The USPSTF found good evidence that screening for AAA and surgical repair of large AAAs (5.5 cm) in men age 65 to 75 years who have ever smoked (current and former smokers) leads to decreased AAA-specific mortality. There is good evidence that abdominal ultrasonography, performed in a setting with adequate quality assurance (that is, in an accredited facility with credentialed technologists), is an accurate screening test for AAA. There is also good evidence of important harms of screening and early treatment, including an increased number of surgeries with associated clinically significant morbidity and mortality, and short-term psychological harms. On the basis of the moderate magnitude of net benefit, the USPSTF concluded that the benefits of screening for AAA in men age 65 to 75 years who have ever smoked outweigh the harms. (See Appendix Table 2 for a description of the USPSTF classification of levels of evidence.)

The USPSTF makes no recommendation for or against screening for AAA in men age 65 to 75 years who have never smoked. This is a grade C recommendation.

The USPSTF found good evidence that screening for AAA in men age 65 to 75 years who have never smoked leads to decreased AAA-specific mortality. There is, however, a lower prevalence of large AAAs in men who have never smoked compared with men who have ever smoked; thus, the potential benefit from screening men who have never smoked is small. There is good evidence that screening and early treatment lead to important harms, including an increased number of surgeries with associated clinically significant morbidity and mortality, and short-term psychological harms. The USPSTF concluded that the balance between the benefits and harms of screening for AAA is too close to make a general recommendation in this population.

The USPSTF recommends against routine screening for AAA in women. This is a grade D recommendation.

Because of the low prevalence of large AAAs in women, the number of AAA-related deaths that can be prevented by screening this population is small. There is good evidence that screening and early treatment result in important harms, including an increased number of surgeries with associated morbidity and mortality, and psychological harms. The USPSTF concluded that the harms of screening women for AAA outweigh the benefits.

Clinical Considerations

The major risk factors for AAA include age (65 years), male sex, and a history of ever smoking (100 cigarettes in a person's lifetime). A first-degree family history of AAA requiring surgical repair also elevates a man's risk for AAA; this may also be true for women but the evidence is less certain. There is only a modest association between risk factors for atherosclerotic disease and AAA.

Screening for AAA would most benefit those who have a reasonably high probability of having an AAA that is large enough or will become large enough to benefit from surgery. In general, adults younger than age 65 years and adults of any age who have never smoked are at low risk for AAA and are not likely to benefit from screening. Among men age 65 to 74 years, an estimated 500 who have ever smoked—or 1783 who have never smoked—would need to be screened to prevent 1 AAA-related death in the next 5 years. As always, clinicians must individualize recommendations depending on a patient's risk and likelihood of benefit. For example, some clinicians may choose to discuss screening with male nonsmokers nearing age 65 who have a strong first-degree family history of AAA that required surgery.

The potential benefit of screening for AAA among women age 65 to 75 years is low because of the small number of AAA-related deaths in this population. The majority of deaths from AAA rupture occur in women age 80 years or older. Because there are many competing health risks at this age, any benefit of screening for AAA would be minimal. Individualization of care, however, is still required. For example, a clinician may choose to discuss screening in the unusual circumstance in which a healthy female smoker in her early 70s has a first-degree family history for AAA that required surgery.

Operative mortality for open surgical repair of an AAA is 4% to 5%, and nearly one third of patients undergoing this surgery have other important complications (for example, cardiac and pulmonary). In addition, men having this surgery are at increased risk for impotence.

Endovascular repair of AAAs (EVAR) is currently being used as an alternative to open surgical repair. Although recent studies have shown a short-term mortality and morbidity benefit of EVAR compared with open surgical repair, the long-term effectiveness of EVAR to reduce AAA rupture and mortality is unknown. The long-term harms of EVAR include late conversion to open repair and aneurysmal rupture. EVAR performed with older-generation devices is reported to have an annual rate of rupture of 1% and conversion to open surgical repair of 2%. The conversion to open surgical repair is associated with a perioperative mortality of about 24%. The long-term harms of newer-generation EVAR devices are yet to be reported.

For most men, age 75 years may be considered an upper age limit for screening. Patients cannot benefit from screening and subsequent surgery unless they have a reasonable life expectancy. The increased presence of comorbid conditions for people age 75 years and older decreases the likelihood that they will benefit from screening.

Ultrasonography has a sensitivity of 95% and specificity of nearly 100% when performed in a setting with adequate quality assurance. The absence of quality assurance is likely to lower test accuracy. Abdominal palpation has poor accuracy and is not an adequate screening test.

One-time screening to detect an AAA using ultrasonography is sufficient. There is negligible health benefit in rescreening those who have normal aortic diameter on initial screening.

