ElixhauserIndex

The Elixhauser index, also known as the Elixhauser comorbidity index, is a set of 30 diagnostic categories designed to summarize a patient’s comorbidity burden using administrative hospital data. Developed by Anne Elixhauser and colleagues and first published in 1998, the index is intended for risk adjustment in observational studies and health services research. The 30 conditions cover a broad range of chronic and acute illnesses across cardiovascular, pulmonary, renal, hepatic, metabolic, neurologic, infectious, oncologic, and psychiatric domains. Each condition is defined by a set of ICD-9-CM discharge codes and, with the adoption of ICD-10-CM, corresponding ICD-10-CM codes are available, allowing application to modern data sets. In its original form, the Elixhauser index uses binary indicators for the presence or absence of each comorbidity.

There are two common implementations. The unweighted Elixhauser index tallies the number of present comorbidity categories, producing a count of risk factors. A widely used weighted version, developed by van Walraven and colleagues in 2009, assigns coefficients to each condition to produce a single composite score; higher scores indicate greater comorbidity burden and higher risk of adverse outcomes such as mortality, longer length of stay, or higher costs.

Applications include risk adjustment in studies of hospital mortality, readmission, length of stay, and costs across diverse clinical areas. Limitations include dependence on the accuracy and consistency of coding practices and potential variation across health systems. Software implementations and mappings to ICD-10-CM exist, notably through the Agency for Healthcare Research and Quality and other statistical packages for administrative data analysis.