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NIHR Signal Abdominal aortic aneurysm screening for women is unlikely to be a fair use of NHS resources

Published on 13 November 2018

doi: 10.3310/signal-000676

Nearly 4,000 women would need screening to prevent one death, and a third of aneurysms detected wouldn’t have influenced the individual woman's health or lifespan.

Aneurysm rupture is a life-threatening emergency with low survival. Men are known to be at higher risk of an aneurysm and are offered screening at age 65 to allow early diagnosis of aneurysms large enough to warrant surgical repair. However, a third of deaths from rupture are in women.

This NIHR-funded study is the first to model the potential benefits, harms and cost-effectiveness of abdominal aortic aneurysm screening in women. All screening scenarios were estimated to exceed the NHS cost-effectiveness threshold of £20,000 to £30,000 per year of quality life gained.

The review supports the current recommendation to screen men only.

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Why was this study needed?

Abdominal aortic aneurysm (AAA) is typically defined as widening of the abdominal aorta to a diameter of 3cm or more. It is about three times more common in men than women. The British Society of Interventional Radiology reports that, in England, 4% of men aged 65-74 (about 80,000) have AAA, resulting in around 6,000 deaths each year. If an aneurysm ruptures, mortality is greater than 80%. Because of this older men are screened so that if an aneurysm is detected with a diameter 5.5 cm or more elective surgical repair can be performed.

Screening also carries potential drawbacks. Treatment carries a risk of mortality, although this should be below 5%, and there are psychological effects of detecting aneurysms below the treatment threshold.

In men, the balance of evidence weighs towards more benefits than harms of screening. In women, the evidence has been less clear.

What did this study do?

This was a decision model analysing the health outcomes and cost-effectiveness of population-based AAA screening for women compared with no screening. Information such as aneurysm prevalence, growth rates, operative mortality and quality of life, came from systematic literature reviews, clinical trials, hospital datasets and registry data. NHS costs included those for invitation, screening, and consultation, elective and emergency surgery.

The baseline model used the same screening pathway as currently used for men. A total of 12 different screening scenarios were tested, increasing the age at screening or thresholds for diagnosis or elective surgery, to derive the most cost-effective option.

Simulation studies are valuable when running a screening trial would require a large sample size and follow-up, and may result in patient harms. However, assumptions in the model may be based on inaccurate or uncertain data.

What did it find?

  • In this model, using the same criteria as for UK men, screening increased detection among women aged 65-95 by 23% compared with no screening (an additional 2,168 cases per million). It resulted in an additional 452 elective operations per 1 million women screened (a 21% increase). However, 33% of screen-detected AAAs would not have been otherwise detected or ruptured during the woman’s lifetime (over-diagnosis). Meanwhile, 13% of those repaired wouldn't have led to death or surgery in the absence of screening (over-treatment).
  • In this model, there were 257 fewer AAA-related deaths per million women (3% decrease). However, for every four women who avoided AAA-related death because of successful screening, one woman died due to elective surgical repair. Overall, 3,900 women need screening to prevent one AAA-related death.
  • The best alternative strategy modelled – screening at age 70 years with lower thresholds for diagnosis (2.5cm) and surgical referral (5.0cm) – gave a 66% increase in AAA detection (9,089 per million). There were an additional 1,301 elective operations per million women (55% increase). However, the rate of over-diagnosis increased to 55% and the rate of over-treatment to 24%.
  • This strategy resulted in 566 fewer AAA-related deaths per million women (8% decrease). However, for every seven women who avoided AAA-related death because of successful screening, two died due to elective surgical repair. Overall, 1,800 women need screening to prevent one AAA-related death.
  • Using the same screening criteria as for UK men, inviting women to screening gave an additional 0.0011 quality adjusted life years (QALYs) at the cost of £30,170 (95% confidence interval [CI] £12,238 to £87,002) per QALY gained. The best alternative strategy in the model gave 0.0020 QALY gain at an additional cost of £22,540 (95% CI £9,522 to £70,638) per QALY gained.

What does current guidance say on this issue?

Public Health England offers AAA screening to men aged 65 years. Normal aortas (less than 3 cm diameter) require no further scans. Men with a small aneurysm (3.0 to 4.4 cm) are given a repeat scan at 12 months and those with a medium aneurysm (4.5 to 5.4 cm), a repeat scan at three months. Men with large aneurysms (5.5 cm or more) are referred to vascular surgery.

The UK National Screening Committee (NSC) that reviews evidence to support the implementation, continuation or cessation of screening programmes, is currently considering programme modification to include surveillance for men with sub-aneurysmal aorta (2.5 to 2.9 cm).

AAA screening is not offered for women. No prior UK NSC evidence review on the topic is available, and it is not currently under review.

What are the implications?

Screening is expected to exceed cost-effective thresholds in any scenario. Between a third and a half of AAAs detected by screening would have remained asymptomatic without the hypothetical screening programme, and this rate appears high.

