Note: This draft Recommendation Statement is not the final recommendation of the U.S. Preventive Services Task Force. This draft is distributed solely for the purpose of pre-release review. It has not been disseminated otherwise by the USPSTF. It does not represent and should not be interpreted to represent a USPSTF determination or policy.
This draft Recommendation Statement is based on an evidence review that was published on January 28, 2014 (available at http://www.uspreventiveservicestaskforce.org/uspstf14/abdoman/abdomanart.htm).
The USPSTF makes recommendations about the effectiveness of specific preventive care services for patients without related signs or symptoms.
It bases its recommendations on the evidence of both the benefits and harms of the service, and an assessment of the balance. The USPSTF does not consider the costs of providing a service in this assessment.
The USPSTF recognizes that clinical decisions involve more considerations than evidence alone. Clinicians should understand the evidence but individualize decisionmaking to the specific patient or situation. Similarly, the USPSTF notes that policy and coverage decisions involve considerations in addition to the evidence of clinical benefits and harms.
This draft Recommendation Statement is available for comment from January 28 until February 24, 2014 at 5:00 PM ET. You may wish to read the entire Recommendation Statement before you comment. A fact sheet that explains the draft recommendations in plain language is available here.
Screening for Abdominal Aortic Aneurysm: U.S. Preventive Services Task Force Recommendation Statement
Summary of Recommendations and Evidence
The U.S. Preventive Services Task Force (USPSTF) recommends one-time screening for abdominal aortic aneurysm (AAA) by ultrasonography in men ages 65 to 75 years who have ever smoked.
This is a B recommendation.
The USPSTF recommends that clinicians selectively offer screening for AAA in men ages 65 to 75 years who have never smoked rather than routinely screening all men in this group. Existing evidence indicates that the net benefit of screening all men ages 65 to 75 years who have never smoked is small. In determining whether this service is appropriate in individual cases, patients and clinicians should consider the balance of benefits and harms on the basis of evidence relevant to the patient's medical history, family history, other risk factors, and personal values.
The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for AAA in women ages 65 to 75 years who have ever smoked.
The USPSTF recommends against routine screening for AAA in women who have never smoked.
This is a D recommendation.
These recommendations apply to asymptomatic adults age 50 years and older.
AAA is typically defined as an aortic diameter of 3.0 cm or larger. Population-based studies in adults older than age 50 years have found that the prevalence of AAA is between 3.9% and 7.2% in men and 1.0% and 1.3% in women (1, 2). Considering potential screening strategies for AAA is important because most AAAs are asymptomatic until the time of rupture, and although the risk for rupture varies greatly by aneurysm size, the associated risk for death is as high as 75% to 90% with rupture (1, 2).
There is adequate evidence that ultrasonography is a safe and accurate screening test for AAA.
Benefits of Detection and Early Treatment
Men Ages 65 to 75 Years Who Have Ever Smoked
Four large population-based, randomized, controlled trials (RCTs) demonstrate that invitation to one-time AAA screening is associated with a reduction in AAA-specific mortality in men beginning 3 years after testing; this benefit persists up to 15 years (1, 2). In the two highest-quality trials, there was a 42% to 66% relative reduction in AAA-specific mortality after 13 years (3, 4). Risk for AAA rupture and emergent surgery are also reduced at up to 10 to 13 years (1, 2). AAAs are most prevalent in men who have ever smoked, occurring in about 6% to 7% of this population (5, 6). This increases the importance of screening in this population, as it maximizes the absolute benefit that could potentially be achieved (i.e., it improves the likelihood that an individual in this group will be helped by screening). There is convincing evidence that one-time screening for AAA with ultrasonography results in a moderate benefit in men ages 65 to 75 years who have ever smoked.
