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Relative Impact of Risk Factors for Deep Vein Thrombosis and Pulmonary Embolism
A Population-Based Study
John A. Heit, MD;
W. Michael O'Fallon, PhD;
Tanya M. Petterson, MS;
Christine M. Lohse, BS;
Marc D. Silverstein, MD;
David N. Mohr, MD;
L. Joseph Melton III, MD
Arch Intern Med. 2002;162:1245-1248.
ABSTRACT
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Objective To assess the potential impact of controlling risk factors on the incidence
of venous thromboembolism by estimating the population attributable risk (defined
as the percentage of all cases of a disease in a population that can be "attributed"
to a risk factor) for deep vein thrombosis and pulmonary embolism associated
with venous thromboembolism risk factors.
Methods Using data from a population-based, nested, case-control study of the
625 Olmsted County, Minnesota, residents with a definite first lifetime deep
vein thrombosis or pulmonary embolism diagnosed during the 15-year period
1976 to 1990 and 625 unaffected Olmsted County residents matched for age and
sex, we developed a conditional logistic regression model appropriate to the
matched case-control study design and then estimated attributable risk for
the risk factors individually and collectively.
Results Fifty-nine percent of the cases of venous thromboembolism in the community
could be attributed to institutionalization (current or recent hospitalization
or nursing home residence). Hospitalization for surgery (24%) and for medical
illness (22%) accounted for a similar proportion of the cases, while nursing
home residence accounted for 13%. The individual attributable risk estimates
for malignant neoplasm, trauma, congestive heart failure, central venous catheter
or pacemaker placement, neurological disease with extremity paresis, and superficial
vein thrombosis were 18%, 12%, 10%, 9%, 7%, and 5%, respectively. Together,
the 8 risk factors accounted for 74% of disease occurrence.
Conclusions Factors associated with institutionalization independently account for
more than 50% of all cases of venous thromboembolism in the community. Greater
emphasis should be placed on prophylaxis for hospitalized medical patients.
Other recognized risk factors account for about 25% of all cases of venous
thromboembolism, while the remaining 25% of cases are idiopathic.
INTRODUCTION
VENOUS THROMBOEMBOLISM (ie, deep vein thrombosis and its complication,
pulmonary embolism) is a common disease, with an average annual incidence
rate of more than 1 per 1000.1 Venous thromboembolism
also is a lethal disease, mostly owing to pulmonary embolism. The 1-week survival
rate after a pulmonary embolism is only 71%, and almost 25% of all cases of
pulmonary embolism essentially present as sudden death.2
Survivors may experience serious and costly long-term complications. Almost
30% of patients develop serious venous stasis syndrome within 10 years,3-4 at an estimated cost of more than $4000
per episode in 1997 dollars.5 To improve survival
and to prevent complications, the occurrence of venous thromboembolism must
be reduced. Independent risk factors for venous thromboembolism have been
identified,6 and effective prophylaxis is available
for certain subgroups.7 However, the incidence
of venous thromboembolism, both arising in the hospital as well as in the
general population, has remained relatively constant since about 1980.1, 8 This could reflect either an increase
in the population at risk (eg, an increase in the average population age)
or exposure of the population to more or new risk factors (eg, an increase
in surgical procedures).9 Additional possibilities
include inadequate identification of high-risk populations and underuse of
appropriate prophylaxis.10-11
To address the potential impact of universal prophylaxis or modification of
currently recognized risk factors (if either were possible) on the incidence
of venous thromboembolism in the community, we used data from a population-based
case-control study6 to estimate the population
attributable risk (defined as the percentage of all cases of a disease in
a population that can be "attributed" to a risk factor) for venous thromboembolism
associated with specific risk factors, both individually and for all risk
factors collectively, while adjusting for other factors.
