Elixhauser

The Elixhauser comorbidity index, often referred to simply as the Elixhauser index, is a method for measuring patient comorbidity burden using administrative hospital data. It was developed in 1998 by Anne Elixhauser and colleagues to improve risk adjustment for hospital outcomes. The original index identifies 30 distinct comorbid conditions from ICD-9-CM diagnosis codes, with each condition coded as a binary variable (present or absent). The conditions cover a wide range of chronic diseases, including congestive heart failure, chronic pulmonary disease, diabetes with and without complications, renal failure, liver disease, cancer, obesity, and others. Unlike some other measures, the original Elixhauser approach does not assign a single aggregate weight to the combined comorbidity burden; rather, it provides a set of indicators that can be used in statistical models.

In 2009, van Walraven and colleagues proposed a weighted version of the Elixhauser comorbidity index designed to optimize prediction of in-hospital mortality. Weights are applied to each condition to produce a single score; this weighted index has been widely adopted in applied research for risk adjustment beyond mortality, including length of stay and costs.

With the transition from ICD-9-CM to ICD-10-CM coding systems, the Elixhauser definitions have been mapped to ICD-10-CM, enabling contemporary use in electronic health records and administrative datasets.

Compared with the Charlson Comorbidity Index, the Elixhauser set is generally considered more comprehensive and flexible, often yielding improved predictive performance for a range of outcomes, though performance can vary by setting and outcome.