ElixhauserScore

ElixhauserScore, commonly referred to as the Elixhauser comorbidity index, is a method used to quantify a patient’s burden of comorbidity from administrative data. It was introduced by Anne Elixhauser and colleagues in 1998 and comprises 30 diagnosis-based comorbidity categories derived from ICD-9-CM codes. The approach is designed to capture a broad range of chronic and acute conditions and is widely used for risk adjustment in outcomes research. With the transition to ICD-10-CM/PCS, researchers have adapted the coding mappings to enable calculation across modern datasets, including inpatient and outpatient encounters.

Calculation and interpretation: In its original form the 30 comorbidities are recorded as present or absent for a patient, and researchers may either sum these indicators to create a simple comorbidity burden score or apply a post hoc weighting system. The most common weighting comes from van Walraven and colleagues (2009), which assigns weights to each condition to produce a single composite score predicting in-hospital mortality and other outcomes. In practice, higher Elixhauser scores indicate greater comorbidity burden and higher anticipated risk. Some studies report separate binary indicators or subgroup analyses rather than a single weighted score, depending on the research question and data source.

Limitations and related measures: The validity of the ElixhauserScore depends on accurate coding and consistent coding practices; differences in ICD versions, hospital coding policies, or payer requirements can affect scores and comparisons over time or across settings. It is a risk-adjustment tool rather than a causal measure of outcomes and is often used alongside other indices such as the Charlson comorbidity index.