Men Ages 65 to 75 Years Who Have Never Smoked
Despite reductions in AAA-specific death, rupture, and emergent surgery seen with screening in men overall, the much lower prevalence of disease among men who have never smoked (about 2%) (5) substantially reduces the absolute benefit that could potentially be achieved (i.e., it greatly lowers the probability that an individual in this group will benefit from screening). There is adequate evidence that one-time screening for AAA with ultrasonography results in a small benefit in men ages 65 to 75 years who have never smoked.
Women Ages 65 to 75 Years Who Have Ever Smoked
A single RCT of screening for AAA included women in its study population (7). The trial detected no difference in AAA rupture rate, AAA-specific mortality, or all-cause mortality between women invited for screening and the control group (8). However, the trial was ultimately underpowered to detect differences in health outcomes by sex, and as such, the results do not rule out the possibility of a small benefit of screening in this population. Women age 70 years who have ever smoked have a relatively low prevalence of AAA (approximately 0.8% overall and about 2% for current smokers) (9). There is inadequate evidence to conclude whether one-time screening for AAA with ultrasonography produces any benefit in women ages 65 to 75 years who have ever smoked.
Women Who Have Never Smoked
Given the extremely low prevalence of AAA in women who have never smoked—0.03% to 0.6% of women ages 50 to 79 years (5, 9)—coupled with the available evidence showing no apparent benefit of screening for AAA in women (8), the USPSTF concludes there is adequate evidence that the absolute benefits of one-time screening for AAA with ultrasonography in women who have never smoked can effectively be bounded near zero.
Harms of Detection and Early Treatment
In the available screening trials, invitation to screening was associated with approximately twice the risk for any AAA surgery within 3 to 5 years compared with the control group, which was predominantly driven by an increase in elective surgeries. More than 90% of AAAs identified by screening were below the 5.5-cm threshold for immediate repair, leading to a requirement for long-term (potentially lifelong) surveillance (1, 2). One study reported that women had a higher risk for dying from AAA surgery than men; for open repair, death rates were about 7% versus 5%, respectively, and for endovascular repair, 2% versus 1% (10). There is limited and conflicting evidence about the effect of AAA screening on quality of life or psychological status (e.g., anxiety) (1, 2).
There is convincing evidence that the harms associated with one-time screening for AAA with ultrasonography are at least small in all populations, and potentially higher in women due to their higher risk for operative mortality.
The USPSTF concludes with high certainty that screening for AAA with ultrasonography in men ages 65 to 75 years who have ever smoked has a moderate net benefit.
The USPSTF concludes with moderate certainty that screening for AAA with ultrasonography in men ages 65 to 75 years who have never smoked has a small net benefit.
The USPSTF concludes that the evidence is insufficient to determine the balance of benefits and harms of screening for AAA in women ages 65 to 75 years who have ever smoked.
The USPSTF concludes with moderate certainty that the harms of screening for AAA outweigh any potential benefits in women who have never smoked.
Patient Population Under Consideration
This recommendation applies to asymptomatic adults age 50 years and older.
Assessment of Risk
Screening in Men Ages 65 to 75 Years Who Have Never Smoked
Despite the demonstrated benefits of screening for AAA in men overall, the much lower prevalence of disease in male never-smokers than in male ever-smokers suggests that clinicians should consider the patient's risk factors as well as the potential for causing harm when making the decision whether to screen, instead of routinely offering screening to all men who have never smoked. Important risk factors that increase risk for developing an AAA include older age and a first-degree relative with AAA; other risk factors include a history of other vascular aneurysms, coronary artery disease, cerebrovascular disease, atherosclerosis, hypercholesterolemia, obesity, and hypertension. African American race, Hispanic ethnicity, and diabetes are associated with reduced risk for developing an AAA (5, 11, 12).
