Charlson Index Is Associated with One-year Mortality in Emergency Department Patients with Suspected Infection
A patient's baseline health status may affect the ability to survive an acute illness. Emergency medicine research requires tools to adjust for confounders such as comorbid illnesses. The Charlson Comorbidity Index has been validated in many settings but not extensively in the emergency department (ED). The purpose of this study was to examine the utility of the Charlson Index as a predictor of one-year mortality in a population of ED patients with suspected infection. The comorbid illness components of the Charlson Index were prospectively abstracted from the medical records of adult (age older than 18 years) ED patients at risk for infection (indicated by the clinical decision to obtain a blood culture) and weighted. Charlson scores were grouped into four previously established indices: 0 points (none), 1-2 points (low), 3-4 points (moderate), and > or =5 points (high). The primary outcome was one-year mortality assessed using the National Death Index and medical records. Cox proportional-hazards ratios were calculated, adjusting for age, gender, and markers of 28-day in-hospital mortality. Between February 1, 2000, and February 1, 2001, 3,102 unique patients (96% of eligible patients) were enrolled at an urban teaching hospital. Overall one-year mortality was 22% (667/3,102). Mortality rates increased with increasing Charlson scores: none, 7% (95% confidence interval [CI] = 5.4% to 8.5%); low, 22% (95% CI = 19% to 24%); moderate, 31% (95% CI = 27% to 35%); and high, 40% (95% CI = 36% to 44%). Controlling for age, gender, and factors associated with 28-day mortality, and using the "none" group as a reference group, the Charlson Index predicted mortality as follows: low, odds ratio of 2.0; moderate, odds ratio of 2.5; and high, odds ratio of 4.7. This study suggests that the Charlson Index predicts one-year mortality among ED patients with suspected infection.
Charlson Index Is Associated with One-year
Mortality in Emergency Department Patients
with Suspected Infection
Scott B. Murray, MD, David W. Bates, MD, MSc, Long Ngo, PhD, Jacob W. Ufberg, MD,
Nathan I. Shapiro, MD, MPH
Objectives: A patient’s baseline health status may affect the ability to survive an acute illness. Emergency
medicine research requires tools to adjust for confounders such as comorbid illnesses. The Charlson
Comorbidity Index has been validated in many settings but not extensively in the emergency department
(ED). The purpose of this study was to examine the utility of the Charlson Index as a predictor of one-
year mortality in a population of ED patients with suspected infection.
Methods: The comorbid illness components of the Charlson Index were prospectively abstracted from the
medical records of adult (age older than 18 years) ED patients at risk for infection (indicated by the clinical
decision to obtain a blood culture) and weighted. Charlson scores were grouped into four previously estab-
lished indices: 0 points (none), 1–2 points (low), 3–4 points (moderate), and R5 points (high). The primary
outcome was one-year mortality assessed using the National Death Index and medical records. Cox
proportional-hazards ratios were calculated, adjusting for age, gender, and markers of 28-day in-hospital
Results: Between February 1, 2000, and February 1, 2001, 3,102 unique patients (96% of eligible patients)
were enrolled at an urban teaching hospital. Overall one-year mortality was 22% (667/3,102). Mortality
rates increased with increasing Charlson scores: none, 7% (95% conﬁdence interval [CI] = 5.4% to
8.5%); low, 22% (95% CI = 19% to 24%); moderate, 31% (95% CI = 27% to 35%); and high, 40% (95%
CI = 36% to 44%). Controlling for age, gender, and factors associated with 28-day mortality, and using
the ‘‘none’’ group as a reference group, the Charlson Index predicted mortality as follows: low, odds ratio
of 2.0; moderate, odds ratio of 2.5; and high, odds ratio of 4.7.
Conclusions: This study suggests that the Charlson Index predicts one-year mortality among ED patients
with suspected infection.
ACADEMIC EMERGENCY MEDICINE 2006; 13:530–536 ª 2006 by the Society for Academic Emergency
Keywords: mortality prediction, risk adjustment, emergency medicine, sepsis
t is intuitive that a patient’s baseline health status
plays a role in a patient’s ability to survive after sus-
taining an acute injury or illness.
fying a patient’s comorbid burden can be difﬁcult. The
challenge lies in determining which comorbid conditions
affect patient mortality and to what degree. Charlson
et al. developed a scoring system for comorbid illness
that predicted one-year mortality in medical inpatients
and later validated the model in patients with breast can-
The Charlson score is based on the presence of clin-
ical conditions obtained from manual chart abstraction.
