Screening for Abdominal Aortic Aneurysm: Recommendation Statement

Summary of the Recommendations The U.S. Preventive Services Task Force (USPSTF) recommends one-time screening for abdominal aortic aneurysm (AAA) by ultrasonography in men age 65 to 75 years who have ever smoked. This is a grade B recommendation. (See Appendix Table 1 for a description of the USPSTF classification of recommendations.) Appendix Table 1. U.S. Preventive Services Task Force Recommendations and Ratings 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.) Appendix Table 2. U.S. Preventive Services Task Force Grades for Strength of Overall 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 smokedor 1783 who have never smokedwould 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 opinionbased recommendations in favor of periodic repeated ultrasonography for these patients. Discussion 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 67800 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 15775 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 an