Suggestions for Practice Regarding the I Statement
Screening in Women Ages 65 to 75 Years Who Have Ever Smoked
Potential preventable burden. A screening study in 70-year-old Swedish women found that the prevalence of AAA in female ever-smokers was quite low, at 0.8%, although it increased to 2% for current smokers (9). An individual patient data meta-analysis found that women have a higher risk than men for AAA rupture at the same diameter (hazard ratio [HR], 3.76 [95% CI, 2.58 to 5.47]) (13). However, AAA-associated deaths occur at an older age in women (at a time of increased competing causes of death and a declining benefit-to-risk ratio for operative interventions), with 70% of deaths occurring after age 80 years compared with fewer than 50% in men (1, 2). In the only screening RCT that included women, the majority of screen-detected AAAs in women were small (3.0 to 3.9 cm), and AAA-specific mortality was very low in both screened and unscreened women (<0.2%) after 10 years (8).
Potential harms. Four RCTs (primarily conducted in men) showed that screening for AAA doubled the rate of AAA-associated surgeries compared with the control groups, which was largely driven by an increase in elective operations. The vast majority of screen-detected AAAs were below the 5.5-cm threshold for immediate repair; this finding generally results in a requirement for long-term or lifelong surveillance. Most screening trials reported an associated decrease in emergent AAA repairs and a reduced 30-day emergency surgery death rate among populations invited to screening, although mortality associated with elective surgery was not reduced (1, 2). AAA-associated operative mortality is higher in women than in men (7% vs. 5% for open repair and 2% vs. 1% for endovascular repair, respectively) (10).
Costs. In addition to the cost of the screening ultrasound itself (approximately $100) (14.), there is also the potential associated cost of elective surgery to repair a screen-detected AAA (estimated range, $37,000 to $43,000) (15). There are also potential opportunity costs, as screening may take the place of other preventive activities that may be of greater benefit to the individual.
Current practice. Screening for AAA is provided as part of the “welcome to Medicare visit” for women who have a family history of AAA (16), but the evidence is insufficient to accurately characterize current clinician practice patterns related to AAA screening in women.
Ultrasonography was the primary modality in the available AAA screening trials, and is widely accepted as the standard approach for AAA screening by primary care physicians and vascular surgeons. Screening with ultrasonography is noninvasive, is easy to perform, and has high sensitivity (94% to 100%) and specificity (98% to 100%) for detecting AAA (1, 2). In addition, it has demonstrated high rates of reproducibility, avoids radiation exposure, and is relatively low in cost.
There is adequate evidence for one-time screening in men who have ever smoked. All the population-based randomized trials of AAA screening employed a one-time screening approach, and several fair- to good-quality prospective cohort studies show that over 5 to 12 years, AAA-associated mortality is low (0% to 2.4%) in men with an initially normal ultrasound (1, 2).
In the available screening trials, the observed AAA-related mortality benefit was achieved by immediate referral of patients with large AAA (≥5.5 cm) for open surgery, coupled with conservative management for smaller aneurysms (3.0 to 5.4 cm) via repeat ultrasound every 3 to 12 months. Surgical referral of smaller AAA was reserved for rapid growth (>1.0 cm per year) or reaching a threshold of 5.5 cm or larger on repeat ultrasound (1, 2).
Although early open surgery for the treatment of smaller AAA reduces the risk for rupture compared with surveillance, it does not reduce AAA-specific or all-cause mortality (17, 18). Endovascular repair (EVAR) is an alternative to open surgery. As with open surgery, randomized trials evaluating early EVAR compared with surveillance for the treatment of smaller AAA do not show a difference in all-cause or AAA-related mortality. Unlike early open surgery, early EVAR does not reduce the incidence of AAA rupture (19, 20).
Pharmacotherapy has been proposed to slow the growth of smaller AAA. Short-term treatment with antibiotics or beta-blockers does not appear to reduce AAA growth, and the trials were underpowered to draw conclusions about effects on health outcomes (1, 2).
Research Needs and Gaps
Several risk scoring tools have been developed and, if prospectively validated, could be used to identify patients most likely to benefit from screening. Thus, validation studies of these risk scoring tools should be prioritized. Because of the importance of family history as a risk factor, the role of genetic markers of AAA development should be explored.