Each comorbid condition was assigned a whole number
integer that was proportional to the relative risk of death
(at one year) associated with that disease (Table 1). The
sum of the integers makes up the Charlson score, and
the scores are grouped to form the Charlson Index.
The importance of accurately measuring comorbidity
is apparent when researchers attempt to describe the
baseline illness severity in a patient population. A stan-
dardized tool that calculates a patient’s baseline disease
severity would be useful for researchers, because it
From the Department of Emergency Medicine, Beth Israel
Deaconess Medical Center (SBM, LN, NIS), Boston, MA; Division
of General Medicine, Department of Medicine, Brigham and
Women’s Hospital (DWB), Boston, MA; and Department of Emer-
gency Medicine, Temple University Hospital (JWU), Philadelphia,
Received July 24, 2005; revision received November 14, 2005;
accepted November 14, 2005.
Address for correspondence and reprints: Nathan I. Shapiro,
MD, MPH, West Clinical Center 2–Department of Emergency
Medicine, Beth Israel Deaconess Medical Center, One Deaconess
Way, Boston, MA 02215. Fax: 617-754-2350; e-mail: nshapiro@
ISSN 1069-6563 ª 2006 by the Society for Academic Emergency Medicine
PII ISSN 1069-6563583 doi: 10.1197/j.aem.2005.11.084530
would allow readers to better understand the comorbid
burden in the study population and to assess the general-
izability of the study to the reader’s patient population.
It could also be useful to analyze comorbid burden as a
potential confounder to study results, similar to what
would occur when discrepancies in age, race, or gender
are found between cohorts. Such a tool would also be of
value in small case series and nonrandomized studies.
Researchers could use this as a tool to describe popula-
tions when comparing data between different institu-
tions or time periods. This tool could also be used to
gauge the success of randomization.
The Charlson Index is a well-validated research metho-
dology that has been used in numerous populations.
Despite its prevalence in the medical literature, the utility
of the Charlson Index has not been well studied in an
emergency department (ED) population.
we sought to determine how well the Charlson Index
would predict one-year mortality in a population of ED
patients with suspected infection.
We performed an observational study of consecutive ED
patients with suspected infection seen over a one-year
period to assess the ability of the Charlson Comorbidity
Index to predict mortality. The primary outcome mea-
sured was one-year mortality. This study was approved
by the investigational review board at Beth Israel
Deaconess Medical Center.
Study Setting and Population
Subjects were patients seen at an urban, academic, ter-
tiary care hospital ED in Boston with an annual census
of 50,000 visits. The study period began on February 1,
2000, and ended on February 1, 2001. All patients (18
years or older) who had blood cultures drawn in the
ED (or within three hours of admission to an inpatient
bed) were eligible for the study.
Patients who had
more than one ED visit during the study period were
enrolled only once at the ﬁrst visit. The clinical decision
to obtain a blood culture was used to identify patients
deemed at risk for infection, because clinicians com-
monly obtain blood cultures on patients who are
suspected to have bacteremia.
Study Protocol and Measurements
Emergency department charts were reviewed by trained
data abstractors without subsequent knowledge of the
patient’s hospital course or the study hypothesis. Data
collected included demographic information and the
presence of any of the Charlson comorbidities. Original
deﬁnitions and integer weights of comorbid conditions,
as published by Charlson et al., were used (Table 1).
Charlson score was calculated for each patient by adding
the integers (Table 1) assigned to each disease diagnosed
in that patient (e.g., congestive heart failure  + lym-
phoma  = Charlson score ). The Charlson score
was prospectively consolidated into four previously
deﬁned groups known as the Charlson Index: 0 points
(none), 1–2 points (low), 3–4 points (moderate), and R5
points (high) as originally described.
One-year mortality (measured from date of index visit)
was used as the primary mortality outcome, because the
Charlson Index was originally derived for this time inter-
val. Patients were classiﬁed as dead (22%) if they were
found to be on the national death registry within one
year from the index visit or if they had a discharge diag-
nosis of death during the one-year period. Patients were
conﬁrmed to be alive (53%) if they were found to have
had a hospital encounter (laboratory tests, ofﬁce visits,
and so on) more than one year after the index visit. Pa-
tients were presumed to be alive (25%) if they were not
located in the national death registry (no evidence of
death) and did not have any hospital encounters (no evi-
dence of life). Both conﬁrmed and presumed alive were
classiﬁed as alive for the purposes of analysis.
