A 67-year-old man presented for evaluation of an abdominal aortic aneurysm, noted 1 month previously after his primary care physician ordered screening ultrasonography as part of a routine annual physical examination. The man was experiencing no symptoms.
He had type 2 diabetes mellitus, chronic obstructive pulmonary disease, hypertension, and hyperlipidemia. He smoked two packs of cigarettes a day. He had never had surgery. His current medications included diltiazem, fenofibrate, niacin, and aspirin; because he had chronic obstructive pulmonary disease, he was not on a beta-blocker.
His father had died suddenly at the age of 77; his death was attributed to a cardiac cause, but no formal autopsy was performed. Neither the patient’s siblings nor his children were screened for aneurysms.
On physical examination, he was comfortable and in no acute distress. His blood pressure was 156/71 mm Hg, pulse 60, temperature 36.1°C (97.0°F), and body mass index 30.15 kg/m2, which is in the obese range.
He had no jugular venous distention, no carotid bruits, and no lymphadenopathy. The cardiac examination was unremarkable, with regular rate, normal sinus rhythm, and no murmurs. On pulmonary examination, inspiratory and expiratory wheezes were noted in all lung fields.
His abdomen was obese but not tender to palpation. The aneurysm was not palpable. His pedal pulses were normal. The remainder of the examination was normal.
WHO SHOULD BE SCREENED?
1. For which of the following groups does the United States Preventive Services Task Force (USPSTF) strongly recommend screening for abdominal aortic aneurysms?
- Men and women over age 65
- Men and women who have ever smoked and are over age 65
- Men over age 75 and men over age 65 who smoke
- Men age 65 to 75 who have ever smoked
In 2005, the USPSTF recommended one-time screening ultrasonography for all men age 65 to 75 who have ever smoked. On the basis of evidence available at the time, it made no recommendation for men age 65 to 75 who have never smoked, and it recommended against screening women.1
ANEURYSMS ARE COMMON, OFTEN ASYMPTOMATIC, UNTIL THEY RUPTURE
Abdominal aortic aneurysms are relatively common in older adults, with a prevalence of 1.4% in the US population age 50 to 84 years.2 In four randomized controlled trials of aneurysm screening in Europe and Australia, the prevalence of any aneurysm (not just abdominal aortic aneurysms) in men was 6% (95% confidence interval 5–6).3–6
Fewer studies are available on the prevalence in women. One study found a prevalence of 0.7% in 10,012 US women, compared with 3.9% in men.7
In a recent report of the aneurysm screening program in the United Kingdom, the incidence of aneurysms had decreased from historically reported estimates.8,9
In the year 2000, abdominal aortic aneurysms caused 15,000 deaths in the United States and were the 10th leading cause of death in white men age 65 to 74.10 The actual number of deaths may be larger, since some people may die suddenly of an aneurysm with no evaluation for attributable cause.11
Aortic aneurysms are often asymptomatic until they rupture, making them difficult to detect without a focused screening program. The goal of treatment is to avoid spontaneous rupture and death. When aneurysms rupture, the estimated death rate is 80%.6
EVIDENCE IN FAVOR OF SCREENING
Ultrasonography is nearly 100% sensitive and specific in detecting abdominal aortic aneurysms in patients without symptoms.12 In comparison, abdominal palpation is 68% sensitive and 75% specific.13
The larger the aneurysm, the higher the risk of rupture.14–16 The annual risk of rupture is:
- 0.5% with aneurysms smaller than 4.0 cm
- 1.0% with aneurysms 4.0–4.9 cm
- 11% with aneurysms 5.0–5.9 cm
- 26% with aneurysms 6.0–6.9 cm.
Several large randomized controlled trials in men over age 65 evaluated the effect of screening programs for abdominal aortic aneurysms on the rate of deaths from this cause.3–6,17 A meta-analysis of these trials found a relative risk of 0.60 in favor of screening—ie, men over age 65 who were screened had a 40% lower risk of dying of an abdominal aortic aneurysm than men who were not screened.18 In long-term follow-up, the rate continued to be about 50% lower with screening than without.19,20 The absolute reduction in risk of death was 0.13%.21
Absolute risk reduction and number needed to screen
2. If screening offers an absolute risk reduction in the death rate of 0.13%, how many need to be screened to prevent one death?
The number of patients that need to be screened to prevent one death is called the number needed to screen.22 It is calculated as 1 divided by the absolute risk reduction. Therefore, in screening for abdominal aortic aneurysms, the number needed to screen is 1/0.0013, or 769. Recall that these numbers are from men over age 65, with no upper limit in age. If we consider only men age 65 to 75, the absolute risk reduction is 0.16%, which corresponds to a number needed to screen of 625.
To put this in perspective, the number of people who need to be screened using fecal occult blood testing to prevent one death from colon cancer is 808, and the number of women who need to undergo mammography to prevent one breast cancer death is 1,887.21,22