Who should be screened for an abdominal aortic aneurysm?

If you are a man aged 65 to 75 who has ever smoked, US guidelines recommend a single ultrasound scan to check for an abdominal aortic aneurysm; for most women, and for men who never smoked, they do not [s1]. The reasoning is a careful weighing of who actually gains from finding a symptomless bulge in the body's largest artery [s1].

An abdominal aortic aneurysm is an enlargement of the aorta to a diameter of 3.0 cm or more, and most are silent until they rupture — a catastrophe whose associated risk of death is as high as 81% [s1]. Put that way, catching one early sounds obviously worthwhile. Screening only earns its place, though, if finding aneurysms early prevents enough deaths to outweigh the harms of looking, and those harms are not trivial.

Does screening save lives?

For the group where it has been tested, yes. Pooling the randomised trials, inviting men to be screened was associated with a 35% reduction in deaths from aneurysm (Peto odds ratio 0.65; 95% confidence interval 0.57 to 0.74) [s1]. It also cut emergency surgery (Peto odds ratio 0.57; 95% confidence interval 0.48 to 0.68) [s1]. The catch is scale: the number needed to screen was 305 men (95% confidence interval 248 to 411) to prevent one aneurysm death, and 246 men (95% confidence interval 207 to 311) to prevent one rupture [s1]. And the trial evidence comes almost entirely from men aged 65 to 75, which is why the guidance is written so narrowly [s1].

The four verdicts

The US Preventive Services Task Force does not issue one recommendation but four, graded by how favourable the balance of benefit and harm is [s1]:

• Men aged 65 to 75 who ever smoked — recommended (Grade B). One-time ultrasound screening, the group with the clearest net benefit [s1].
• Men aged 65 to 75 who never smoked — selective (Grade C). Clinicians should offer it case by case rather than screen everyone, because the net benefit across the whole group is small [s1].
• Women aged 65 to 75 who ever smoked or have a family history — insufficient evidence (I statement). The Task Force could not determine the balance of benefits and harms [s1].
• Women who never smoked and have no family history — recommended against (Grade D). Here it concluded the harms outweigh the benefits [s1].

Why the sex split

Two things drive the caution about women. Aneurysms are less common in them, and the randomised evidence was gathered in men, so the benefit is unproven rather than disproven for women [s1]. But the harms of treatment also fall harder on women. After endovascular repair, 30-day mortality was 2.31% in women versus 1.37% in men (odds ratio 1.67; 95% confidence interval 1.38 to 2.04), and after open repair 5.37% versus 2.82% (odds ratio 1.76; 95% confidence interval 1.35 to 2.30), differences attributed partly to more complex anatomy and smaller vessels [s1]. When a screen finds an aneurysm, some of those found will be sent toward an operation, and the operation itself is riskier in the very group the evidence is thinnest for. That is the overdiagnosis problem in miniature.

Where the specialists go further

This is a case where the surgical societies would screen more people than the Task Force endorses. The Society for Vascular Surgery recommends one-time ultrasound screening for all men and women aged 65 to 75 with a history of tobacco use, men aged 55 or older with a family history, and women aged 65 or older who have smoked or have a family history [s1] [s2]. The American College of Cardiology and American Heart Association recommend one-time screening in men aged 65 to 75 who ever smoked, or men 60 or older who are the sibling or offspring of someone with an aneurysm, and do not recommend screening men who never smoked or women [s1]. So the vascular surgeons would scan some of the women the Task Force leaves at "insufficient evidence" — a defensible disagreement, given that a family history through a female first-degree relative raises aneurysm risk more (odds ratio 4.32) than through a male one (odds ratio 1.61) [s1].

What it means for a reader

Sex and smoking history, not general worry, determine whether this scan is worth having: a symptomless person outside the defined groups gains little and takes on the harms of chasing a rare finding [s1]. It is the same logic that governs carotid screening in people with no symptoms and what imaging reveals about silent atherosclerosis in the arteries of healthy people. None of this bears on symptoms: sudden severe abdominal or back pain with faintness is a medical emergency, not a screening question.