Screening for Abdominal Aortic Aneurysm: U.S. Preventive Services
This paper reviews the evidence for abdominal aortic aneurysm (AAA) screening and issues the United States Preventive Services Task Force (USPSTF) recommendations. The following are 11 key points from the recommendation statement:
1. AAA is defined as an abdominal aorta measuring 3.0 cm or larger. These are found in 3.9-7.2% of all men and 1.0-1.3% of all women ages 50+ years. Screening strategies are important because the vast majority of AAAs are asymptomatic until they rupture. However, once an AAA ruptures, the mortality is as high as 75-90%.
2. Four large population-based randomized controlled trials (RCTs) demonstrated benefit of one-time screening for AAA. These trials demonstrated benefit beginning 3 years after screening and persisting for up to 15 years after the one-time screening event. In addition, risk reduction for AAA rupture and emergency surgery persisted for up to 10-13 years following one-time screening.
• In the highest quality trials, the relative risk reduction in AAA-specific mortality after 13 years was 42-66%. AAA prevalence in the group receiving screening was approximately 5%, leading to an absolute risk reduction in death of 1.4 per 1,000 men.
3. AAAs are most prevalent in men who have ever smoked, occurring in 6-7% of this population. Screening trials have focused on these men, ages 65-75 years, to maximize the benefit of a one-time screening intervention.
• Men who have never smoked have a lower prevalence of AAA (approximately 2%), making the screening intervention less beneficial than in men who have ever smoked.
4. Only one RCT for AAA screening included women, but it failed to detect a difference in the rate of rupture, AAA-specific mortality, or all-cause mortality between the women who received screening and those who did not get screened. This trial was underpowered to detect differences in this population.
5. AAAs can be easily identified through a variety of imaging modalities, including computed tomography scanning, magnetic resonance imaging scanning, and ultrasound. Ultrasound has the benefit of easy access, no radiation, and low cost. Therefore, ultrasound is the recommended screening modality.
6. More than 90% of the AAAs identified through screening in the RCTs were below the 5.5 cm threshold for immediate repair. However, groups who received screening were twice as likely as those in the control group to undergo AAA surgery within 3-5 years, predominately driven by elective AAA repair procedures.
7. The risk of death from elective AAA surgery is quite low, and lower than that for death related to emergent AAA repair. However, increased detection through screening has the potential to induce harm in patients at low risk for rupture who may undergo elective AAA repair.
• Many patients who undergo AAA repair resulting from screening may have died from other causes before their AAA would have ruptured. In a historical study of 24,000 autopsies between 1952 and 1975, 75% of the cases where an AAA was found on autopsy, the cause of death was unrelated to AAA.
8. AAA repair can be performed via open surgical techniques or through endovascular techniques. Compared to men, women have a higher rate of AAA surgical mortality: 7% vs. 5% for open repair and 2% vs. 1% for endovascular repair.
9. The USPSTF gives a strong recommendation for a one-time AAA screen with ultrasound for men between 65-75 years of age who have ever smoked. They suggest moderate net benefit for screening in this population.
10. The USPSTF gives a moderate recommendation for a one-time AAA screen with ultrasound for men between 65-75 years of age who have never smoked. They suggest small net benefit for screening in this population.
• The American College of Cardiology and the American Heart Association recommend screening for men ages 60+ with a sibling or parent who had an AAA.
11. The USPSTS concludes that evidence is insufficient to recommend for AAA screening in women, regardless of smoking status.
Keywords: Esophageal Achalasia, Endovascular Procedures, Aortic Rupture, Risk Reduction Behavior, Numbers Needed To Treat, American Heart Association, Aortic Aneurysm, Abdominal, Aorta, Abdominal, Autopsy, Magnetic Resonance Imaging
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