Billing diagnoses do not accurately identify out of hospital cardiac arrest patients: An analysis of a regional healthcare system.
BACKGROUND International Classification of Diseases 9th Edition's Clinical Modification (ICD 9CM) codes are frequently used in health services research. We tested the operating characteristics of ICD 9CM codes for identifying out of hospital cardiac arrest (OHCA) subjects. METHODS We used ICD 9CM codes to generate an "administrative cohort" of subjects treated after possible OHCA at one of six emergency departments (EDs) between January 2010 and April 2014. We performed a structured chart review to determine proportion of this administrative cohort with actual OHCA (true positive rate for the ICD 9CM based search method) The largest study site maintains a prospective registry of consecutive OHCA subjects, which we used to construct a "registry cohort" We used this cohort to calculate the sensitivity of the ICD 9CM based search strategy at this site, and compared in hospital mortality and discharge dispositions between the two cohorts using Chi square tests. RESULTS ICD 9CM codes identified 2461 subjects that comprised the administrative cohort. Of these, the true positive rate for actual OHCA on chart review was 40% ICD9 CM code sensitivity was 100% for subjects coded as dead on arrival and 19% for subjects coded as surviving to ED disposition. There were 609 OHCA subjects in the registry cohort and 268 subjects in the administrative cohort who presented to registry site. Only 26 subjects appeared in both cohorts. In hospital mortality was significantly higher in the administrative cohort than the registry cohort (91% vs. 61% p<0.001) and hospital discharge disposition of survivors was less favorable (p<0.001) Neither difference persisted after excluding subjects surviving <6h. CONCLUSION Compared to a prospective registry, ICD 9CM codes are an insensitive method to identify OHCA subjects. Moreover, ICD 9CM codes identify a biased sample of the OHCA population with higher mortality.
Resuscitation