Screening for abdominal aortic aneurysms: single centre
randomised controlled trial
Jes S Lindholt, Svend Juul, Helge Fasting, Eskild W Henneberg
Objective To determine whether screening Danish men aged
65 or more for abdominal aortic aneurysms reduces mortality.
Design Single centre randomised controlled trial.
Setting All five hospitals in Viborg County, Denmark.
Participants All 12 639 men born during 1921-33 and living in
Viborg County. In 1994 we included men born 1921-9 (64-73
years). We also included men who became 65 during 1995-8.
Interventions Men were randomised to the intervention group
(screening by abdominal ultrasonography) or control group.
Participants with an abdominal aortic aneurysm > 5 cm were
referred for surgical evaluation, and those with smaller
aneurysms were offered annual scans.
Outcome measures Specific mortality due to abdominal aortic
aneurysm, overall mortality, and number of planned and
emergency operations for abdominal aortic aneurysms.
Results 4860 of 6333 men were screened (attendance rate
76.6%). 191 (4.0% of those screened) had abdominal aortic
aneurysms. The mean follow-up time was 52 months. The
screened group underwent 75% (95% confidence interval 51%
to 91%) fewer emergency operations than the control group.
Deaths due to abdominal aortic aneurysms occurred in nine
patients in the screened group and 27 in the control group. The
number needed to screen to save one life was 352. Specific
mortality was significantly reduced by 67% (29% to 84%).
Mortality due to non-abdominal aortic aneurysms was
non-significantly reduced by 8%. The benefits of screening may
increase with time.
Conclusion Mass screening for abdominal aortic aneurysms in
Danish men aged 65 or more reduces mortality.
Ruptured abdominal aortic aneurysm occurs in about 1-3% of
men aged 65 or more, 70-95% of whom die.1–4Mortality in peo-
ple undergoing elective surgery for abdominal aortic aneurysms
is only 5-7%,1but the condition seldom causes symptoms before
rupture. Consequently, screening for such aneurysms is worth
considering. A suitable and acceptable method of screening
populations seems available.1 5–11The psychological costs are
limited12 13because only 5% of people need rescanning every five
years.14The evidence base for treatment by size of aneurysm is
clear.15 16Abdominal aortic aneurysms may rupture during
surveillance, however, and patients still die after surgery for a
lesion that would never have ruptured if left untreated. Further-
more, surveillance decreases quality of life,12 17more than 10% of
patients have contraindications to surgery, and endovascular
treatment does not remove the risk of rupture after initial treat-
substantially reduces specific mortality. Consequently, we carried
out a randomised controlled trial to determine whether screen-
ing Danish men aged 64-73 for abdominal aortic aneurysms
Materials and methods
In 1994 we randomised all men born during 1921-9 who lived in
Viborg County, Denmark. To avoid delays between randomisa-
tion and screening, we randomised participants in blocks of
about 1000. In 1995-8 we randomised all those who became 65.
The mean age at randomisation was 67.7 years (range 64.3 to
We randomly assigned the men to either screening (6333
participants) or the control group (6306). Participants in the
screening group underwent abdominal ultrasonography at their
regional hospital. Non-responders were reinvited once. Scan-
ning (B mode) was carried out by a specially trained doctor and
nurse using a Phillips SDR 1550 device with linear 4 MHz trans-
ducer and calliper light pen. Participants were not required to
Baseline assessment and follow-up
We considered an abdominal aortic aneurysm to be present if
the infrarenal aortic diameter was ≥ 3 cm. Participants with
aneurysms ≥ 5 cm were referred to a vascular surgeon. The
remaining participants with aneurysms were offered annual
scans to check for expansion. They were referred for surgical
evaluation if the aneurysm had expanded to ≥ 5 cm. After five
years,men with an initial ectatic aorta (diameter 2.5-2.9 cm) were
The primary outcome measures were specific mortality due to
operations and indications for operations, and number of
ruptured aneurysms.Data on operations were obtained from the
We obtained data on deaths occurring from April 1994 to
December 1999 through the Danish civil register and causes of
death through the national register of causes of death. We
obtained the hospital records and autopsy records of patients
whose death certificates stated abdominal aortic aneurysm as the
primary or contributing cause of death. The information was
assessed by two vascular surgeons who were blinded to the ran-
domisation group and to each other’s evaluations. Each assessed
Cite this article as: BMJ, doi:10.1136/bmj.38369.620162.82 (published 9 March 2005)
BMJ Online First bmj.com
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the deaths to be certainly, possibly, or not caused by abdominal
aortic aneurysm. We considered deaths to be due to abdominal
aortic aneurysm when both assessors evaluated the death as cer-
tainly or possibly caused by such aneurysms.