Descriptive statistics were used to summarize the demo-
graphics and in-hospital clinical characteristics of 3,102
patients eligible for the analysis. Categorical variables
were reported as percentages. The distributions of con-
tinuous variables were described using the mean, stan-
dard deviation, and median with interquartile ranges.
One-year mortality rates with 95% conﬁdence intervals
(CIs) were calculated for each Charlson Index group.
To determine independent association of the Charlson
Index with one-year mortality, we built a Cox propor-
tional-hazards model incorporating routinely reported
variables (age, gender) and signiﬁcant predictors of
28-day in-hospital mortality identiﬁed in prior studies.
The Cox proportional-hazards model was used to com-
pare the adjusted one-year mortality hazard ratios for
the Charlson Index using the lowest comorbidity (none)
as the reference group. Adjusted relative hazard ratio
estimates with corresponding 95% CIs were reported
for the three Charlson Comorbidity Index groups (low,
moderate, and high). Our new model showing adjusted
relative hazard ratios includes covariates found to be
independent predictors of one-year mortality (p < 0.05).
Charlson Comorbid Conditions
Acquired immunodeﬁciency syndrome 6
Metastatic solid tumor 6
Moderate or severe liver disease 3
Diabetes with end organ damage 2
Hemiplegia, paraplegia 2
Nonmetastatic solid tumor, leukemia,
Renal disease 2
Cerebrovascular accident 1
Chronic pulmonary disease 1
Congestive heart failure 1
Connective tissue disease 1
Diabetes without organ damage 1
Mild liver disease 1
Myocardial infarction 1
Peptic ulcer disease 1
Peripheral vascular disease 1
ACAD EMERG MED
May 2006, Vol. 13, No. 5
The Kaplan–Meier estimation method was used to obtain
the survival distribution estimates. All analyses were per-
formed using SAS software version 9 (SAS Institute, Inc.,
Over a one-year period, 4,044 patient visits occurred
during which blood cultures were drawn. Repeat visits
occurred in 824 cases, and only the ﬁrst visit was eligible
for inclusion. Of the 3,220 eligible patient visits, 3,102
were enrolled (96% of eligible patients). Using medical
records, 53% were found to be alive one year later, while
22% had died as determined by medical records or
the national death index. Twenty-ﬁve percent of the study
group was presumed to be alive because no evidence of
death was found in the national death index. The average
age was 59.9 years (median, 61 years). Female patients
made up a slightly larger proportion than male patients
(Table 2). The median length of stay in the hospital was
three days, and 11.6% were admitted to the intensive
care unit (median length of stay in the intensive care
unit, two days). The most frequent suspected sources of
infection, as documented by the treating physician,
were lower respiratory infections and skin/soft tissue
infections (Table 2).
Table 2 also shows the prevalence of baseline comor-
bid conditions, as deﬁned by the Charlson Comorbidity
Index. The categories of nonmetastatic solid tumor, con-
gestive heart failure, renal disease, and chronic pulmo-
nary diseases make up slightly more than half of all the
comorbidities listed. All comorbidity index groups were
represented: none, 32%; low, 34%; moderate, 17%; and
The one-year unadjusted mortality rate increased as
Charlson Index severity increased: none, 7% (95% CI =
5.4% to 8.5%); low, 22% (95% CI = 19% to 24%); moder-
ate, 31% (95% CI = 26.8% to 34.7%); and high, 40%
(95% CI = 35.5% to 43.8%) (Table 3). Survival over time
(Kaplan–Meier method) decreased with increasing Charl-
son Index severity (Figure 1). Table 3 shows the observed
incidence of death at one year stratiﬁed by the Charlson
Comorbidity Index, gender, and age. There is not a sig-
niﬁcant difference in mortality between the two genders.