PATIENTS AND METHODS
STUDY SETTING AND DESIGN
Using the data resources of the Rochester Epidemiology Project,12 we identified the inception cohort of Olmsted County,
Minnesota, residents with a first lifetime deep vein thrombosis or pulmonary
embolism during a 25-year period (1966-1990), as previously described.1 We then performed a case-control study nested within
the Olmsted County population, also as previously described.6
All 625 Olmsted County residents with a first lifetime definite deep vein
thrombosis or pulmonary embolism diagnosed during the 15-year period 1976
to 1990 were included as cases. The Rochester Epidemiology Project also provides
an enumeration of the population from which controls can be sampled as described
elsewhere.12 Using this system, the age (±5
years)-, sex-, and event year (±1 year)–matched Olmsted County
resident whose medical record number was closest to each case's medical record
number was selected as a control. Data were obtained by review of all medical
records (inpatient and outpatient) in the community for each subject.13 The overall mean duration of prior medical record
documentation was 34.7 years (34.7 years for cases and 34.7 years for controls).
Our sample size provided us with at least 80% power to detect a 2-fold increase
in risk for risk factors occurring in more than 5% of the population or a
50% increase in risk for factors occurring in more than 20% of the population.
The study was approved by the institutional review board of the Mayo Clinic,
Rochester.
DEFINITION OF TERMS
The definitions of definite deep vein thrombosis and of definite pulmonary
embolism have been previously described.1 Briefly,
a deep vein thrombosis was categorized as definite when confirmed by venography,
computed tomographic scan, magnetic resonance imaging scan, or the findings
of pathologic examination of a thrombus that had been removed at surgery or
autopsy. A pulmonary embolism was categorized as definite when confirmed by
pulmonary angiography, computed tomographic scan, magnetic resonance imaging
scan, or the findings of pathologic examination of a thrombus that had been
removed at surgery or autopsy. Mayo Clinic pathologists performed all autopsy
examinations and completed the death certificates of the persons who died
within Olmsted County during the study period.
RISK FACTORS FOR VENOUS THROMBOEMBOLISM
A large number of baseline characteristics were tested as potential
risk factors for deep vein thrombosis and pulmonary embolism in a multivariate
conditional logistic regression model, as previously reported.6
Independent risk factors for venous thromboembolism included age at incident
venous thromboembolism event; male sex; calendar year; institutionalized at
onset (eg, hospitalized or in a nursing home or hospitalized within the previous
90 days [with and without surgery]); active malignant neoplasm (with and without
chemotherapy); congestive heart failure; serious neurological disease resulting
in lower extremity paresis; major fracture or severe soft tissue injury; central
vein catheterization or transvenous pacemaker placement; prior superficial
vein thrombosis; varicose veins; and serious liver disease.
ANALYSIS
The development of the final multivariate logistic regression model
referred to above has been described in detail.6
As outlined by Bruzzi et al14 and Benichou
and Gail15 and discussed in detail by Kahn
et al,16 such a logistic model can be used
to estimate attributable risk for individual risk factors, or for several
risk factors collectively, while adjusting for appropriate covariates.
As described by Kahn et al,16 this generalized
attributable risk estimate, , takes on the following
form:
where n is the number of cases in the case-control
study, is the estimated parameter vector from the logistic model,
and i is the difference between the observed and target
vectors for the ith case.
Thus, after fitting the logistic model, the calculation of involves only
the cases. Bootstrap methodology was used to obtain 95% CI estimates of as described by Kahn and coworkers.
RESULTS
The attributable risk estimates associated with the independent risk
factors for venous thromboembolism are shown in Table 1. After adjusting for only the matching variables, we estimated
that 61% (95% confidence interval [CI], 57%-66%) of all cases of definite
venous thromboembolism could be attributed to institutionalization (current
hospital or nursing home confinement or such confinement within the preceding
3 months). After adjusting for all variables in the final model,6
59% of incident venous thromboembolism cases could be attributed to institutionalization.
This estimate can be partitioned into the proportions attributable to hospitalization
with surgery (24%), other hospitalizations (22%), and nursing home residence
(13%).