We carried out analyses on an intention to screen basis from the
date of randomisation. Fisher’s exact test was used to compare
proportions. We used Cox proportional hazards regression to
compare specific mortality due to abdominal aortic aneurysm
and overall mortality. As the proportional hazards assumption
was not fulfilled,we decided to carry out separate analyses for the
periods before and after 1.5 years after randomisation.
We calculated the expected number of life years gained
within 5, 10, and 15 years for two hypothetical cohorts
representing screened participants and controls, each of 6333
men aged 67. In the cohort representing the controls, we
estimated the number of remaining life years from the life table
for Danish men in 1995 and 1996.In the cohort representing the
screened participants, we assumed the mortality for the period
1.5 to five years after randomisation to be reduced by the differ-
ence in specific mortality due to abdominal aortic aneurysm per
1000 years in the study (0.89, 95% confidence interval 0.40 to
1.37); before 1.5 years and after five years we assumed that the
mortality was unaffected by screening. We selected this interval
because evidence of a preventive effect was lacking until 1.5 years
after randomisation. The observed age specific mortality among
controls was close to Danish men in 1995 and 1996, but because
we observed the controls for less than six years we could not use
their data for projections beyond that. We carried out analyses
using SPSS 10.0 and Stata 8.0.
We randomised all 12 639 men aged 64-73 (mean age 67.7
years) living in Viborg County, Denmark (fig 1). They were
followed up for a mean of 52 months (range < 0-69 months).
The two groups were similar for duration of observation and age.
Overall, 4860 of 6333 participants allocated to the interven-
tion group were screened by abdominal ultrasonography
(attendance rate 76.6%, 95% confidence interval 75.6% to
77.7%). The anterior to posterior diameter of the aorta was suc-
cessfully measured in 4816 of the 4860 attenders (99.3%),and an
abdominal aortic aneurysm was detected in 191 (4.0%, 3.4% to
4.6%). Twenty four men (0.5%, 0.3% to 0.7%) with an aneurysm
≥ 5 cm were referred for surgery. During the five years after
screening, a further 22 men were referred for elective surgery
due to expansion of an aneurysm.
Operations and ruptures
The screened group underwent significantly fewer emergency
procedures than the control group (75.0%,50.9% to 91.3%;table
Overall,59 participants were operated on electively:48 in the
screened group and 11 in the control group. Of these, three (two
in the screened group) died within 30 days postoperatively
(5.1%). A fourth died 2.5 months postoperatively due to compli-
cations. Of those referred for surgery after screening, two died
aneurysm (surgery had to be postponed because of acute
myocardial infarction) and the other due to ruptured iliac aneu-
rysms. Furthermore, three participants with abdominal aortic
aneurysms in the screened group who were recommended for
surgery died of ruptured aneurysm; one initially had contraindi-
ruptured abdominal aortic
cations for surgery, one refused surgery, and one did not attend
Sixteen ofthe37 patients
underwent surgery (43.2%), 10 of whom died (62.5%). Overall,
the case fatality due to ruptured abdominal aortic aneurysm was
81.1% (64.8% to 92.0%), and the incidence of recognised
ruptured aneurysms in the control group was 1.07 per 1000
Mortality and survival
Nine participants in the screened group died from abdominal
aortic aneurysm compared with 27 in the control group (hazard
ratio 0.33, 0.16 to 0.71; fig 2). During the 18 months after
randomisation, the two groups showed similar mortality due to
abdominal aortic aneurysm (0.77, 0.29 to 2.07), but thereafter
mortality was lower in the screened group (0.11, 0.03 to 0.48).
In the screened group, all cause mortality was insignificantly
decreased (hazard ratio 0.92, 0.84 to 1.00; fig 3) and mortality
from causes other than abdominal aortic aneurysm was also
insignificantly decreased (0.92, 0.85 to 1.02).
The number of life years gained by offering 6333 men
screening was 32 (14 to 49) during the first five years (table 2). If
the prediction was extended to 10 and 15 years, the number of
life years gained was 107 (48 to 164) and 158 (71 to 244),respec-
Total mortality among non-attenders for screening was
significantly higher than that among those who did attend for
screening (hazard ratio 1.98, 1.73 to 2.26; fig 4).
Screening Danish men aged 64-73 for abdominal aortic
aneurysm reduced the need for emergency operations by 75%
and reduced specific mortality due to such aneurysms by 67%.