While there is evidence that women who smoke are at increased risk for AAA compared with their nonsmoking counterparts, there is insufficient evidence that screening confers a net benefit. Appropriately powered RCTs as well as high-quality modeling studies should be done to determine whether screening is beneficial in women who smoke. The same is true for persons with a family history of AAA and those with combinations of risk factors.
There is a need to further explore alternative strategies to reduce AAA growth, such as antibiotics, statins, or other novel pharmacologic agents. Interventions to address modifiable risk factors (particularly smoking) may be worth considering. Effective smoking cessation strategies may improve the care of patients with small AAA. Seven ongoing RCTs are evaluating pharmacotherapeutic effects on small AAA; however, the outcome in most trials is aneurysmal growth and they are underpowered to detect changes in health outcomes. Appropriately powered studies that can assess health outcomes should be conducted to determine if such therapeutic treatments are viable options in preventing mortality.
One screening RCT, the Viborg Vascular (VIVA) trial, is currently evaluating the effectiveness of combined screening for AAA, peripheral artery disease, and hypertension in 50,000 men ages 65 to 74 years; results are not expected until after 2018. Participants who screen positive for AAA or peripheral artery disease are provided advice on exercise, low-fat diet, and smoking cessation and medical management with statins and aspirin. They receive annual surveillance for AAA and peripheral artery disease, and those with an AAA measuring 5.0 cm or larger are referred for surgery. Followup will occur at 3.5, 10, and 15 years for the primary outcome of all-cause mortality. Secondary outcomes include cardiovascular mortality, AAA-specific mortality, AAA prevalence and progression, health-related quality of life, and cost-effectiveness. This study may also provide evidence as to whether the presence of screen-detected AAA can be used as a marker and improve outcomes for other cardiovascular diseases (21).
Burden of Disease
AAA, defined as an aortic diameter of 3.0 cm or larger, is estimated to affect between 3.9% and 7.2% of men and 1.0% and 1.3% of women age 50 years and older. Several recent studies from population-based screening programs in men age 65 years and older have reported a declining AAA prevalence over the past two decades in the United Kingdom, New Zealand, and Sweden (overall population estimates range from 1.5% to 1.7%) (1, 2). One recent study in 70-year-old women in Sweden reported a similar decline in overall AAA prevalence (to approximately 0.5%) (9). This may be due to reductions in the rate of smoking and improvements in the treatment of hypertension and hyperlipidemia in these populations. However, the prevalence of AAA in male and female smokers does not appear to have declined.
The primary risk associated with AAA is rupture, which may occur suddenly, without symptoms, and is often fatal. However, the risk for AAA rupture varies substantially by the size of the aneurysm. AAAs with a diameter between 3.0 and 3.9 cm have an essentially 0% annual rupture risk, and those with a diameter between 4.0 and 4.9 cm have a 1% annual rupture risk; AAAs with a diameter between 5.0 and 5.99 cm have an 11% annual rupture risk (1, 2).
An estimated 59% to 83% of patients with a rupture die before hospitalization; operative mortality (in-hospital or 30-day) is approximately 40%. Thus, at most, 10% to 25% of individuals with a ruptured AAA survive to hospital discharge. Almost all deaths from ruptured AAA occur after age 65 years, and in women, the majority of deaths occur after age 80 years (1, 2).
Scope of Review
The USPSTF commissioned a systematic review to update its 2005 recommendation on AAA screening. The review assessed the evidence on the benefits and harms of AAA screening as well as strategies for managing small (i.e., 3.0 to 5.4 cm) screen-detected AAA.
Accuracy of Screening Tests
Primary care feasible or referable screening tests for AAA include ultrasonography, computed tomography (CT), and physical examination. The performance characteristics of these screening modalities were not systematically reviewed for this updated recommendation.
Ultrasonography is noninvasive; is easy to perform; avoids radiation exposure; has high sensitivity (94% to 100%), specificity (98% to 100%), and rates of reproducibility for detecting AAA; and is low in cost. Therefore, it is the primary technology used to screen for AAA (1, 2).