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Adjusted Population Attributable Risk (AR) Associated With Independent
Risk Factors for First Lifetime Definite Venous Thromboembolism Among Olmsted
County, Minnesota, Residents (1976-1990)*
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Eighteen percent of incident venous thromboembolism cases were attributable
to active malignant neoplasm, with or without chemotherapy (Table 1). Malignant neoplasm without chemotherapy was responsible
for a larger percentage of the risk of venous thromboembolism (12%) than was
malignancy with chemotherapy (6%). Trauma, congestive heart failure, and prior
central venous catheter or pacemaker placement were responsible for 12%, 10%,
and 9% of the venous thromboembolism cases, respectively (Table 1). Seven percent of venous thromboembolism cases were attributable
to neurological disease and 5% to prior superficial vein thrombosis. We initially
estimated that 6% of the cases of venous thromboembolism were attributable
to varicose veins or vein stripping. However, after adjusting for the other
risk factors, none (95% CI, 0%-10%) of the incident venous thromboembolism
cases could be attributed to varicose veins or vein stripping.
The percentages of incident venous thromboembolism cases attributed
to combinations of individual risk factors (after adjusting for the final
model) are illustrated in Figure 1.
For example, institutionalization and malignant neoplasm jointly accounted
for 65% (95% CI, 60%-69%) of the incident venous thromboembolism cases. Thus,
malignant neoplasm can be thought of as having contributed an additional 6%
to venous thromboembolism once we accounted for hospitalization or nursing
home residency (which accounted for 59% alone) or, conversely, that hospitalization
or nursing home residency can be thought of as having contributed an additional
47% of the cases once we accounted for malignant neoplasm. Institutionalization
plus trauma accounted for 62% of incident venous thromboembolism cases, while
institutionalization plus congestive heart failure accounted for 61% of cases
and institutionalization plus prior central venous catheter or pacemaker accounted
for 60% of cases. All 8 risk factors together accounted for 74% (95% CI, 70%-79%)
of all venous thromboembolism cases observed. Thus, if all 8 risk factors
could be eliminated, just over 25% of the venous thromboembolism cases in
the community would still be unexplained.
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Age-, sex-, event year–, main effects–, and interactions-adjusted
population attributable risk associated with the 5 most important independent
risk factors (institutionalization [hospitalization with or without surgery
or nursing home confinement], active malignant neoplasm [with or without chemotherapy],
trauma, congestive heart failure, and prior central venous catheter or pacemaker),
or all 8 independent risk factors for first lifetime definite venous thromboembolism,
among Olmsted County, Minnesota, residents during the 15-year period 1976
to 1990. Error bars represent 95% confidence intervals.
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COMMENT
Proper interpretation of population attributable risk, defined as the
percentage of all cases of a disease in a population that can be attributed
to a risk factor, requires the establishment of causality between the risk
factor and the disease. However, causality is a complex concept and raises
many questions that are not easily resolved. It is not easy to establish that
a factor "causes" a disease, and, after centuries of debate, there is little
consensus regarding the definitions of causality or how to establish it. This
fact notwithstanding, we believe that the elucidation of attributable risk
estimators, even when causality remains uncertain, is extremely useful in
focusing further research. Thus, it is logical that further research or even
intervention be planned around factors that alone or collectively are associated
with large attributable risk estimators rather than around those factors associated
with minimal attributable risk estimators.
Our analysis indicates that the incidence of venous thromboembolism
might be reduced by about 75% if prophylaxis were universally prescribed and
effective, and if other currently recognized risk factors could be modified
or avoided. Thus, hospitalization and nursing home residence (current or recent)
together accounted for almost 60% of all cases of venous thromboembolism disease
in the community. Of note, hospitalization for medical illness and hospitalization
for surgery accounted for almost equal proportions of venous thromboembolism
(22% and 24%, respectively), emphasizing the need to provide prophylaxis for
both of these risk groups. Only 9% of our hospitalized patients were receiving
anticoagulants at the time of venous thromboembolism onset, including 10%
of patients hospitalized with surgery and 7% of patients hospitalized for
medical illness.
