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Purpose: Assess the validity of ICD-9-CM and ICD-10 epilepsy coding from an emergency visit (ER) and a hospital discharge abstract database (DAD).
Methods: Two separate sources of patient records were reviewed and validated. (1) Charts of patients admitted to our seizure monitoring unit over 2 years (n = 127, ICD-10 coded records) were reviewed. Sensitivity (Sn), specificity (Sp), and positive and negative predictive values (PPV and NPV) were calculated. (2) Random sample of charts for patients seen in the ER or admitted to hospital under any services, and whose charts were coded with epilepsy or an epilepsy-like condition, were reviewed. Two time-periods were selected to allow validation of both ICD-9-CM (n = 486) and ICD-10 coded (n = 454) records. Only PPV and NPV were calculated for these records. All charts were reviewed by two physicians to confirm the presence/absence of epilepsy and compare to administrative coding.
Results: Sample 1: Sn, Sp, PPV, and NPV of ICD-10 epilepsy coding from the seizure monitoring unit (SMU) chart review were 99%, 70%, 85%, and 97% respectively. Sample 2: The PPV and NPV for ICD-9-CM coding from the ER database were, respectively, 99% and 97% and from the DAD were 98% and 99%. The PPV and NPV for ICD-10 coding from the ER database were, respectively, 100% and 90% and from the DAD were 98% and 99%. The epilepsy subtypes grand mal status and partial epilepsy with complex partial seizures both had PPVs >75% (ICD-9-CM and ICD-10 data).
Discussion: Administrative emergency and hospital discharge data have high epilepsy coding validity overall in our health region.
Epilepsy is one of the most commonly reported neurologic conditions in primary health care after migraine, and accounts for 1% of the global burden of disease (Murray et al., 1994). In Canada, 16,000 people are diagnosed with epilepsy every year, and at any given time approximately 200,000 people have active epilepsy requiring medical attention (Tellez-Zenteno et al., 2004). It is expected that the prevalence of epilepsy will increase with aging populations. It is thus necessary to develop cost-effective and timely surveillance programs using newly validated tools to monitor and project future social and clinical demands, and management and outcomes of epilepsy.
Current and past surveillance programs for epilepsy have relied primarily on random telephone, door-to-door, or mailed population-based surveys (Wiebe et al., 1999; CDC, 2005). Prospective epilepsy surveillance programs are extremely rare, primarily because of the high cost of active surveillance (Olafsson et al., 2005). In recent years, administrative data have become a highly sought after source of data for passive disease surveillance, assessment of health resource utilization, and the evaluation of healthcare outcomes (Wennberg & Gittelsohn, 1973; May et al., 1991; Virnig & McBean, 2001; Kokotailo & Hill, 2005; Jetté et al., 2008). The benefits of administrative databases include their large population sizes, their cost-effectiveness, and often their rich content of historical population-based information (Deyo et al., 1994; Mitchell et al., 1994; Iezzoni, 1997). This is particularly relevant in the Canadian context, in which centralized care and single-payer systems have resulted in population-based administrative databases at regional, provincial, and national levels.
Currently and since 2002, inpatient facilities across Canada use a slight modification of the World Health Organization (WHO) International Classification of Diseases (ICD) system, ICD-10-CA, to code inpatient visits (CIHI 2008). There are no significant differences in epilepsy codes between the ICD-10 and ICD-10-CA systems at the third or fourth digit/character level; therefore, the term ICD-10 is used for the remainder of the article. ICD-9-CM and ICD-9 are still the primary systems used for coding mortality and morbidity in many countries including Pakistan, India, and others (WHO, 2008). Although ICD-10 is used for mortality coding in the United States, ICD-9-CM is still in use for morbidity coding in the United States (WHO, 2008).
Validation of ICD-coded data from hospital and emergency room (ER) discharge abstract databases is one of the first steps in developing a valid and accurate case definition for a condition of interest for future surveillance. Some fatal conditions, such as cancer, are coded more accurately than nonspecific conditions due largely to pathologic confirmation of the diagnosis (Whittle et al., 1991; Tennis et al., 1993). One group in the United States validated epilepsy ICD-9-CM codes from administrative data (Holden et al., 2005a, 2005b). This group used data from a U.S. Managed Care Organization. They developed a computer algorithm to identify epilepsy cases in this database. The best model correctly identified 90% of cases.
The objectives of the present study were: (1) to validate epilepsy ICD-9-CM and ICD-10 coding from an inpatient and an emergency discharge abstract database; and (2) to compare variations in coding validity between the two ICD systems and between the various hospital settings in a large Canadian health region.