Use of ICD-10-CM coded hospitalisation and emergency department data for injury surveillance.

Injury surveillance, the ongoing, systematic collection, analysis, interpretation and dissemination of injury data, provides critical information to support public health efforts to reduce injuryrelated morbidity, mortality and disability. 2 For the past several decades, state and local health departments and national agencies in the USA have relied on the use of hospital discharge and emergency department (ED) data coded using the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9CM) to conduct injury surveillance. Surveillance case definitions and analyses have been based on ICD-9CM codes. However, a US mandate to code using the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10CM) 5 has resulted in a need to update injury surveillance case definitions and analysis guidance based on ICD-10CM. Beginning in October 2015, the US Department of Health and Human Services required all hospitals and healthcare providers covered by the Health Insurance Portability and Accountability Act to use the ICD-10CM to report electronic healthcare transactions. 5 The coding structure of ICD-10CM is based on ICD-10 mortality coding and classification published by the WHO, however, the classification scheme has been greatly expanded to capture the diagnostic detail needed for medical diagnoses. ICD-10CM contains nearly five times the number of codes found in ICD-9CM (approximately 72 000 codes in ICD-10CM compared with 15 000 codes in ICD-9CM). Because ICD-10CM captures greater detail than either ICD-9CM or ICD-10, this classification system has the potential to provide enhanced understanding of the types and causes of nonfatal injury. Epidemiologists and researchers who are transitioning from the use of ICD-9CM coded data to ICD-10CM coded data should note the substantial differences in the injury diagnosis and external causeofinjury codes in the two coding systems. These differences, which have the potential to either introduce or alleviate bias in nonfatal injury measurement, have been described in detail elsewhere. Important differences that have implications for injury surveillance include: ► Changes in the codes that identify events involving poisoning or toxic effects. In ICD-9CM, two codes were required to describe each poisoning event—a diagnosis code (960–979 and 980–989) to describe the type of drug or toxic substance involved and an external cause code (E850–E858, E860–E869, E930–E949, E950– E952, E961–E962 and E980–E982) to describe the intent of the poisoning or adverse effect (eg, accidental (unintentional), intentional selfharm, homicide or undetermined). In ICD-10CM, the information about both the drug or substance involved and the intent are captured in a single code (T36–T50 for drugs and biological substances, and T51–65 for toxic effects of nondrug substances). These T codes contain a character in the code to specify the intent of the poisoning (ie, accidental (unintentional), intentional selfharm, assault, undetermined, adverse effect and underdosing). ► Expansion of codes to identify events involving asphyxiation. ICD-10CM contains more than 40 diagnosis codes for asphyxiation or strangulation by different mechanisms (T71 codes), compared with a single diagnosis code in ICD-9CM (994.7). The T71 codes include a character in the code to specify the intent (ie, accidental (unintentional), intentional selfharm, assault and undetermined) of the asphyxiation. ► Separate codes in ICD-10CM (T74 and T76) distinguish between suspected and confirmed child and adult abuse and neglect. ► Introduction of the new concept of encounter type in ICD-10CM. Most injury diagnosis codes and external cause codes in ICD-10CM include a seventh character (a letter) that provides information on the type of medical care encounter when the diagnosis or external causeofinjury was determined. The character specifies whether the injury diagnosis is related to: (1) the initial encounter, defined as while the patient is receiving active treatment for the condition, (2) a subsequent encounter, defined as routine care during the healing or recovery phase after the active treatment phase has ended or (3) sequelae, defined as complications or conditions that arise as a direct result of an injury. ► Consideration of both diagnosis codes and external cause codes to identify all cases of intentional selfharm. In ICD-9CM, all mechanisms of intentional selfharm were captured using external cause codes. In ICD-10CM, while many mechanisms of intentional selfharm are captured using external cause codes (X71–X83), intentional selfharm involving poisoning or asphyxiation are captured by diagnosis codes (subsets of T36–T65 and T71). Collectively, the changes introduced with ICD-10CM mark a major change in the way that many types and causes of nonfatal injury are measured. For many injury subcategories, like drug overdose and asphyxiation, there is no simple onetoone crosswalk from ICD-9CM to ICD-10CM. As epidemiologists standardise new nonfatal injury surveillance methodologies using ICD-10CM, we cannot assume that injury trends will be consistent across the transition and we must strive to understand the predictive value, sensitivity and specificity of new injury codes and case definitions. With increased access to ICD-10CM coded hospital discharge and ED data, epidemiologists and researchers have begun to explore the nuances and implications of using ICD-10CM coded data for injury surveillance. To promote standardisation across time and among data sets, the US Centers for Disease Control and Prevention’s National Center for Injury Prevention and Control and National Center for Health Statistics have developed or updated basic case definitions and reporting frameworks for use with National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, Atlanta, Georgia, USA National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, Maryland, USA