Nursing home residence independently accounted for more than one tenth
of all cases of venous thromboembolism disease in the community. Nursing home
residents usually have not been considered for venous thromboembolism prophylaxis.
Moreover, these patients often have other conditions that place them at high
risk for anticoagulant-related complications, particularly bleeding. Consequently,
universal prophylaxis for such patients is unlikely to be cost-effective.
Additional studies are needed to identify risk factors for venous thromboembolism
among nursing home residents (independent of cancer, congestive heart failure,
or neurological disease with extremity paresis) such that prophylaxis can
be targeted to those patients at highest risk when appropriate.
Malignant neoplasm accounted for almost one fifth of all cases of venous
thromboembolism disease in the community. Among patients with cancer, malignant
neoplasms not requiring cytotoxic or immunosuppressive chemotherapy accounted
for almost twice the incidence of venous thromboembolism compared with cancers
requiring chemotherapy. Although we did not collect data on cancer type, breast
and prostate cancer commonly are treated with therapies other than cytotoxic
or immunosuppressive chemotherapy and may account for a substantial proportion
of venous thromboembolism due to malignant neoplasm. Additional studies are
needed to identify risk factors for venous thromboembolism among patients
with cancer.
Trauma, congestive heart failure, and placement of a central venous
catheter or transvenous pacemaker accounted for similar proportions of venous
thromboembolism in the community. The burden of disease accounted for by central
venous catheters (9%) is particularly noteworthy as a relatively recent risk
factor and emphasizes the need for additional studies addressing the safety
and efficacy of anticoagulant-based prophylaxis in this patient group. The
proportion of disease accounted for by neurological disease with extremity
paresis and prior superficial vein thrombosis also was similar.
About 25% of all cases of venous thromboembolism in the community could
not be accounted for by these risk factors. Only a small portion of this disease
could be attributed to other potential risk factors not identified in our
case-control study.6 For example, only 91 of
our 1244 female patients with incident venous thromboembolism had pregnancy
or the puerperium as a baseline characteristic, and only 173 were receiving
oral contraceptives (n = 103), hormone replacement therapy (n = 68), or both
(n = 2). Although we collected all available clinical data on coagulation
disorders, most patients and controls did not undergo laboratory testing for
these disorders. Moreover, the most common coagulation disorder (eg, activated
protein C resistance)17 had not been described
at the inception of our study.
A major strength of our study is that it is population-based. Therefore,
our study is completely representative of persons within Olmsted County who
met our criteria for a definite deep vein thrombosis or a definite pulmonary
embolism over the 15-year period 1976-1990. Over this study period, the population
of Olmsted County was approximately 98% white and of non-Hispanic ancestry.
Consequently, our results can only be generalized to similar populations.
In summary, currently recognized clinical risk factors account for about
75% of venous thromboembolism cases in the community, while about 25% remain
idiopathic. Appropriate prophylaxis should be provided for all patients at
risk, and, where possible, exposure to risk factors should be avoided or minimized.
However, of the patients with one or more of these risk factors, most do not
develop venous thromboembolism. Additional studies are needed to identify
characteristics that can stratify risk among these patient subsets and allow
prophylaxis to be tailored accordingly.
AUTHOR INFORMATION
Accepted for publication October 4, 2001.
This study was funded in part by grants HL 46974, HL 66216, and AR 30582
from the National Institutes of Health, US Public Health Service, Bethesda,
Md.
Corresponding author: John A. Heit, MD, Hematology Research, Stabile
660, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
From the Division of Cardiovascular Diseases and Section of Hematology
Research (Dr Heit) and the Division of Area General Internal Medicine (Drs
Silverstein and Mohr), Department of Internal Medicine, and the Divisions
of Biostatistics (Dr O'Fallon and Mss Petterson and Lohse) and Clinical Epidemiology
(Dr Melton), Department of Health Sciences Research, Mayo Clinic and Mayo
Foundation, Rochester, Minn.