Thirty two life years were also gained during the five years after
screening.Life years gained could be expected to increase to 107
and 158 after 10 and 15 years, respectively. The number needed
Assessed for eligibility and randomised
Men aged 64-73 living in Viborg County (n=12 639)
no screening (n=6306)
Analysed on intention to treat
Deaths due to abdominal aortic
Analysed on intention to treat
Deaths due to abdominal aortic
Did not attend
Deaths due to
Deaths due to
Flow of participants through trial
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to screen to save one life was 352—an acceptable number when
compared with other types of screening.20
Our study groups had similar age distributions and average
times at risk.Our analysis was carried out according to the inten-
tion to screen principle, and we have no reason to suspect
It is possible that some deaths may have been misclassified as
due to abdominal aortic aneurysm, as autopsy was carried out in
only 6% of the participants. However, 43% of the patients with
ruptured aneurysm underwent surgery, providing enough data
for evaluation.Furthermore,the two vascular surgeons disagreed
on only three cases of death from hospital and autopsy reports.
The assessors were blinded to group allocation, and therefore
classification bias seems unlikely.
Deaths outside hospital may, however, have been misclassi-
fied; sudden death of a man with a known small abdominal aor-
tic aneurysm might risk misclassification as due to the aneurysm.
Cases with rupture of an unknown aneurysm risk being misclas-
sified as cardiac disease because of the high prevalence of coex-
isting cardiac morbidity. Both types of misclassification would
lead to an underestimation of the benefits of screening for
abdominal aortic aneurysm. This could partly explain why total
mortality in our study was close to being significantly reduced by
screening (see fig 2).
Another explanation could be that discussions about risk
factors during screening may have led to some participants
aneurysms were advised to stop smoking, and patients with sub-
standard management of high blood pressure were advised to
consult their doctor. No drugs or vitamin supplements were
given. Another explanation could be that the screened group
were favoured by randomisation by coincidence.
Nevertheless, the decrease in mortality due to such
aneurysms seems to compare well with our earlier results on
hospital deaths due to abdominal aortic aneurysms, when the
diagnosis was certain.21
After 3-5 years, the 162 survivors with an aorta diameter initially
sized at 25-29 mm were offered rescreening together with a ran-
dom sample of 275 survivors with an aorta initially sized at less
Table 1 Relative risks associated with screening Danish men aged 64-73 for abdominal aortic aneurysms
No of all operations
No of elective operations
No of emergency operations
No of ruptured aneurysms
No of deaths due to abdominal aortic aneurysm
Total No (%) of deaths
Screened group (n=6333)
Control group (n=6306)
Relative risk (95% CI)
1.70 (1.09 to 2.65)
4.35 (2.26 to 8.36)
0.25 (0.09 to 0.66)
0.27 (0.13 to 0.60)
0.33 (0.16 to 0.71)
0.92 (0.85 to 1.00)
Cumulated mortality per 1000
Danish men aged 64-73 years. Difference between screened and control groups
is P=0.003 (log rank test)
Kaplan-Meier estimates of mortality due to abdominal aortic aneurysm in
Cumulated total mortality per 1000
screened for abdominal aortic aneurysm and controls. Difference between
screened and control groups is P=0.053 (log rank test)
Kaplan-Meier estimates of total mortality in Danish men aged 64-73 years
Table 2 Expected life years gained by inviting 6333 Danish men aged 64-73
to be screened for abdominal aortic aneurysm
Period (years) after
Expected life years remaining
Expected life years gained
32 (14 to 49)
107 (48 to 164)
158 (71 to 244)
Cumulated total mortality per 1000
non-attenders for screening for abdominal aortic aneurysm. Difference is P<0.001
(log rank test)
Kaplan-Meier estimates of total mortality among attenders and
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than 25 mm. More than 80% attended for rescreening. None of
the controls had developed abdominal aortic aneurysms,
whereas 28% of those with an initially sized aorta of 25-29 mm
(range 30-48 mm) developed an aneurysm, with annual
expansion rates varying from 1.0 to 4.7 mm.14Three participants
were later referred for surgical evaluation. Thus, rescreening
patients with an aortic diameter of less than 25 mm seems
unwarranted, whereas patients with preaneurysms of 25-29 mm
diameter should be rescreened after five years.