CT has relatively high sensitivity and specificity (90% and 91%, respectively) for detecting AAA, but it exposes patients to radiation, and the size of the aneurysms detected by CT are generally 2 mm larger than that measured by ultrasonography. Physical examination has far lower sensitivity (estimated range, 39% to 68%) and specificity (75%) than ultrasonography or CT (1, 2).
Effectiveness of Screening and Treatment
Four large population-based RCTs that predominantly enrolled men age 65 years and older examined the effectiveness of one-time screening for AAA: the good-quality Multicentre Aneurysm Screening Study (MASS) (n=67,800) (22); the good-quality Viborg County, Denmark screening trial (n=12,639) (23); the fair-quality Chichester, United Kingdom screening trial (n=15,775) (7); and the fair-quality Western Australia screening trial (n=41,000) (24). Reported mean (or median) ages ranged from 67.7 to 72.7 years; the oldest study participants were age 80 years (1, 2).
Men. AAA prevalence in male screening attendees ranged from 4.0% to 7.7% across the studies. The majority of screen-detected AAAs were small; only 0.4% to 0.6% of screened participants had an AAA measuring 5.0 or 5.5 cm or larger (1, 2).
AAA-related mortality. MASS and the Viborg trial each found a statistically significant reduction in AAA-related mortality in the group invited to screening compared with the control group between 4 and 13 years after screening (13-year HR, 0.58 [95% CI, 0.49 to 0.69] and 0.34 [95% CI, 0.20 to 0.57], respectively) (3, 4). The Western Australia and Chichester trials also had results favoring the screening group, but they were not statistically significant (24, 25).
All-cause mortality. None of the individual trials showed a statistically significant benefit to AAA screening for all-cause mortality at up to 15 years of followup. Pooled analysis of all available trials using a prespecified random-effects model also demonstrated no effect on all-cause mortality (risk ratio [RR], 0.98 [95% CI, 0.97 to 1.00]); sensitivity analysis using a profile likelihood estimation method yielded identical results. Sensitivity analysis using odds ratios (ORs) and a fixed-effects model found a statistically significant result at the longest time period (OR, 0.973 [95% CI, 0.950 to 0.997]) (1, 2). A lack of an all-cause mortality benefit is not entirely unexpected, as overall, across the trials, less than 3% of participant deaths were attributable to AAA.
AAA rupture. Invitation to screening was associated with a statistically significant reduced AAA rupture rate in MASS (HR, 0.57 [95% CI, 0.49 to 0.66]) and the Viborg trial (HR, 0.44 [95% CI, 0.24 to 0.79]) at 13 years of followup (3, 4). The Chichester trial found no statistically significant reduction in rupture rate at 15 years, although the point estimate was in the direction of benefit (HR, 0.88 [95% CI, 0.61 to 1.26]) (25). The Western Australia trial found no statistically significant difference at a median followup of 3.6 years (33 vs. 38 ruptures in the intervention and control groups, respectively) (24).
Emergency surgery. The rate of emergent AAA repair for rupture in the screened population was approximately halved after 13 years in MASS (3). In the Viborg trial, acute operations were reduced at up to 15 years, although the result was not statistically significant after the 10-year followup (HR, 0.32 [95% CI, 0.17 to 0.60] and 0.50 [95% CI, 0.15 to 1.65] at 10 and 15 years, respectively) (4, 26). The Chichester and Western Australia trials found no differences in the rate of emergency surgeries (24, 25).
Older men. Two of the population-based screening trials analyzed AAA-associated mortality by age. The Viborg trial found similar AAA-related mortality risk reduction with screening in men ages 64 to 65 years and men ages 66 to 73 years (4). The Western Australia trial found no difference in AAA-associated mortality with screening between participants ages 65 to 74 years and those age 75 years and older (OR, 0.82 [95% CI, 0.37 to 1.84] vs. 1.13 [95% CI, 0.56 to 2.29]) (24).
