Diagnostic E-codes for commonly used, narrow therapeutic index medications poorly predict adverse drug events
Meyers Primary Care Institute; Department of Medicine, Division of Geriatric Medicine
Medical Subject Headings
Adverse Drug Reaction Reporting Systems; Aged; Anti-Arrhythmia Agents; Anticoagulants; Anticonvulsants; Cross-Sectional Studies; Digoxin; Forms and Records Control; Hospitalization; Humans; International Classification of Diseases; Medical Records; Patient Discharge; Pennsylvania; Pharmaceutical Preparations; Phenytoin; Warfarin
Health Services Research | Primary Care
OBJECTIVE: We sought to examine the validity of specific hospital discharge codes in identifying drug toxicity precipitating hospitalization, among elderly users of high-risk medications.
STUDY DESIGN AND SETTING: We conducted a cross-sectional evaluation assessing the diagnostic test characteristics of International Classification of Diseases-9 External-Cause-of-Injury codes (E-codes) compared with a reference standard of medical record review. This study was nested within a prospective cohort of elders using warfarin, digoxin, or phenytoin as identified in the Pharmaceutical Assistance Contract for the Elderly benefit program.
RESULTS: We identified 4,803 subjects contributing 11,409 person-years of exposure to at least one of three drug groups. Subjects experienced 8,756 hospitalizations, of which 304 were deemed, by expert review, to be a result of an adverse event of warfarin, digoxin, or phenytoin. The sensitivity, specificity, and positive (PPVs) and negative predictive values for drug-specific E-codes were warfarin--25.5%, 98.3%, 46.6%, and 95.7%; digoxin--84.0%, 99.1%, 56.8%, and 99.8%; and phenytoin--86.7%, 98.7%, 59.1%, and 99.7%.
CONCLUSIONS: E-codes for digoxin and phenytoin have a high sensitivity, but E-codes for all three medications have poor PPVs, a result that might produce misclassification in studies based solely on discharge coding. Investigators should confirm such rare events via medical record review.
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Citation: J Clin Epidemiol. 2008 Jun;61(6):561-71. Epub 2008 Feb 14. Link to article on publisher's site