virtually all inpatient discharges, could provide a readily available surveillance system capable of detecting a variety of AEs. Objectives: To determine the positive predictive value (PPV) of selected ICD-9-CM codes (flagged codes) in identifying inpatient AEs and AEs causing admission to the hospital. Methods: Samples were drawn from two distinct patient groups in calendar years 2001 and 2003: 7,070 inpatients from all acute care hospitals in Utah and 6,895 surgical inpatients from selected hospitals in Missouri. Structured chart review and abstraction identified all AEs and whether a flagged ICD-9-CM code represented an AE. AE codes were grouped into six categories to facilitate analysis: adverse drug events, surgical adverse events, misadventures, infections, device events, and other adverse events. Results: Among all inpatients, 4,416 of 11,619 flagged codes represented AEs (38 percent); 1,789 of the flagged codes were inpatient AEs (15 percent). Flagged code PPVs were higher for surgical inpatients, with 11,990 of 16,816 flagged codes representing AEs (74 percent), and 7,507 codes (46 percent) indicating inpatient AEs. There was wide variability among AE PPV categories, both for all inpatients (15 77 percent) and surgical inpatients (62 92 percent). Conclusions: Flagged AE codes were consistently more likely to indicate AEs in surgical inpatients than in all inpatient types. Given this, and the striking performance differences within and among AE code categories, ICD-9-CM codes are best suited to targeted AE surveillance.