ICD9 codes cannot reliably identify hemorrhagic transformation of ischemic stroke.

major objective of inpatient stroke care is the prevention of medical and neurological complications, although rare, hemorrhagic transformation (HT) of an isch-emic stroke (IS) can cause neurological deterioration and is associated with an increased risk of death. 1 If HT can be reliably identified in administrative data, it could become a component of hospital quality benchmarks. Previous studies have used administrative data to define HT of IS; however, the accuracy of International Classification of Diseases, Ninth Revision (ICD9) coding for this condition is unknown. 2–4 Coding algorithms used in previous studies have varied, but all have required a discharge diagnosis of IS, defined by ICD9 code or Clinical Classification Software code, and a discharge ICD9 for intracranial hemorrhage. We aimed to determine the accuracy of ICD9 coding for HT after IS using the Greater Cincinnati/Northern Kentucky Stroke Study (GCNKSS). Methods The purpose of the GCNKSS is to ascertain all strokes among a 5-county region that includes Cincinnati. Study personnel identified potential cases from January 1, 2005, through December 31, 2005, by screening emergency department encounters and inpatient admissions at 17 acute care hospitals for discharge ICD9 codes for stroke (430–436). Data are collected for all cases of IS, intracerebral hemorrhage (ICH), and subarachnoid hemorrhage. Potential cases were excluded if they had a discharge/autopsy diagnosis or neuroimaging with stroke but no clinical history consistent with stroke or if they had a clinical diagnosis of stroke and died within 24 hours of symptom onset without focal neurological deficit or confirmatory neuroimag-ing/autopsy. Detailed methods of the GCNKSS have been published previously. 5 For all potential cases, a research nurse abstracted history, physical examination, and diagnostic testing data, including neuroimag-ing. Study physicians reviewed the abstracted data and determined whether a stroke occurred, type of stroke, stroke mechanism, and whether HT was present. HT was characterized as asymptomatic or symptomatic (any neurological deterioration). For each HT case, hospital discharge ICD9 codes were examined. Our primary expectation was that HT cases would have an ICD9 code for both IS (433.x1, 434.x1, 436) and ICH (431). We looked separately at cases that were treated with recombinant tissue plasminogen activator and evaluated the combination of ICD9 codes for IS with any ICD9 code for intracranial hemorrhage (430, 431, 432). Results The GCNKSS identified 2159 cases of IS through hospital discharge screening, of which 102 had HT (symptomatic or asymptomatic). Among HT cases, 26 (25%) had an ICH code …