Open surgical repair for an AAA of at least 5.5 cm leads to an estimated 43% reduction in AAA-specific mortality in older men who undergo screening. However, there is no current evidence that screening reduces all-cause mortality in this population.

In men with intermediate-sized AAAs (4.0 to 5.4 cm), periodic surveillance offers comparable mortality benefit to routine elective surgery with the benefit of fewer operations. Although there is no evidence to support the effectiveness of any intervention in those with small AAAs (3.0 to 3.9 cm), there are expert opinion–based recommendations in favor of periodic repeated ultrasonography for these patients.

Discussion

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By definition, an AAA is present when the infrarenal aortic diameter exceeds 3.0 cm (1). Large AAAs are associated with approximately 9000 deaths annually in the United States (2). The prevalence of AAAs found in population-based ultrasonography screening studies from various countries is about 4% to 9% in men and 1% in women (3-8). The prevalence of an AAA greater than 5.0 cm in men age 50 to 79 years is estimated to be 0.5% (9). Almost all deaths from ruptured AAAs occur in men older than age 65 years, most AAA-related deaths occur in men younger than age 80 years, and most AAA-related deaths in women occur in those older than age 80 years (10, 11).

The strongest risk factor for the rupture of an AAA is maximal aortic diameter (12, 13). The natural history of clinically apparent AAAs of 5.5 cm or more is difficult to determine, since most large aneurysms are surgically repaired. Results of 1 study showed that 1-year incidence rates of rupture were 9% for AAAs of 5.5 to 5.9 cm, 10% for AAAs of 6.0 to 6.9 cm, and 33% for AAAs of 7.0 cm or more (14). A rapid rate of aneurysm expansion exceeding 1.0 cm/y is commonly used in making decisions about the elective repair of AAAs less than 5.5 cm; however, the predictive value of expansion as an index of rupture risk is less clear (15).

The major risk factors for AAA include male sex, a history of ever smoking (defined in surveys as 100 cigarettes in a person's lifetime), and age 65 years or older. Other lesser risk factors include family history, coronary heart disease, claudication, hypercholesterolemia, hypertension, cerebrovascular disease, and increased height (16). Factors associated with decreased risk include female sex, diabetes mellitus, and black race.

Screening abdominal ultrasonography in asymptomatic individuals is an accurate test, with 95% sensitivity and near 100% specificity (17, 18). The USPSTF review identified 4 randomized, controlled trials (RCTs) of screening for AAA; these RCTs predominantly screened white men age 65 years and older (16, 18). A good-quality RCT of 67 800 white men age 65 to 74 years was conducted to evaluate screening for AAA (4). Screening was performed by ultrasonography and surgery in men with AAAs greater than 5.4 cm. The study showed that AAA-related mortality was reduced by an average of 42% (95% CI, 22% to 58%) in the screened population compared with the nonscreened population; the absolute reduction in AAA-specific mortality was 0.14% (0.33% in the nonscreened group and 0.19% in the screened group) (16).

A fair-quality RCT selected 15 775 white men and women age 65 to 80 years from family medical practices (19). This was the only one of the 4 RCTs that studied women. The prevalence of AAA in women was one sixth of that in men. The incidence of AAA rupture was the same in the screened and control groups of women. This trial lacked adequate power and reported a nonstatistically significant 41% reduction in AAA-related mortality in screened men and no reduction in AAA-related mortality in screened women. A fair-quality hospital-based RCT of 12 658 men age 65 to 73 years showed a 69% statistically significant reduction in AAA-specific mortality (20). Another RCT was population-based and included 38 704 men age 65 to 83 years. After 5 years of follow-up, 18 men in the group invited to be screened, and 25 in the control group, died of causes associated with AAA (odds ratio, 0.61 [95% CI, 0.04 to 1.11]). In a subgroup analysis, there was a statistically significant reduction in AAA-related mortality in men age 65 to 75 years, but not in older men (21). A meta-analysis of these trials showed a relative risk reduction of 43% in AAA-related deaths by screening for AAA, although there was no change in all-cause mortality (16, 18).

Death from AAA rupture after negative results on a single ultrasound scan at age 65 years is rare. Studies have shown that the incidence rate for new AAAs in a period of 10 years is low, ranging from 0% to 4%; none of the incident AAAs exceeded a diameter of 4.0 cm (11, 22-24). On the basis of these studies, negative results on a single ultrasound examination around the age of 65 years appears to virtually exclude the risk for future AAA rupture or death.

Two randomized trials showed no statistically significant mortality benefit from immediate surgical repair compared with frequent surveillance for intermediate-sized AAAs (4.0 to 5.4 cm) (25, 26). In addition, about 39% fewer AAA-related surgical repairs needed to be performed in the surveillance group.