The adjusted survival analysis model shows the indepen-
dent effect of the Charlson Comorbidity Index on mor-
tality after controlling for gender, age, and factors that
were found to be predictive of inpatient 28-day mortality
(nursing home residents, lower respiratory infection,
respiratory rate >20 breaths/min or pulse oximetry
<90%, altered mental status, and platelet count <150,000/
mL). Age was strongly correlated with mortality risk, but
even after adjusting for age the Charlson Index remained
strongly predictive of mortality. Using the Charlson
Index group with the lowest comorbidity (none) as the
reference group (odds ratio of 1), the adjusted odds of
death for each group were as follows: low, odds ratio
of 2.0 (95% CI = 1.6 to 2.7), moderate, odds ratio of 2.5
(95% CI = 1.9 to 3.4), and high, odds ratio of 4.7 (95%
CI = 3.6 to 6.2). Adjusted odds ratios were statistically dif-
ferent using the Cox proportional-hazards model. Each
index group was an independent predictor of death,
with risk progressively increasing as Charlson Index
Descriptive Statistics of Patient Population
Demographic and admission
Percent female (n) 55 (1,706)
Median (IQR) age (yr) 61 (43–77)
Median (IQR) length of stay (days) 3.0 (1–6)
ICU admission rate (n) 11.6 (360)
Median (IQR) ICU length of stay (days) 2.0 (1–5)
Indication for blood cultures (% [n])
Lower respiratory infection 23 (719)
Skin or soft tissue infection 19 (590)
Intra-abdominal infection 14 (424)
Fever without source 13 (414)
Urologic infection 10 (296)
Line infection 4 (117)
Central nervous system infection 2 (74)
Rule out endocarditis 2 (65)
Neutropenic fever 2 (61)
Charlson comorbid conditions (% [n])
Nonmetastatic solid tumor, leukemia, lymphoma 19 (605)
Congestive heart failure 13 (425)
Renal disease 10 (366)
Chronic pulmonary disease 11 (360)
Diabetes without organ damage 12 (351)
Diabetes with end organ damage 10 (341)
Myocardial infarction 9 (288)
Cerebrovascular accident 8 (257)
Dementia 8 (257)
Peripheral vascular disease 7 (233)
Acquired immunodeﬁciency syndrome 6 (217)
Peptic ulcer disease 5 (174)
Moderate or severe liver disease 4 (158)
Metastatic solid tumor 4 (152)
Mild liver disease 2 (65)
Connective tissue disease 2 (62)
Hemiplegia, paraplegia 1 (34)
Patients may have more than one comorbidity, so the totals may be
One-year Mortality Stratiﬁed by Charlson Index, Gender, and
None (0) 7.0 1.0
Low (1–2) 22 2.0 (1.6, 2.7)
Moderate (3–4) 31 2.5 (1.9, 3.4)
High (R5) 40 4.7 (3.6, 6.2)
Female 21 1.0
Male 22 1.1 (0.9, 1.3)
Younger than 65 11 1.0
Between 65 and 80 29 2.1 (1.7, 2.6)
Older than 80 42 2.8 (2.3, 3.5)
* Cox proportional-hazards model, adjusted for gender, age, and signiﬁ-
cant covariates: nursing home residents, lower respiratory infection, res-
piratory rate >20 breaths/min or pulse oximetry <90%, altered mental
status, and platelet count <150,000/mL.
532 Murray et al.
CHARLSON INDEX AND ONE-YEAR MORTALITY IN ED PATIENTS
We found that the Charlson Index was a valid predictor
of one-year mortality in an ED patient population, inde-
pendent of age and gender. The index was able to quan-
tify the comorbid status of this population. These data
suggest that researchers can use this index to assess if
study cohorts have similar comorbid burdens or if in
fact there is excess comorbidity that may act as a con-
founder. This is particularly important when comparing
research between different studies or data obtained
from populations at different institutions. Investigators
can also verify if randomization has equally distributed
comorbidity between cohorts.
If cohorts are dissimilar, adjustment may be made to
account for baseline comorbidity. This tool may help
researchers assess population equality when performing
small nonrandomized studies or case series. In fact, the
Charlson Index has been used as a primary outcome,
an independent variable, and as a way to control for
comorbid illness for a variety outcomes besides mor-
Assuming that patients with more comorbid disease
will have higher mortality rates, the ability of the Charl-
son Index to measure comorbidity may be veriﬁed by
plotting mortality rates against the Charlson Index and
then observing a progressive increase in mortality. The
original investigation used to derive the Charlson Index
predicted one-year mortality in medical inpatients in
1984 as follows: 12%, none; 26%, low; 52%, moderate;
and 85%, high. The same index predicted different rates
of one-year mortality in the validation group of patients
with breast cancer between 1962 and 1969 as follows:
1%, none; 3%, low; 16%, moderate; and 31%, high.
