August 24, 2010
INTERVENTIONAL/SURGERY
THREE-MILLION PATIENT STUDY YIELDS NEW AAA RISK-SCORE SYSTEM | Reed Miller

Chicago, IL - Analysis of a database of 3.1 million patients has yielded a new scoring system for abdominal aortic aneurysm (AAA) that is much more complex but also more effective than the current simple guidelines for AAA screening, according to its authors [1].

The current United States Preventive Services Task Force (USPSTF) guidelines recommend AAA screening for men aged 65 to 75 years with a history of smoking, but at least 33% of ruptured AAA hospitalizations and 41% of aortic-aneurysm deaths are among women, and 22% of AAA-related deaths occur in nonsmokers, according to the Society for Vascular Surgery's screening task force, led by Dr K Craig Kent (University of Wisconsin, Madison), the authors of a new study that was published online July 14, 2010 in the Journal of Vascular Surgery.

Because the current national guidelines for AAA screening fail to target some of the populations that suffer many AAA ruptures, Kent et al retrospectively analyzed medical and questionnaire data from 3.1 million patients screened with ultrasound for AAA between 2003 to 2008.

They identified risk factors associated with AAA with a multivariable logistic regression analysis. The analysis affirmed the previously well-known risk factors—male gender, age, family history, cardiovascular disease, and past smoker—but also discovered several new markers of higher or lower risk. 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.

The study also found that the risk of AAA increased with more years of smoking and total cigarettes smoked (based on packs-per-day estimates), while the risk went down the longer the patient lived after quitting smoking. These findings were "very dramatic and hadn't been demonstrated before," Kent told heartwire in an interview.

New scoring system to improve screening

Combining their findings with data from the National Health and Nutrition Examination Survey, a cross-sectional survey of the civilian noninstitutionalized US population, Kent et al calculate that there are currently about 1.1 million AAAs (prevalence 1.4) in the US population aged 50 to 84, of which the current USPSTF criteria would catch less than 30%.

So, based on their findings from the database, Kent et al created a new scoring system that would assign points to different risk factors, with negative points for factors that decrease AAA risk. For example, in their scoring system, smoking could add between 1 to 26 points to the patient's risk score, depending on the duration and severity of their habit, and points are taken off for years since quitting. Being Hispanic or Asian subtracts four points, while being aged 80 to 84 adds 35 points.

The authors suggest that patients with a score of 42 or above should be screened for AAA. This is also the point where the system has the best discriminative ability and would identify 88.6% of all AAAs, if applied to a population aged 50 to 84 years, or 59%, if applied to people 50 to 75 years old. For example, 42 corresponds to a 65-year-old male former smoker, with no other risk factors, who smoked less than half a pack per day and quit more than 10 years ago.

"The drawback is that the new scoring system is more complicated than the current system. . . . Applying a scoring system like this rather than a one-sentence description of whom to screen is going to be more complicated," Kent said. But "the upside is fairly significant, which is that a lot of people who currently die of ruptured aneurysms are missed by the current criteria, and this scoring system allows us to capture those individuals."

Kent added that before his group's scoring system can become part of Medicare's screening-coverage policy or replace the current USPSTF guidelines, it must be prospectively studied in another very large group of patients to see whether it identifies as many AAAs as their retrospective analysis predicts.

Also, although ultrasound screening tests for AAA are relatively inexpensive per test, a populationwide screening program covering millions of people could become very expensive for Medicare, Kent said.

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. "The threshold score that is chosen will be a critical decision that will depend on many factors, with cost and ultimately cost-effectiveness leading the list," the authors conclude.