Elixhauser Comorbidity Index

The Elixhauser Comorbidity Index identifies 31 comorbidity categories that affect hospital outcomes, resource utilization, and mortality.

Overview

The Elixhauser index was developed in 1998 as a more comprehensive alternative to the Charlson index, capturing a broader range of comorbid conditions.

Supported Mappings

Mapping	ICD-9	ICD-10	Description
`quan`	✅	✅	Quan et al. enhanced ICD coding

Weighting Schemes

Weighting	Description
`van_walraven`	van Walraven et al. (2009) - mortality prediction
`swiss`	Swiss adaptation for mortality prediction

Comorbidity Categories

The Elixhauser index identifies 31 comorbidity categories:

Abbreviation	Condition
`chf`	Congestive heart failure
`carit`	Cardiac arrhythmias
`valv`	Valvular disease
`pcd`	Pulmonary circulation disorders
`pvd`	Peripheral vascular disorders
`hypunc`	Hypertension, uncomplicated
`hypc`	Hypertension, complicated
`para`	Paralysis
`ond`	Other neurological disorders
`cpd`	Chronic pulmonary disease
`diabunc`	Diabetes, uncomplicated
`diabc`	Diabetes, complicated
`hypothy`	Hypothyroidism
`rf`	Renal failure
`ld`	Liver disease
`pud`	Peptic ulcer disease (excluding bleeding)
`aids`	AIDS/HIV
`lymph`	Lymphoma
`metacanc`	Metastatic cancer
`solidtum`	Solid tumor without metastasis
`rheumd`	Rheumatoid arthritis/collagen vascular
`coag`	Coagulopathy
`obes`	Obesity
`wloss`	Weight loss
`fed`	Fluid and electrolyte disorders
`blane`	Blood loss anemia
`dane`	Deficiency anemia
`alcohol`	Alcohol abuse
`drug`	Drug abuse
`psycho`	Psychoses
`depre`	Depression

Usage

Python API

import polars as pl
from comorbidipy import comorbidity, ScoreType, WeightingVariant

df = pl.DataFrame({
    "patient_id": ["P001", "P001", "P002", "P002"],
    "icd_code": ["I50", "E11", "F32", "J44"],
})

# Basic Elixhauser calculation
result = comorbidity(
    df,
    id_col="patient_id",
    code_col="icd_code",
    score=ScoreType.ELIXHAUSER,
)

# With van Walraven weights
result = comorbidity(
    df,
    id_col="patient_id",
    code_col="icd_code",
    score=ScoreType.ELIXHAUSER,
    weighting=WeightingVariant.VAN_WALRAVEN,
)

# With Swiss weights
result = comorbidity(
    df,
    id_col="patient_id",
    code_col="icd_code",
    score=ScoreType.ELIXHAUSER,
    weighting=WeightingVariant.SWISS,
)

CLI

# Basic Elixhauser calculation
comorbidipy elixhauser input.csv output.csv

# With van Walraven weights
comorbidipy elixhauser input.parquet output.parquet --weights van_walraven

# With Swiss weights
comorbidipy elixhauser input.csv output.csv --weights swiss

Assign Zero Logic

By default (assign0=True), when a more severe or complicated form of a condition is present, the uncomplicated form is set to 0:

hypunc (uncomplicated hypertension) → 0 if hypc (complicated) present
diabunc (uncomplicated diabetes) → 0 if diabc (complicated) present
solidtum (solid tumor) → 0 if metacanc (metastatic) present

To keep both forms:

result = comorbidity(df, assign0=False)

Output

The output DataFrame includes: - Patient ID column - Binary columns (0/1) for each of the 31 comorbidity categories - comorbidity_score: Weighted sum of comorbidities

van Walraven Weights

The van Walraven weighting scheme assigns the following weights to predict in-hospital mortality:

Condition	Weight
Congestive heart failure	7
Cardiac arrhythmias	5
Valvular disease	-1
Pulmonary circulation disorders	4
Peripheral vascular disorders	2
Hypertension, uncomplicated	0
Hypertension, complicated	0
Paralysis	7
Other neurological disorders	6
Chronic pulmonary disease	3
Diabetes, uncomplicated	0
Diabetes, complicated	0
Hypothyroidism	0
Renal failure	5
Liver disease	11
Peptic ulcer disease	0
AIDS/HIV	0
Lymphoma	9
Metastatic cancer	12
Solid tumor	4
Rheumatoid arthritis	0
Coagulopathy	3
Obesity	-4
Weight loss	6
Fluid and electrolyte disorders	5
Blood loss anemia	-2
Deficiency anemia	-2
Alcohol abuse	0
Drug abuse	-7
Psychoses	0
Depression	-3

Note that some weights are negative, reflecting protective associations in the original study.

References

Elixhauser A, et al. Comorbidity measures for use with administrative data. Med Care. 1998;36(1):8-27.
van Walraven C, et al. A modification of the Elixhauser comorbidity measures into a point system for hospital death using administrative data. Med Care. 2009;47(6):626-633.