Brief communicationAccuracy of ICD-9-CM codes in identifying infections of pneumonia and herpes simplex virus in administrative data
Introduction
Clinical epidemiology studies increasingly rely on electronic medical records data. The validity of International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis codes is crucial as they are often used to identify conditions of interest. Although many studies have used and validated ICD-9-CM codes for chronic conditions, such as rheumatoid arthritis or cancer, few studies have used ICD-9-CM codes to identify acute infectious conditions. Therefore, we evaluated the use of archived ICD-9-CM codes to identify two representative infection-related conditions, pneumonia and herpes simplex virus (HSV), in a defined health system. In addition, we explored strategies to improve the standard ICD-9-CM code-based selection.
Section snippets
Study design
Using 2000 to 2010 data within a defined cohort of Marshfield Clinic patients and Security Health Plan [1], we identified potential cases with ICD-9-CM diagnostic codes for pneumonia (480–486, N = 25,064) or HSV (054.0–054.9, N = 5661). We selected an evaluation sample of 175 subjects with a pneumonia code and 179 subjects with an HSV infection code for validation via medical chart review and adjudication. For each subject, trained research coordinators reviewed the electronic medical records
ICD-9-CM validation
Pneumonia ICD-9-CM codes confirmed medical record case status in 88% of patients, however, 10% were noncases and the evidence for 2% was equivocal. Similar results were observed for HSV, with 86% cases, 7% noncases, and 7% equivocal cases. The presence of a single ICD-9-CM code had a PPV of 88% for pneumonia and 86% for HSV. Demographic and clinical characteristics of the verified cases were compared with the noncases and equivocal cases (Table 1).
Verified pneumonia cases received multiple
Discussion
Our study demonstrates that ICD-9-CM codes for pneumonia and HSV were valid markers of a true history of these conditions. False positives (noncases) accounted for less than 10% of records evaluated for each condition. The PPVs for ICD-9-CM codes may differ across health care settings (e.g., inpatient), an important consideration when selecting cases. Furthermore, requiring a documented prescription, in addition to the infection-specific ICD-9-CM code, may improve correct identification of
Acknowledgments
The authors thank the study team at Marshfield Clinic Research Foundation for their work on this project: Nick Berger, Marilyn Bruger, Deanna Cole, Autumn Deedon, Deborah Hilgemann, Paul Hitz, Deb Johnson, Tara Johnson, Deb Kempf, Diane Kohnhorst, Cyndy Meyer, Aaron Miller, Suellyn Murray, DeAnn Polacek, Katie Pralle, Theresa Pritzl, Ashley Quinnell, Kristina Reisner, Sandy Strey, Rachelle Tuyls, and Daphne York.
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