Two randomized trials reported that the 30-day mortality rate for EVAR was significantly reduced compared with open surgical repair (about 1.5% vs. 4.5%, respectively) (27, 28). While there are short-term mortality and morbidity benefits of performing EVAR compared with open surgical repair, the magnitude of long-term potential harms is not well known. Long-term potential harms of EVAR may occur because of device failure, which could cause bleeding into the aneurysmal sac around the device or from retrograde flow into the aneurysmal sac through collateral blood vessels. These events may require late conversion to open repair or may lead to aneurysmal rupture. Studies of the EUROSTAR (EUROpean collaborators on Stent-graft Techniques for abdominal aortic Aneurysm Repair) registry report an annual rupture rate of 1% and conversion to open repair at an annual rate of 2%, with a 24% perioperative mortality rate for the conversion (29, 30).

Although open surgical repair remains the only proven intervention that leads to decreased AAA mortality in the long term, there are major harms associated with this procedure. One study showed in-hospital mortality rates for patients undergoing open repair to be 4.2% (31). The complication rate of elective surgery is about 32% and includes myocardial infarction, respiratory failure, renal failure, ischemic colitis, spinal cord ischemia, and prosthetic graft infections (16).

There is a short-term impact of AAA screening on quality-of-life measures. Those testing positive for AAA initially had more anxiety and lower physical and mental health scores (measured by the Short Form-36) than those testing negative. Those who underwent surgery, compared with those receiving continued surveillance, had slightly lower Short Form-36 scores but higher self-rated health scores 3 months after surgery. These negative psychological measures returned to normal levels within 12 months after screening or surgery (4).

The USPSTF review of 4 relevant cost-effectiveness studies of AAA yielded an estimated cost-effectiveness ratio of population-based AAA screening (compared with no screening) that is in the same range as that of other cost-effective preventive services (32).

The pathogenesis of AAA formation is complex and multifactorial; more studies are needed to clarify AAA's natural history of formation and expansion. A number of areas require further study, including the lack of a strong association between AAA and atherosclerotic disease; the prevalence and natural history of AAA in women; the efficacy of screening and treatment in nonwhite male populations; the efficacy and periodicity of surveillance of small AAAs (3.0 to 4.0 cm); and the long-term efficacy of EVAR as an alternative to open surgical repair, especially for AAAs less than 4.0 cm. There is also a need for a high-quality cost-effectiveness analysis of AAA screening conducted from the U.S. societal perspective.

Recommendations of Other Groups

The Society of Vascular Surgery and the Society for Vascular Medicine and Biology recommend AAA screening in all men age 60 to 85 years, women age 60 to 85 years with cardiovascular risk factors, and men and women age 50 years and older with a family history of AAA. These groups further recommend the following courses of action after screening: no further testing if aortic diameter is less than 3.0 cm, yearly ultrasonographic screening if aortic diameter is between 3.0 to 4.0 cm, ultrasonography every 6 months if aortic diameter is between 4.0 to 4.5 cm, and referral to a vascular specialist if aortic diameter is greater than 4.5 cm (33).

Appendix

Members of the U.S. Preventive Services Task Force are Ned Calonge, MD, MPH, Chair (Colorado Department of Public Health and Environment, Denver, Colorado); Janet D. Allan, PhD, RN, CS, Vice-Chair (University of Maryland, Baltimore, Baltimore, Maryland); Alfred O. Berg, MD, MPH (University of Washington, Seattle, Washington); Paul S. Frame, MD (Tri-County Family Medicine, Cohocton, and University of Rochester, Rochester, New York); Leon Gordis, MD, MPH, DrPH (Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland); Kimberly D. Gregory, MD, MPH (Cedars-Sinai Medical Center, Los Angeles, California); Russell Harris, MD, MPH (University of North Carolina School of Medicine, Chapel Hill, North Carolina); Mark S. Johnson, MD, MPH (University of Medicine and Dentistry of New Jersey–New Jersey Medical School, Newark, New Jersey); Jonathan D. Klein, MD, MPH (University of Rochester School of Medicine, Rochester, New York); Carol Loveland-Cherry, PhD, RN (University of Michigan School of Nursing, Ann Arbor, Michigan); Virginia A. Moyer, MD, MPH (University of Texas Health Science Center, Houston, Texas); Judith K. Ockene, PhD (University of Massachusetts Medical School, Worcester, Massachusetts); Diana B. Petitti, MD, MPH (Kaiser Permanente Southern California, Pasadena, California); Albert L. Siu, MD, MSPH (Mount Sinai Medical Center, New York, New York); Steven M. Teutsch, MD, MPH (Merck & Co., Inc., West Point, Pennsylvania); and Barbara P. Yawn, MD, MSc (Olmstead Research Center, Rochester, Minnesota).

This list includes members of the Task Force at the time this recommendation was finalized. For a list of current Task Force members, go to http://www.ahrq.gov/clinic/uspstfab.htm.