REFERENCES
| |
1. Silverstein MD, Heit JA, Mohr DN, Petterson TM, O'Fallon WM, Melton III LJ. Trends in the incidence of deep vein thrombosis and pulmonary embolism:
a 25-year population-based study. Arch Intern Med. 1998;158:585-593.
FREE FULL TEXT
2. Heit JA, Silverstein MD, Mohr DN, Petterson TM, O'Fallon WM, Melton III LJ. Predictors of survival after deep vein thrombosis and pulmonary embolism:
a population-based cohort study. Arch Intern Med. 1999;159:445-453.
FREE FULL TEXT
3. Mohr DN, Silverstein MD, Heit JA, Petterson TM, O'Fallon WM, Melton III LJ. The venous stasis syndrome after deep venous thromboembolism or pulmonary
embolism: a population-based study. Mayo Clin Proc. 2000;75:1249-1256.
ISI
| PUBMED
4. Prandoni P, Lensing AW, Cogo A, et al. The long-term clinical course of acute deep venous thrombosis. Ann Intern Med. 1996;125:1-7.
FREE FULL TEXT
5. Bergqvist D, Jendteg S, Johansen L, Persson U, Ödegaard K. Cost of long-term complications of deep venous thrombosis of the lower
extremities: an analysis of a defined patient population in Sweden. Ann Intern Med. 1997;126:454-457.
FREE FULL TEXT
6. Heit JA, Silverstein MD, Mohr DN, Petterson TM, O'Fallon WM, Melton III LJ. Risk factors for deep vein thrombosis and pulmonary embolism: a population-based
case-control study. Arch Intern Med. 2000;160:809-815.
FREE FULL TEXT
7. Geerts WH, Heit JA, Clagett GP, et al. Prevention of venous thromboembolism. Chest. 2001;119(suppl):132S-175S.
8. Heit JA, Melton III LJ, Lohse CM, et al. Incidence of venous thromboembolism in hospitalized patients versus
community residents. Mayo Clin Proc. 2001;76:1102-1110.
ISI
| PUBMED
9. Madhok R, Lewallen DG, Wallrichs SL, Ilstrup DM, Kurland RL, Melton III LJ. Trends in the utilization of primary total hip arthroplasty, 1969 through
1990: a population-based study in Olmsted County, Minnesota. Mayo Clin Proc. 1993;68:11-18.
ISI
| PUBMED
10. Anderson FA Jr, Wheeler HB, Goldberg RJ, Hosmer DW, Forcier A, Patwardhan NA. Physician practices in the prevention of venous thromboembolism. Ann Intern Med. 1991;115:591-595.
11. Bratzler DW, Raskob GE, Murray CK, Bumpus LJ, Piatt DS. Underuse of venous thromboembolism prophylaxis for general surgery
patients in the community. Arch Intern Med. 1998;158:1909-1912.
FREE FULL TEXT
12. Melton III LJ. History of the Rochester Epidemiology Project. Mayo Clin Proc. 1996;71:266-274.
ISI
| PUBMED
13. Kurland LT, Molgaard CA. The patient record in epidemiology. Sci Am. 1981;245:54-63.
ISI
| PUBMED
14. Bruzzi P, Green SB, Byar DP, Brinton LA, Schairer C. Estimating the population attributable risk for multiple risk factors
using case-control data. Am J Epidemiol. 1985;122:904-914.
FREE FULL TEXT
15. Benichou J, Gail MH. Variance calculations and confidence intervals for estimates of the
attributable risk based on logistic models. Biometrics. 1990;46:991-1003.
FULL TEXT
|
ISI
| PUBMED
16. Kahn MJ, O'Fallon WM, Sicks JD. Generalized Population Attributable Risk Estimation. Rochester, Minn: Dept of Health Sciences Research, Mayo Clinic; April
1998. Technical Report Series, No. 54.
17. Koster T, Rosendaal FR, de Ronde H, et al. Venous thrombosis due to poor anticoagulant response to activated protein
C: Leiden Thrombophilia Study. Lancet. 1993;342:1503-1506.
FULL TEXT
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ISI
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