Comorbidity Assessment
The Charlson Comorbidity Index and family history
Overview
The comorbidity factor (C) measures the burden of chronic conditions you have been diagnosed with, plus a small contribution from your family history. It runs from 0 (no conditions) to 1 (a heavy burden).
Updated October 2026 for scoring model v0.2.0. An earlier version of this post described v0.1.0’s model, which v0.2.0 replaced.
The Charlson Comorbidity Index
The Charlson Comorbidity Index (CCI) is a widely used clinical tool. It gives chronic conditions a weight by how strongly they predict mortality:
| Weight | Examples |
|---|---|
| 1 | Heart attack, heart failure, peripheral vascular disease, stroke, dementia, COPD, uncomplicated diabetes |
| 2 | Hemiplegia, moderate or severe kidney disease, diabetes with organ damage, tumors, leukemia, lymphoma |
| 3 | Moderate or severe liver disease |
| 6 | Metastatic solid tumor, AIDS |
Conditions without a Charlson weight, such as mental health conditions, add nothing here. Mental health is part of the health factor instead.
How C is calculated
We add up the Charlson weights of the conditions you report, plus a family-history amount, and divide by 10:
\[ C = \min\left(1,\; \frac{\text{Charlson total}}{10}\right) \]
A total of 10 or more gives C = 1.
Family history
Family history adds a small amount for each condition that has a genetic component:
- Each condition counts once, however many relatives have it.
- Conditions you have yourself aren’t counted again.
- Each adds its Charlson weight (at least 1) times a small family weight, typically 1% of what the same condition adds when you have it yourself.
Family history also adds to the risk factor, at half the weight of your own conditions. See Risk Factor Assessment.
How C affects your score
C sets the starting level of your lifetime health curve:
\[ \text{score}(\text{age}) = -\alpha R \cdot \text{age}^2 + \beta H \cdot \text{age} + \gamma C \]
In the current calibration (January 2026), γ is small, so C moves a score by less than 3 points. Your conditions also add to the risk factor, which has a larger effect. We are reviewing how C should count as scores come in.
Limitations
- Self-report: we rely on the conditions you tell us about.
- Population: the CCI was developed mainly in Western hospital populations.
- Validation: the model was calibrated on test surveys. It has not yet been validated against clinical outcomes; we plan to do that as real scores accumulate.
Open source
The scoring code is open source under the MIT licence: github.com/preacterik/preact-health-scoring.
References
- Charlson ME, et al. A new method of classifying prognostic comorbidity in longitudinal studies. Journal of Chronic Diseases (1987).
- Quan H, et al. Updating and validating the Charlson Comorbidity Index and score for risk adjustment in hospital discharge abstracts. American Journal of Epidemiology (2011).