Criteria for a good screening test
3. Which of the following is not one of the World Health Organization’s guiding principles for adopting a screening test?
- The disease must be common, or it must have grave consequences if it is not detected
- The disease must be detectable in a latent or early stage
- A screening test must exist that is acceptable to patients
- A treatment must exist that affects the natural history of the disease and its prognosis
- The cost of screening must be reasonable
- The screening test must have high sensitivity and specificity
In 1968, the World Health Organization published guidelines that continue to be used to determine the acceptability of screening tests.23 These principles state that for a screening test to be acceptable, the disease must be highly prevalent or result in grave consequences if not detected. The disease must have a latent or early stage in which it can be detected, and treatment must be available at that stage that affects the natural history and prognosis of the illness. The test must also be acceptable to patients physically, and the cost of it should be balanced in relation to possible expenditure on medical care as a whole.
As discussed previously, abdominal aortic aneurysms are common, and the consequences of rupture are grave. If the condition is detected early, treatment is available that can be lifesaving. Additionally, abdominal ultrasonography is noninvasive and inexpensive (costing roughly a few hundred dollars).24 Therefore, all of the World Health Organization criteria are satisfied. Improved outcomes with newer endovascular techniques for repair23 will likely also improve the value of screening.
Although high sensitivity and specificity are not required to satisfy the criteria, abdominal ultrasonography is nearly 100% sensitive and specific for detecting abdominal aortic aneurysms in patients without symptoms.12
Given the prevalence of the disease, by one estimate, if current USPSTF guidelines are followed (ie, if we screen only men age 65 to 75 who have ever smoked), for every 20 men we screen, we would detect one abdominal aortic aneurysm, and we would detect 29.5% of all of these aneurysms.2 If we screen all patients age 50 to 84, 74 people would need to be screened to detect one abdominal aortic aneurysm, but a much greater percentage of all of these aneurysms would be detected.
SHOULD OTHER GROUPS BE SCREENED?
4. The patient has a 40-year-old daughter who has hypertension and a 20-pack-year history of smoking. Should she be screened for an abdominal aortic aneurysm?
The 2005 USPSTF report recommends onetime ultrasonographic screening for all men age 65 to 75 who have ever smoked.1
The American Heart Association made a similar recommendation in 2005 in conjunction with the Society for Vascular Surgery, the American Association of Vascular Surgery, the Society for Vascular Medicine and Biology, and others.25 However, these groups also support screening men age 60 and older who are siblings or children of patients with abdominal aortic aneurysms, using physical examination and abdominal ultrasonography.
Both of the guidelines exclude women (who account for 41% of all deaths from this disease by one estimate) and nonsmokers (who account for 22%).2
The USPSTF makes no recommendation about nonsmokers, but it specifically recommends against screening women, stating that women have a low prevalence of large abdominal aortic aneurysms and that few women die of this disease. Therefore, according to the USPSTF, the risks of early treatment in women—including morbidity and death with surgical treatment and associated psychological harms—are not worth the benefits.1
However, a study of 3.1 million Americans found that women who have multiple cardiovascular risk factors such as smoking, hypertension, hyperlipidemia, and a family history of abdominal aortic aneurysm are at as great or greater risk of abdominal aortic aneurysm as men who fit the USPSTF criteria.2 Additionally, a positive family history of abdominal aortic aneurysm was among the strongest predictors of a diagnosis of abdominal aortic aneurysm on screening.2
Since 2005, newer guidelines have been released that broaden the recommendations for who should be screened. The Society for Vascular Surgery12 recommends screening:
- All men age 65 and older
- Men age 55 and older and women age 65 and older who have a family history of abdominal aortic aneurysm
- Women age 65 and older who have ever smoked.
A recent Swedish study demonstrated that the prevalence of abdominal aortic aneurysms in siblings of patients known to have this condition is significantly higher than in the general population; of the siblings who were screened, 11% had an abdominal aortic aneurysm, as did 17% of brothers and 6% of sisters.26
Nevertheless, broadened screening remains controversial, and more investigations of family history-based screening are ongoing.
WHEN DOES AN ABDOMINAL AORTIC ANEURYSM NEED SURGERY ?
Our patient was diagnosed with an infrarenal abdominal aortic aneurysm 6.5 cm in diameter and with bilateral common iliac artery aneurysms measuring 3.8 cm on the left and 5.2 cm on the right.
Computed tomography (CT) was done for preoperative planning (Figures 1 and 2), as it can define the aneurysm better for surgical intervention. Ultrasonography, while nearly 99% sensitive and specific for finding abdominal aortic aneurysms,12 does not provide the view of the abdominal anatomy that may be needed in surgical planning. The patient was seen by a vascular surgeon, and appropriate preoperative testing was done; the results showed that his risk during an open surgical procedure would be slightly above average.
The decision that needed to be made in this case was whether the patient should undergo surgery (either open or endovascular) or only medical intervention. In two randomized controlled trials comparing immediate intervention vs ongoing surveillance, the best threshold for surgical intervention was an aneurysm larger than 5.5 cm.27–29 Both trials found no benefit in terms of survival with surgical repair of aneurysms 4.0 to 5.4 cm: there was no long-term difference in the rate of survival in patients who underwent early surgical intervention compared with surveillance until the aneurysm was larger than 5.5 cm.
But this was with open surgery. What about endovascular repair? More recent studies that evaluated endovascular repair of small aneurysms (4.0–5.0 cm) found no improvement in end points, including time to aneurysm rupture and rate of aneurysm-related death, compared with surveillance.30,31
Treat risk factors
Medical therapy currently focuses on reducing risk factors for aneurysm growth and rupture, including hypertension, hyperlipidemia, and smoking, but research is focusing on angiotensin-converting enzyme inhibitors and experimental agents such as metalloproteinase inhibitors.32,33
Smoking is a major risk factor in the development, growth, and rupture of abdominal aortic aneurysms,34 and the 2005 joint guidelines of the American College of Cardiology and the American Heart Association (ACC/AHA) recommend that everyone with an abdominal aortic aneurysm or a family history of it be advised to stop smoking.25 This is especially important in light of data that show a higher risk of abdominal aortic aneurysm with a higher volume of smoking (total pack-years) and a decrease in risk with time since quitting.2
Medical management also includes treating other associated cardiovascular risk factors, including hypertension and dyslipidemia. The ACC/AHA guidelines recommend that patients with abdominal aortic aneurysms be treated similarly to patients with atherosclerotic disease or a coronary artery disease equivalent, including giving them a statin and an antiplatelet drug such as aspirin.
The ACC/AHA guidelines also recommend that patients who are managed medically and have an aneurysm of 3.0 to 4.0 cm undergo ultrasonographic monitoring every 2 to 3 years, and those with an aneurysm of 4.0 to 5.4 cm undergo monitoring with ultrasonography or CT every 6 to 12 months.25