Analysis of clinical benefit, harms, and cost-effectiveness of screening women for abdominal aortic aneurysm

Abstract

Background: A third of deaths in the UK from ruptured abdominal aortic aneurysm (AAA) are in women. In men, national screening programmes reduce deaths from AAA and are cost-effective. The benefits, harms, and cost-effectiveness in offering a similar programme to women have not been formally assessed, and this was the aim of this study.

Methods: We developed a decision model to assess predefined outcomes of death caused by AAA, life years, quality-adjusted life years, costs, and the incremental cost-effectiveness ratio for a population of women invited to AAA screening versus a population who were not invited to screening. A discrete event simulation model was set up for AAA screening, surveillance, and intervention. Relevant women-specific parameters were obtained from sources including systematic literature reviews, national registry or administrative databases, major AAA surgery trials, and UK National Health Service reference costs.

Findings: AAA screening for women, as currently offered to UK men (at age 65 years, with an AAA diagnosis at an aortic diameter of ≥3·0 cm, and elective repair considered at ≥5·5cm) gave, over 30 years, an estimated incremental cost-effectiveness ratio of £30 000 (95% CI 12 000-87 000) per quality-adjusted life year gained, with 3900 invitations to screening required to prevent one AAA-related death and an overdiagnosis rate of 33%. A modified option for women (screening at age 70 years, diagnosis at 2·5 cm and repair at 5·0 cm) was estimated to have an incremental cost-effectiveness ratio of £23 000 (9500-71 000) per quality-adjusted life year and 1800 invitations to screening required to prevent one AAA-death, but an overdiagnosis rate of 55%. There was considerable uncertainty in the cost-effectiveness ratio, largely driven by uncertainty about AAA prevalence, the distribution of aortic sizes for women at different ages, and the effect of screening on quality of life.

Interpretation: By UK standards, an AAA screening programme for women, designed to be similar to that used to screen men, is unlikely to be cost-effective. Further research on the aortic diameter distribution in women and potential quality of life decrements associated with screening are needed to assess the full benefits and harms of modified options.

Funding: UK National Institute for Health Research Health Technology Assessment programme.

Figure 1

Aneurysm deaths and aneurysm repairs for reference case and best alternative strategy Data for reference case and best alternative strategy are shown. Reference case: invitation to screening at age 65 years, diagnosis threshold 3·0 cm; intervention threshold 5·5 cm. Best alternative strategy: invitation to screening at age 70 years, diagnosis threshold 2·5 cm, intervention threshold 5·0 cm. Differences in elective operations, emergency operations and AAA deaths in 1 million women (invited to screening minus not invited to screening group; A). Percentage reduction in number of AAA deaths from screening by age (B). Because of small number volatility, the percent reduction in AAA deaths is not shown when the number of AAA deaths is less than 50 (approximately the first year after invitation to screening). AAA=abdominal aortic aneurysm.

Figure 2

Cost-effectiveness acceptability curves of invitation to AAA screening from the probabilistic sensitivity analyses. Willingness-to-pay is the amount that a particular health provider is prepared to pay for each additional QALY of benefit, which for the National Institute of Health and Care Excellence is usually considered in the range of £20 000–30 000. AAA=abdominal aortic aneurysm. QALY=quality-adjusted life year. The probability of cost-effectiveness at £20 000 per QALY is 0·18 for the reference case and 0·42 for the best alternative strategy.

Figure 3

Tornado plot showing ICER estimates for sensitivity analyses. Blue bars show a decrease in the ICER from the reference case (grey vertical line; £30 170), red bars show an increasing ICER from the reference case. Details of changes to all parameter values are given in the appendix. ICER=incremental cost-effectiveness ratio. AAA=abdominal aortic aneurysm. NAAASP=National Abdominal Aortic Aneurysm Screening Programme. NVR/HES=National Vascular Registry/Hospital Episode Statistics. QALY=quality-adjusted life year. *Health-related quality of life decrements for diagnosis, surgery, and non-intervention for elective surgery (appendix). †Used the NAAASP-based distribution but doubled and halved the AAA prevalence. ‡NAAASP-based AAA distribution was replaced with one based on 5140 women aged 70 years screened in Sweden, while keeping the prevalence of AAA constant. §Halved and doubled the drop-out from surveillance and incidental detection rates simultaneously. ¶Reduced (by 20%) and increased (by 25%) the screening, surveillance, and consultation costs. ||Reduced (by 20%) elective surgery costs while increasing (by 25%) emergency surgery costs, and vice-versa. **Allowed non-intervention rate to depend on age. ††Sensitivity of operative parameters investigated by using systematic review data (rather than NVR/HES) to inform elective and emergency operative parameters., ‡‡Reduced the open repair operative mortality from 8·1% estimated from NVR/HES to 5%. §§Increased re-intervention rate after elective open repair and AAA mortality after emergency repair.