Women. As noted previously, only the Chichester study included women (ages 65 to 80 years) in its study population. It found a low prevalence of AAA in women (1.3%), and 75% of screen-detected AAAs in women measured 3.0 to 3.9 cm. There were no statistically significant differences in AAA rupture rate (0.06% in both arms), AAA-specific mortality (<0.2% in both arms), or all-cause mortality (10.7% vs. 10.2%) at 5 years between the invitation to screening and control groups, respectively (8). Event rates in women were very low, and the trial was thus ultimately underpowered to draw definitive conclusions about health outcomes in women. While the individual risk for an AAA rupture at a smaller aneurysm diameter appears to be higher in women than in men (13), the overall AAA rupture rate in women is low due to its uncommon occurrence in the female population. More than two thirds of AAA deaths occur in women age 80 years and older, as reported in the Chichester trial (8).
Large (≥5.5 cm) AAA (standard intervention). Management strategies for large AAA include open surgery and EVAR to avoid arterial rupture.
Open surgical repair, the conventional method for repairing large AAA, has been substantially evaluated in randomized trials, and has been shown to consistently reduce AAA-related mortality in patients with screen-detected AAA (1, 2).
EVAR may provide selective short-term advantages over open surgery, such as avoidance of general anesthesia and reductions in operative time, blood loss, and postoperative pain. Three major trials (EVAR 1, Open Versus Endovascular Repair [OVER], and Dutch Randomized Endovascular Aneurysm Management [DREAM]) compared open surgery with EVAR for the treatment of large AAA; findings suggest that EVAR has a lower operative mortality rate than open surgery, but AAA-specific and all-cause mortality do not differ between the two interventions (27–29). EVAR has a higher reintervention rate than open repair, and generally requires lifelong, regular followup via ultrasonography or CT (1, 2).
Small (3.0 to 5.4 cm) AAA (early intervention). In total, eight RCTs assessed the effects of either early surgery compared with surveillance or pharmacotherapy compared with placebo for the treatment of small AAA.
Two good-quality RCTs (U.K. Small Aneurysm Trial [UKSAT] and Aneurysm Detection and Management [ADAM]) compared early open surgery with surveillance for the treatment of AAAs measuring 4.0 to 5.4 cm (17, 18). In both trials, there was no statistically significant difference between early open surgery and surveillance for all-cause mortality (HR, 0.94 [95% CI, 0.75 to 1.17] and RR, 1.21 [95% CI, 0.95 to 1.54], respectively) after about 5 years. UKSAT continued to find no benefit to early surgery versus surveillance for all-cause mortality with additional (12 years) followup (1, 2).
In the ADAM study, there was also no reduction in risk for AAA-associated mortality in the immediate repair group versus the surveillance group (RR, 1.15 [95% CI, 0.58 to 2.31]), and 30-day postoperative mortality also did not differ (18). In UKSAT, more deaths from ruptured AAA were reported in the surveillance group than in the early intervention group (17 vs. 6 deaths); however, 43% of the lethal ruptures were from AAAs measuring larger than 5.5 cm in diameter, and cause of death was confirmed via autopsy in only 29% of cases (17). Further, the relative magnitude of the effect decreased with additional followup. AAA-related mortality accounted for about 7% of all deaths recorded (1, 2).
These two trials also reported all-cause mortality by subgroups of age and AAA diameter, and showed no statistically significant differences between early open surgery and surveillance in these factors (17, 18). UKSAT also showed no sex-specific differences for all-cause mortality between the arms (17).
Two fair-quality RCTs (Comparison of Surveillance Versus Aortic Endografting for Small Aneurysm Repair [CAESAR] and Positive Impact of Endovascular Options for Treating Aneurysms Early [PIVOTAL]) evaluating early EVAR versus surveillance showed no difference between the two groups in AAA-specific or all-cause mortality or AAA rupture rate after 2 years of followup, although the number of reported events for these outcomes in both trials were small, limiting the certainty of these findings (19, 20).