Our work shows that the Charlson Index predicted
one-year mortality due to comorbid conditions in a dif-
ferent population, ED patients with suspected infection,
as follows: 7%, none; 22%, low; 31%, moderate; and
40%, high. It is inherent that the absolute mortality rates
will vary between populations presenting with different
acute diseases, and researchers should not apply the
mortality rates of patients at risk for sepsis to their
cohorts with different acute medical problems. However,
as this ED study and numerous studies from other
patient populations have demonstrated the ability of the
Charlson Index to predict one-year mortality, it is likely
that the model can assess comorbidity in other ED
patient cohorts, albeit with differing absolute mortality
Some have commented that age alone may be a sufﬁ-
cient surrogate marker for comorbidity when trying to
assess cohort similarity.
In the only previous study
examining the Charlson Index in an ED population, the
Charlson Index was found to be equivalent to the modi-
ﬁed Trauma and Injury Severity Score (modiﬁed using
age as a continuous variable) in predicting Australian
inpatient mortality after acute trauma.
We found age
to be an important predictor of mortality but that comor-
bidity is an independent and equally important predictor.
Instinctively, clinicians realize that despite advanced age,
a 72-year-old patient with a history of hypertension may
fare better than a 45-year-old patient with diabetes, renal
failure, prior myocardial infarction, and chronic obstruc-
tive pulmonary disease. Ignoring the effect of comorbid-
ity on mortality could potentially produce as much bias
as if age were ignored. To detect potential confounders,
researchers report the similarity between cohorts; data
on age, gender, and severity of acute illness are routinely
presented. Given the results of this study, researchers
Figure 1. Observed survival distributions estimated by Kaplan–Meier product limit method for each of the four categories of
the Charlson Index over time. The four categories of the Charlson Index display four distinct survival distributions that are
further apart toward the end of the one-year follow-up period, indicating stronger association between the index and mor-
tality through time. The log-rank test for differences between the groups is statistically signiﬁcant (p < 0.001).
ACAD EMERG MED
May 2006, Vol. 13, No. 5
may wish to comment on comorbidity equality between
populations using the Charlson Index in future studies.
We used the original integer weights as initially de-
scribed by Charlson et al. When the weights for the score
are rederived based on data speciﬁc to a particular pop-
ulation, the index becomes more accurate when used
with that population.
This probably reﬂects the
impact a given comorbid condition has on a particular
disease cohort (e.g., congestive heart failure has an inte-
ger weight of 3 when the model is rederived in patients
undergoing coronary artery bypass graft surgery).
Rederivation also reﬂects regional differences that
make study populations different. The utility of using
the original Charlson weighting system is that it can be
(and has been successfully) applied to many populations,
but this generalizability diminishes its ‘‘goodness of ﬁt’’
to any speciﬁc population. Rederiving the weighting of
comorbid factors based on local patient demographic
and hospital characteristics would make the tool more
speciﬁc to the area where it was created. This is advanta-
geous for the researcher locally, but disadvantageous
when trying to create a more universal tool. Theoreti-
cally, researchers would have to collect large amounts
of data, rederive, and validate a model every time a
new population (new hospital, different presenting dis-
ease, and so on) was studied, which is an expensive,
This study has several limitations. Free-text ED charts
were used for data abstraction, and it is likely that
more medical history became available after admission
or that documentation inaccuracies occurred, creating
misclassiﬁcation bias for the variables. The model may
have performed better had clinicians been required to
specify the presence or absence of each Charlson Index
component or had inpatient charts been used. However,
this limitation shows that researchers who only have ac-
cess to ED charts can assess comorbidity adequately with
the information at hand. Future work that includes inpa-
tient chart data may increase the accuracy of the Charl-
son score. Misclassiﬁcation bias in assessing mortality
is possible; however, we conﬁrmed life or death in 75%
of the study group and assumed the remaining 25% to
be alive because they were not listed in the national death
index. External validity was not addressed because data
were collected from only one hospital site.
Future research may include using inpatient records to
more accurately assess comorbid disease or rederiving
the integer weights. The Charlson Index has been previ-
ously adapted to ICD-9-CM inpatient databases.
utility of using computerized administrative databases to
determine comorbidity has not been examined in an ED
We found that the Charlson Index, a well-established
method to assess for comorbid illness burden, predicted
one-year mortality for an ED patient population with
suspected infection. The Charlson Index may be used
by researchers to measure comorbidity and assess co-
hort similarity or to control for a patient’s comorbidity.
Further validation in other ED patient populations
should be performed before widespread implementation.
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536 Murray et al.
CHARLSON INDEX AND ONE-YEAR MORTALITY IN ED PATIENTS