Structured Abstract
Please note: In 2003, the CTF updated its Grades of
Recommendations to include an "I Recommendation" for situations where
insufficient evidence exists to allow a recommendation to be made.
(Formerly, these situations were captured under a "C
Recommendation".) This change is not retroactive, and all
"C Recommendations" made prior to 2003 have not been
reevaluated in light of the new "I" recommendation grade. For a
discussion of these recommendation grades, please link to the 2003 article in
the Canadian Medical Association Journal here.
Screening for Abdominal Aortic Aneurysm
Prepared by Christopher Patterson, MD, FRCPC,
Professor and Head, Division of Geriatric Medicine, McMaster University,
Hamilton, Ontario
These recommendations were finalized by the Task Force in January 1994
Contents
Objective
To make recommendations for screening for abdominal aortic aneurysm (AAA),
(localized abnormal dilation of the aorta caused by atherosclerotic changes
in the arterial intima). AAA is defined as a dilation of the aorta ³
3 cm or 150% of the aortic diameter at the diaphragm (usually 2 cm in men
aged 65 to 74 y). This is an update of the 1991 Canadian Task Force Report.
Burden
of Suffering
Abdominal aortic aneurysm (AAA), a localized abnormal dilatation of the
aorta, is usually due to atherosclerotic changes affecting the arterial
intima. It is defined as a dilatation of the aorta greater than 3 cm or
150% of the aortic diameter at the diaphragm (usually 2 cm in men aged
65-74 years). In community surveys, the prevalence of AAA is reported to
be between less than 1% and 5.4%. The incidence of aneurysm has been estimated
at 52 and 499 per 100,000 per annum for men aged 55-64 years and over 80
years, respectively. Although AAA may remain asymptomatic for years, pressure
effects on adjacent structures, embolization of intramural thrombus, or
other vascular complaints such as intermittent claudication, may cause
indirect symptoms (e.g., back pain or abdominal throbbing). The characteristic
presentation of aortic rupture includes excruciating back pain, hypovolemic
shock and pulsatile abdominal mass. The classic triad is present in approximately
70% of cases reaching the hospital.
Options
Screening is either by physical examination; or abdominal ultrasound.
Outcomes
Sensitivity and specificity for both tests, mortality and cost of life-years
saved.
Evidence
MEDLINE was searched for 1980 to 1993 using the keywords aortic aneurysm,
aorta, abdominal, costs and cost analysis, decision making and mass screening.
Recommendations were graded as:
|
A
|
Good evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
B
|
Fair evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
C
|
Poor evidence regarding inclusion or exclusion of the condition
in a PHE, but recommendations may be made on other grounds. |
|
D
|
Fair evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
|
E
|
Good evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
Quality of evidence was rated according to 5 levels:
|
I
|
Evidence from at least 1 properly randomized controlled
trial (RCT). |
|
II-1
|
Evidence from well-designed controlled trials without randomization. |
|
II-2
|
Evidence from well-designed cohort or case-control analytic
studies, preferably from more than 1 centre or research group. |
|
II-3
|
Evidence from comparisons between times or places with
or without the intervention. Dramatic results in uncontrolled experiments
could also be included here. |
|
III
|
Opinions of respected authorities, based on clinical experience,
descriptive studies or reports of expert committees. |
Values
The 13-member Task Force of experts in family medicine, geriatric medicine,
pediatrics, psychiatry and epidemiology used an evidence-based method for
evaluating the effectiveness of preventive health care interventions. Recommendations
were not based on cost-effectiveness of options. Patient preferences were
not discussed.
Background papers providing critical appraisal of the evidence and tentative
recommendations prepared by the chapter author were pre-circulated to the
members. Evidence for this topic was presented and deliberated upon in
1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993.
Consensus was reached on final recommendations.
Benefits,
Harms, and Costs
When the presence prevalence of AAA is between 5% and 10%, physical examination
has a sensitivity of 22% to 50% and a specificity of 71% to 94%. Where
the prevalence of large AAA is high (e.g. in pre-operative vascular clinics),
the sensitivity is above 80%, with high specificity.; accuracy Accuracy
of physical examination depends on the skill of the examiner, the size
of the aneurysm, and habitus of the individual. Abdominal ultrasound, although
more expensive, has a sensitivity of almost 100%. Technical problems are
overestimation of the size of the AAA and inadequate visualization for
obese patients and those with excessive intestinal gas. Screening programs
generally have low compliance rates. Routine surgery for AAA has a mortality
rate of < 5% while surgery after rupture has a mortality rate of 50%
to 70%.or more. A small aneurysm gradually enlarges and the risk for rupture
increases with size. Risk factors for AAA are male gender, age > 60 years,
smoking, hypertension, claudication, evidence of other vascular diseases,
and a family history of AAA. Comorbidities affect survival after surgery.
Screening with abdominal palpation gives 20 life years at a cost of U.S.
$28 741/life-year; a single ultrasound screen gains 57 life-years at a
cost of $ 41 550/life-year; and repeat ultrasound screens gain 1 additional
life-year at a cost of $ 906 769.
Recommendations
Recommendation grade [A, B, C, D, E] and level of evidence
[I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations
in support of individual recommendations are identified in the guideline
text.
-
There is poor evidence to include or exclude abdominal
palpation for detection of AAA in
the PHE for asymptomatic adults [C, III].
-
There is poor evidence to include or excludeabdominal
ultrasound for detection of AAA
in the PHE for asymptomatic adults [C, II-2].
-
Screening may be considered for patients at high risk (men ³
60 years of age who smoke or have hypertension, claudication, evidence
of other vascular disease, or a family history of AAA). [C,
II-2].
Validation
This report was externally peer reviewed. This report was externally peer-reviewed.
No other organizations have made recommendations for screening for AAA.
Sponsors
The Canadian Task Force on Preventive Health Care
developed this guideline with funding from Health Canada.
Selected
References
Source Document
Other
-
Canadian Task Force on the Periodic Health Examination: The periodic health
examination, 1991 update: 5. Screening for abdominal aortic aneurysm. Can
Med Assoc J. 1991;145:783-9.
Link to Full Text of this
review
Link to Summary Table of Recommendations of this review
Link to Selected References list of this review
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