One good-quality, placebo-controlled, randomized trial of the beta-blocker propranolol showed no statistically significant effect on AAA growth rate, AAA-specific mortality, or all-cause mortality after 2 years of treatment (30).
Pooled analysis of one good- and two fair-quality RCTs evaluating the use of several antibiotics for 4 to 15 weeks revealed no differences in all-cause mortality or surgical procedure rate when compared with placebo. Results were inconsistent for the effect on AAA growth rate (1, 2).
Potential Harms of Screening and Treatment
Each of the four available population-based screening RCTs showed an approximate doubling of all AAA-related operations at 3 to 5 years, driven primarily by an increase in elective surgeries. This overall increase in surgeries persisted at 13 to 15 years, although the magnitude of the difference diminished to some extent (1, 2).
Quality of life and anxiety/depression were evaluated in five small observational studies, with conflicting results. One study showed a statistically significant decrease from baseline in physical functioning, social functioning, and mental health scores in participants who screened positive for AAA at 12 months (31); however, the other four studies did not show similar clinically important effects (1, 2). There were no studies on labeling in patients who screened positive for AAA, although it is a potential harm.
Two good-quality RCTs demonstrated that early open repair (3.0 to 5.4 cm) compared with surveillance for the treatment of small AAA increased the number of surgeries performed by 50% (313 additional surgeries per 1,000 patients), but had no effect on AAA-specific or all-cause mortality, surgical mortality rate, or short-term quality of life (17, 18). Similarly, two fair-quality trials found that early EVAR doubled the rate of AAA-associated surgeries (about 484 to 582 more surgeries per 1,000 patients) compared with surveillance, with no resulting AAA-specific mortality benefit or improvements in quality of life (19, 20).
One RCT of propranolol versus placebo for the treatment of small AAA reported a high discontinuation rate over 2 years (60% of participants receiving the active intervention) due to adverse events, such as fatigue, shortness of breath, and bradycardia (30). Three RCTs of antibiotics found a low rate of adverse events over 4 to 15 weeks (1, 2).
Estimate of Magnitude of Net Benefit
The USPSTF found convincing evidence that screening for AAA in men ages 65 to 75 years who have ever smoked provides a moderate benefit in reducing AAA-specific mortality. Adequate evidence indicates that the harms of AAA screening in this population are at least small. The USPSTF concludes with high certainty that screening for AAA in men ages 65 to 75 years who have ever smoked is of moderate net benefit.
The USPSTF found adequate evidence that screening for AAA in men ages 65 to 75 years who have never smoked provides a small benefit in reducing AAA-specific mortality. Adequate evidence indicates that the harms of AAA screening in this population are at least small. The USPSTF concludes with moderate certainty that screening for AAA in men ages 65 to 75 years who have never smoked is at best of small net benefit.
Only a single screening trial of AAA included women, and it demonstrated no benefit in preventing AAA-specific mortality, overall mortality, or AAA rupture in this population. However, the trial was underpowered for drawing sex-specific conclusions, and as such, does not definitively rule out the possibility of a small benefit, especially among women who are currently smokers. Overall, women have a lower prevalence of AAA than men at any age, and appear to develop AAA at a later age than men. Most ruptures in women occur after age 80 years, when there are many other competing causes of mortality. The USPSTF therefore found inadequate evidence that screening for AAA in women ages 65 to 75 years who have ever smoked provides a benefit in reducing AAA-specific mortality. Adequate evidence indicates that the harms of AAA screening in this population are at least small, and may be higher than in men due to higher rates of operative mortality. The USPSTF concludes that the evidence is insufficient to determine the net benefit of screening for AAA in women ages 65 to 75 years who have ever smoked.
The USPSTF found adequate evidence that screening for AAA in women who have never smoked provides an AAA-specific mortality benefit that can effectively be bounded at zero. Adequate evidence indicates that the harms of AAA screening in this population are at least small, and may be higher than in men due to higher rates of operative mortality. The USPSTF concludes with moderate certainty that screening for AAA in women ages 65 to 75 years who have never smoked is of no net benefit.