We observed no deaths due to abdominal aortic aneurysm in the
screened group after 28 months (see fig 2). The number of elec-
tive procedures decreased rapidly after the first two years, and
therefore attenders were at low risk of deaths due to such
surgery.Four deaths due to abdominal aortic aneurysm occurred
significant and could be coincidental. Alternatively, selection
could be an explanation. We know from our previous studies on
this population, that those with diseases related to abdominal
aortic aneurysms attend screening more often than those
without,10 11so the prevalence of such aneurysms among
non-attenders could be expected to be lower than among
attenders. However, the lower frequency of diseases related to
abdominal aortic aneurysm among non-attenders was not asso-
ciated with better survival (see fig 4).
Our main results are limited to a relatively short observation
period.This is a conservative way to interpret the results,because
benefits are expected to increase with time. We estimated the
future benefits in terms of life years gained in 15 years.The main
assumptions behind the estimates were conservative: that
mortality not due to abdominal aortic aneurysm is unaffected by
screening and that screening has a net effect on mortality due to
abdominal aortic aneurysm only between 1.5 and five years after
screening, with difference in mortality due to such aneurysms
per 1000 years of 0.89 (0.40 to 1.37), as observed in the present
study. After five years, mortality due to abdominal aortic
aneurysm was assumed to be unaffected by screening.
This is probably an underestimation of the benefits, since the
incidence of ruptured abdominal aortic aneurysms increases
with age,1although the frequency of non-compliance among
patients with a conservatively treated aneurysm and those unfit
for surgery will probably also increase with age.
In the UK multicentre aneurysm screening study,13 22the
relative risk reduction was 42% (95% confidence interval 22% to
58%). Although lower than in our study, this value is not signifi-
cantly different from the 67% we observed.
In Western Australia,23a randomised trial among men aged
65-83 showed an insignificant relative risk of death due to
abdominal aortic aneurysm in the intervention group of 0.61
(95% confidence interval 0.33 to 1.11), but among the men aged
65-74 who were originally intended as participants the relative
risk was significant (0.19, 0.04 to 0.89). The findings from that
study are thus consistent with the UK multicentre study and our
findings that screening reduces mortality due to abdominal aor-
tic aneurysm. Further studies must analyse whether screening is
cost effective in Denmark and Western Australia.
however, was not
We thank vascular surgeons Jes Sandermann and Franz von Jessen for their
independent review of classification of cause of death in the autopsy and
hospital reports, and Anette Sahlholdt, Sten Vammen, Henriette Lindholt,
and Jette Støvring for assistance with data collection.
Contributors: All authors planned the project, revised the article, and
approved the final manuscript. JSL collected the data. JSL and SJ are guar-
antors.They accept full responsibility for the work and conduct of the study,
had access to the data, carried out the analyses, and controlled the decision
Funding: Health department of Viborg County, Danish Heart Foundation,
Danish National Council of Health Research, Foundation of Research in
Western Denmark, and Foundation of Rosa and Asta Jensen.
Competing interests: None declared.
Ethical approval: The trial was approved by the local scientific ethics com-
mittee of the counties of Viborg and Nordjylland.
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old men for abdominal aortic aneurysms in the county of Viborg, Denmark. J Med
What is already known on this topic
Ultrasonography is a safe and reliable screening method for
abdominal aortic aneurysms
The evidence base for treatment by size of aneurysm is
Randomised screening trials have shown a significant
reduction in specific mortality due to abdominal aortic
What this study adds
Mass screening for abdominal aortic aneurysm in Danish
men aged 64-73 reduced specific mortality by 67%
The number needed to screen to save one life was 352
page 4 of 5
BMJ Online First bmj.com
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for abdominal aortic aneurysms.Results from a randomised population screening trial.
Eur J Vasc Endovasc Surg 2002;23:55-60.
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tre aneurysm screening study (MASS) into the effect of abdominal aortic aneurysm
screening on mortality in men: a randomised controlled trial. Lancet 2002;360:1531-9.
23 Norman PE, Jamrozik K, Lawrence-Brown MM, Le MTQ, Spencer CA, Tuohy RJ, et al.
Population based randomised controlled trial on impact of screening on mortality
from abdominal aortic aneurysm. BMJ 2004;329:1259-62.
(Accepted 14 January 2005)
Vascular Research Unit, Department of Vascular Surgery, Sygehus Viborg,
DK-8800 Viborg, Denmark
Jes S Lindholt senior lecturer
Helge Fasting consultant
Eskild W Henneberg consultant
Department of Epidemiology, Institute of Public Health, University of Aarhus,
DK-8000 Aarhus C, Denmark
Svend Juul senior lecturer
Correspondence to: J S Lindholt firstname.lastname@example.org
BMJ Online First bmj.com
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