Red light or green light for AAA screening?

Editor’s note: Last week I put up a post, Blue light special: AAA screening at Kmart in the disease-mongering aisle, that attracted some interesting and thoughtful comments. In particular, the exchange between Dan Hackam, an old online friend, and Joe Ross, a researcher who I quoted in the piece, is worthy of more attention than it might otherwise receive buried in the comments section. Here is that exchange:

Dan Hackam, on September 16, 2010 at 6:17 PM wrote:

Larry there are new data on who to screen for AAA. This not an RCT.

Analysis of risk factors for abdominal aortic aneurysm in a cohort of more than 3 million individuals

K. Craig Kent, MDa, Robert M. Zwolak, MDa, Natalia N. Egorova, PhD, MPHb, Thomas S. Riles, MDa, Andrew Manganaro, MDa, Alan J. Moskowitz, MDb, Annetine C. Gelijns, PhDb, Giampaolo Greco, PhD, MPHb
Received 17 February 2010; accepted 4 May 2010. published online 14 July 2010.

Background: Abdominal aortic aneurysm (AAA) disease is an insidious condition with an 85% chance of death after rupture. Ultrasound screening can reduce mortality, but its use is advocated only for a limited subset of the population at risk.

Methods: We used data from a retrospective cohort of 3.1 million patients who completed a medical and lifestyle questionnaire and were evaluated by ultrasound imaging for the presence of AAA by Life Line Screening in 2003 to 2008. Risk factors associated with AAA were identified using multivariable logistic regression analysis.

Results: We observed a positive association with increasing years of smoking and cigarettes smoked and a negative association with smoking cessation. Excess weight was associated with increased risk, whereas exercise and consumption of nuts, vegetables, and fruits were associated with reduced risk. Blacks, Hispanics, and Asians had lower risk of AAA than whites and Native Americans. Well-known risk factors were reaffirmed, including male gender, age, family history, and cardiovascular disease. A predictive scoring system was created that identifies aneurysms more efficiently than current criteria and includes women, nonsmokers, and individuals aged <65 years. Using this model on national statistics of risk factors prevalence, we estimated 1.1 million AAAs in the United States, of which 569,000 are among women, nonsmokers, and individuals aged <65 years.

Conclusions: Smoking cessation and a healthy lifestyle are associated with lower risk of AAA. We estimated that about half of the patients with AAA disease are not eligible for screening under current guidelines. We have created a high-yield screening algorithm that expands the target population for screening by including at-risk individuals not identified with existing screening criteria.

Thanks, Dan. I’ve forwarded the note to Joe. I also found a nice article in Heartwire on the paper. In truth, I am completely in favor of more and better data to improve screening. What I’m completely opposed to is when a company or other interested group or groups hijacks the process.

Dan Hackam, on September 16, 2010 at 8:21 PM wrote:

Larry, I have found many AAA in patients who would never be candidates based on the USPSTF criteria. I can understand the wariness among many about industry pushing a screening test (kind of like how drug companies advertise on TV for lipitor, huh?). But if it leads to increased detection of a potentially preventable adverse event, together with increased referrals (and therefore better risk factor modification, something that has been documented once AAA has been detected and referred), then I am all for it. Patients should not get stenting or surgery for AAA<5.5 cm unless they have other risk factors for rupture (such as rapid growth in the past year of serial scanning, a family history of rupture, and possibly women and smokers). In most hands they wouldn’t. If this leads to harms (and AAA surgery does carry a 5% risk of mortality in good hands), then it’s a shame. But compared to the massive underdiagnosis of AAA (ie most ruptured AAA occur in patients with unknown disease who could have been scanned/studied, and most ruptured AAA 85-90% are fatal), I don’t think it’s such a bad thing. If Pfizer set up a cholesterol-screening tent in K-mart, I don’t think people would complain. Erectile dysfunction drug makers are all over questionnaires for detecting ED; Sanofi-Aventis flogs peripheral arterial disease on commercials because clopidogrel was proven beneficial in PAD in the CAPRIE study. etc. etc.

Joseph Ross, on September 16, 2010 at 10:41 PM wrote:

Dan, thanks for passing along. While the study uses a unique data source and is definitely hypothesis generating, in my opinion, the analysis is very limited.

It’s a retrospective analysis of a cohort of self-referred individuals who paid for the test out of pocket and AAAs were defined as aneurysms ≥ 3cm. To be convincing, the study needs to be prospectively conducted to identify patient characteristics that are associated with AAA, or at least a good retrospective case-control study.

And even in this analysis, age and smoking status were by far the most important predictors of AAA.

The purpose of screening is not to identify AAAs; the purpose of screening is to identify AAAs that are likely to have a clinical impact on the patient and are at a stage where they can be intervened upon successfully.

This study doesn’t get us there.

Also, my point to Larry was about considering what happens in terms of false-positives when a screening strategy is adopted that includes a lower risk population.

I only read this article quickly, but these authors’ numbers bear this out as well. In the story it’s clarified:

“Therefore, the authors point out that a decision on which number to use as a threshold score may come down to cost, because a lower threshold score for screening would identify more aneurysms but also require more ultrasound studies as well as follow-up testing. For example, focusing only on the cost of the initial screening test, setting the cutoff at 42 would lead to the identification of 680 000 aneurysms in the population aged 50 to 75, but at the expense of 24 907 000 ultrasound studies. Raising the cutoff to 65 would yield half as many aneurysms but will require only one-fifth as many ultrasound studies.”

And the numbers would look even worse if they were calculated for a AAA as defined as 5 or 5.5cm, instead of 3cm.


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