How Does Evidence Fit With Biological Understanding?
An AAA is a weakening in the wall of the abdominal section of the aorta. Once a section of the aortic wall is weakened, pressure from the blood flowing through the vessel causes the aorta to bulge or balloon, resulting in the formation of an aneurysm. A large proportion of AAAs are asymptomatic until rupture. AAA rupture can be acute and is life-threatening. Because of this, it is important to consider an effective method for screening and treating appropriate patients before rupture.
Update of Previous USPSTF Recommendation
This recommendation updates the 2005 USPSTF recommendation on screening for AAA. It differs in that instead of one D recommendation for screening for AAA in all women, the USPSTF now has two separate recommendations: an I statement for women who have ever smoked and a D recommendation for women who have never smoked. There continues to be no direct experimental evidence that screening female ever-smokers reduces AAA rupture, AAA-specific mortality, or overall mortality. However, the single RCT of AAA screening that included women was underpowered to draw definitive conclusions by sex, and the prevalence of AAA in currently smoking women approaches that of men who have never smoked. As such, a small net benefit might exist for this population, and appropriate, high-quality research designs should be utilized to address this question.
Recommendations of Others
The American College of Cardiology and the American Heart Association jointly recommend one-time screening for AAA with physical examination and ultrasonography in men age 60 years and older who are the sibling or offspring of a person with AAA and men ages 65 to 75 years who have ever smoked. They do not recommend screening for AAA in men who have never smoked or in women (32). The Society for Vascular Surgery recommends one-time ultrasonography screening for AAA in men age 55 years and older with a family history of AAA, all men age 65 years and older, and women age 65 years and older who have smoked or have a family history of AAA (33). The American College of Preventive Medicine recommends one-time screening in men ages 65 to 75 years who have ever smoked; it does not recommend routine screening in women (34). The Canadian Society for Vascular Surgery recommends ultrasonography screening for AAA in men ages 65 to 75 years who are candidates for surgery and willing to participate. In individualized cases, some women older than age 65 years with multiple risk factors for AAA (smoking history, cerebrovascular disease, or family history) may be considered for screening (35). The European Society for Vascular Surgery recommends that men should be screened for AAA with a single ultrasound at age 65 years, but screening should be considered at an earlier age in men at higher risk (e.g., men who smoke, have other cardiovascular disease, or have a family history). It notes that in general, screening in older women does not reduce the incidence of aneurysm rupture, but screening women who smoke may require further investigation (36).
Table 1: What the Grades Mean and Suggestions for Practice
Table 2: Levels of Certainty Regarding Net Benefit
|Level of Certainty*||Description|
|High||The available evidence usually includes consistent results from well-designed, well-conducted studies in representative primary care populations. These studies assess the effects of the preventive service on health outcomes. This conclusion is therefore unlikely to be strongly affected by the results of future studies.|
|Moderate||The available evidence is sufficient to determine the effects of the preventive service on health outcomes, but confidence in the estimate is constrained by factors such as:
As more information becomes available, the magnitude or direction of the observed effect could change, and this change may be large enough to alter the conclusion.
|Low||The available evidence is insufficient to assess effects on health outcomes. Evidence is insufficient because of:
More information may allow an estimation of effects on health outcomes.
*The U.S. Preventive Services Task Force defines certainty as "likelihood that the USPSTF assessment of the net benefit of a preventive service is correct." The net benefit is defined as benefit minus harm of the preventive service as implemented in a general, primary care population. The USPSTF assigns a certainty level based on the nature of the overall evidence available to assess the net benefit of a preventive service.
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AHRQ Publication No. 14-05202-EF-2
Current as of January 2014
U.S. Preventive Services Task Force. Screening for Abdominal Aortic Aneurysm: Draft Recommendation Statement. AHRQ Publication No. 14-05202-EF-2. http://www.uspreventiveservicestaskforce.org/draftrec.htm