Original Articles
An adaptation of Charlson comorbidity index predicted subsequent mortality in a health survey

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Abstract

Objective

The Catalan Health Interview Survey Follow-up Study analyzed survival differences according to comorbidity, using an adaptation of the Charlson's index.

Study design and setting

Vital status was ascertained by record linkage with death certificates 5 years after interview. Three thousand one hundred five men and 3,536 women aged 40–84 years old were included in the analysis. Proportional hazards models with age as time scale were used to calculate relative risk (RR) and 95% confidence interval adjusted for potential confounders.

Results

The adjusted RR of death in men was 1.02 (0.73–1.41) for a comorbidity index of 1–2; the RR was 1.51 (1–2.30) for an index of 3–4, and 2.64 (1.43–4.89) for an index of >4 composed to an index of 0. In women, for the same comorbidity index categorization, the RR of death were 0.83 (0.55–1.24), 1.71 (1.09–2.72) and 2.65 (1.47–4.77).

Conclusion

This result confirms the relation between comorbidity and the risk of death based on a comorbidity index that takes into account severity and number of self-declared chronic diseases with mortality.

Introduction

Coexistence of multiple chronic diseases can affect survival depending on type, duration, and severity of the disease. Moreover, chronic diseases could have an additive or multiplicative effect on the risk of dying, having disabilities or using health care services [1].

Current research points out the need of elaborating a composite comorbidity index that assesses the number and severity of chronic diseases and other influent variables like age [2], [3] and gender [1]. One of the most frequently used comorbidity index is that proposed by Charlson and colleagues, which is derived from the weight assigned to the relative risk of dying due to different chronic diseases [4], [5].

In Spain, however, there is a lack of information about the association of self-declared chronic diseases and mortality, given the number of population-based follow-up studies in course [6], [7], [8]. To date, no overall assessment of survival and self-declared chronic diseases has been conducted in Spain.

The aim of this investigation was twofold: first, to adapt a modification of the Charlson comorbidity index of self-declared chronic diseases, and second, to analyze 5-year mortality according to this index in a representative cohort of the non institutionalized population of Catalonia, Spain.

Section snippets

Sample and design of the study

The 1994 Catalan Health Interview Survey (ESCA), which was conducted by the Catalan Health Service, was a cross-sectional survey based on a representative sample of the noninstitutionalized population of Catalonia [9], [10]. The survey collected sociodemographic data and information about chronic conditions, life styles, self-perceived health, health services use, preventive practices, and disability and mental health disorders at the initial time, and it was not assessed again. In brief,

Results

After applying the sampling weights derived from the whole sample stratification, there were a total of 6,641 individuals (3,105 men and 3,536 women). At the end of the follow-up 234 men and 152 women had died. The individuals free of chronic disease were 28.8% for men and 17.2% for women.

For those men who died during the follow-up, the median age at starting of follow-up was 70 years old, and for those censored the median age was 56 years old. Among women a similar pattern was observed: 71

Discussion

After 5 years of follow-up, our study shows that the risk of death increases along with the comorbidity index both in men and women aged 40–84 years old. This result agrees with most studies that have also used Charlson's comorbidity index or different adaptations of it, in different populations, with different methodology and with different adjusting variables [1], [2], [4], [19], [20].

The advantage of using a comorbidity index that summarizes both number of chronic conditions and its severity

Acknowledgements

This study was, in part, supported by the Fondo de Investigación Sanitaria (FIS 98/0053-01) from the Spanish Ministry of Health. Our special acknowledgement to Rosa Lamarca for her suggestions to the last version of the manuscript.

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