Abdominal Aortic Aneurysm Screening in Sweden
How has abdominal aortic aneurysm (AAA) screening affected disease-specific mortality, incidence, and surgery?
Individual data on the incidence of AAA, AAA mortality, and surgery for AAA in a cohort of men ≥65 years invited to screening between 2006 and 2009, were compared with an age-matched contemporaneous cohort of men who were not invited for screening. National data for all men aged 40–99 years between January 1, 1987, and December 31, 2015, were used to explore background trends. Adjustment for confounding was done using propensity scores obtained from a logistic regression model on cohort year, marital status, educational level, income, and whether the patient already had an AAA diagnosis at baseline.
AAA mortality in Swedish men has decreased from 36 to 10 deaths per 100,000 men aged 65–74 years between the early 2000s and 2015. Mortality decreased at similar rates regardless of whether AAA screening was offered. A nonsignificant reduction in AAA mortality associated with screening was identified after 6 years (adjusted odds ratio [aOR], 0.76; 95% confidence interval [CI], 0.38–1.51); two men (95% CI, –3 to 7) avoided death from AAA for every 10,000 men offered screening. Screening was associated with increased odds of AAA diagnosis (aOR, 1.52; 95% CI, 1.16–1.99; p = 0.002) and an increased risk of elective surgery (aOR, 1.59; 95% CI, 1.20–2.10; p = 0.001), such that for every 10,000 men offered screening, 49 men (95% CI, 25–73) were likely to be overdiagnosed, 19 of whom (95% CI, 1–37) had avoidable surgery that increased their risk of mortality and morbidity.
AAA screening in Sweden did not contribute substantially to the large observed reductions in AAA mortality. The reductions were mostly caused by other factors, probably reduced smoking. The small benefit and less favorable benefit-to-harm balance call the continued justification of the intervention into question.
The concept of overdiagnosis is relevant to the costs and potential harms of elective AAA repair, particularly if providers are incentivized or otherwise biased toward performing repair below evidence-based diameter thresholds. In these scenarios, risk and cost are shouldered without associated benefit. The definition of overdiagnosis within this analysis, “detection of aneurysms that would not have caused symptoms during the person’s life or caused their death,” however, assumes that the patient’s survival and future behavior of the aneurysm are both known. Aneurysm diameter was not included in this analysis, however, and the cumulative survival benefit from screening likely continues to accrue beyond the 6-year time point used in this analysis. As mentioned in the invited commentary that accompanies this analysis, other data from Sweden suggesting a 10-year timeline is appropriate for assessing the mortality impact. These results must be considered alongside prospective trials of AAA screening that have demonstrated a significant survival benefit.
It is also important to acknowledge that population-specific factors (e.g., race, ethnicity, smoking, and other health risk behaviors) may limit the external validity of these observations beyond Sweden. Similarly, widespread availability of screening may have different implications in populations where access is limited by insurance coverage, capacity of the healthcare system, or awareness.
Anyone who has taken care of a ruptured AAA can understand the rationale for screening. Ultimately, benefit from identification of an asymptomatic AAA depends on evidence-based use of elective repair performed with low rates of morbidity and mortality.
Keywords: Aortic Aneurysm, Abdominal, Morbidity, Risk, Secondary Prevention, Smoking, Surgical Procedures, Elective, Sweden, Vascular Diseases
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