The uncertainties in some model inputs suggest a need for caution in interpretation. For example, more accurate estimates of prevalence and aneurysm size are called for.

This study provides much-needed analysis in this area. Overall it lends support to the current position not to offer AAA population screening for women, but there may be certain groups for whom screening still makes sense.

Citation and Funding

Sweeting MJ, Masconi KL, Jones E et al. Analysis of clinical benefit, harms, and cost-effectiveness of screening women for abdominal aortic aneurysm. Lancet. 2018;392:487-95.

This project was funded by the National Institute for Health Research Health Services and Delivery Research programme (project number 14/179/01).

Bibliography

Anjum A, Powell JT. Is the incidence of abdominal aortic aneurysm declining in the 21st century? Mortality and hospital admissions for England & Wales and Scotland. European Journal of Vascular and Endovascular Surgery. 2012;43(2):161-6.

British Society of Interventional Radiology. Aortic aneurysms. London: British Society of Interventional Radiology; 2018.

Cosford PA, Leng GC, Thomas J. Screening for abdominal aortic aneurysm. Cochrane Database Syst Rev. 2007;2(2):CD002945.

Metcalfe D, Holt PJ, Thompson MM. The management of abdominal aortic aneurysms. BMJ. 2011;342:d1384.

Public Health England. Abdominal aortic aneurysm screening: care pathway. London: Public Health England; 2015.

Thompson S G, Bown M J, Glover M J et al. Screening women aged 65 years or over for abdominal aortic aneurysm: a modelling study and health economic evaluation. Health Technol Assess. 2018;22(43).

UK NSC.  The UK NSC recommendation on abdominal aortic aneurysm screening in men over 65. London: UK National Screening Committee; 2017.

Why was this study needed?

Abdominal aortic aneurysm (AAA) is typically defined as widening of the abdominal aorta to a diameter of 3cm or more. It is about three times more common in men than women. The British Society of Interventional Radiology reports that, in England, 4% of men aged 65-74 (about 80,000) have AAA, resulting in around 6,000 deaths each year. If an aneurysm ruptures, mortality is greater than 80%. Because of this older men are screened so that if an aneurysm is detected with a diameter 5.5 cm or more elective surgical repair can be performed.

Screening also carries potential drawbacks. Treatment carries a risk of mortality, although this should be below 5%, and there are psychological effects of detecting aneurysms below the treatment threshold.

In men, the balance of evidence weighs towards more benefits than harms of screening. In women, the evidence has been less clear.

What did this study do?

This was a decision model analysing the health outcomes and cost-effectiveness of population-based AAA screening for women compared with no screening. Information such as aneurysm prevalence, growth rates, operative mortality and quality of life, came from systematic literature reviews, clinical trials, hospital datasets and registry data. NHS costs included those for invitation, screening, and consultation, elective and emergency surgery.

The baseline model used the same screening pathway as currently used for men. A total of 12 different screening scenarios were tested, increasing the age at screening or thresholds for diagnosis or elective surgery, to derive the most cost-effective option.

Simulation studies are valuable when running a screening trial would require a large sample size and follow-up, and may result in patient harms. However, assumptions in the model may be based on inaccurate or uncertain data.

What did it find?

  • In this model, using the same criteria as for UK men, screening increased detection among women aged 65-95 by 23% compared with no screening (an additional 2,168 cases per million). It resulted in an additional 452 elective operations per 1 million women screened (a 21% increase). However, 33% of screen-detected AAAs would not have been otherwise detected or ruptured during the woman’s lifetime (over-diagnosis). Meanwhile, 13% of those repaired wouldn't have led to death or surgery in the absence of screening (over-treatment).
  • In this model, there were 257 fewer AAA-related deaths per million women (3% decrease). However, for every four women who avoided AAA-related death because of successful screening, one woman died due to elective surgical repair. Overall, 3,900 women need screening to prevent one AAA-related death.
  • The best alternative strategy modelled – screening at age 70 years with lower thresholds for diagnosis (2.5cm) and surgical referral (5.0cm) – gave a 66% increase in AAA detection (9,089 per million). There were an additional 1,301 elective operations per million women (55% increase). However, the rate of over-diagnosis increased to 55% and the rate of over-treatment to 24%.
  • This strategy resulted in 566 fewer AAA-related deaths per million women (8% decrease). However, for every seven women who avoided AAA-related death because of successful screening, two died due to elective surgical repair. Overall, 1,800 women need screening to prevent one AAA-related death.
  • Using the same screening criteria as for UK men, inviting women to screening gave an additional 0.0011 quality adjusted life years (QALYs) at the cost of £30,170 (95% confidence interval [CI] £12,238 to £87,002) per QALY gained. The best alternative strategy in the model gave 0.0020 QALY gain at an additional cost of £22,540 (95% CI £9,522 to £70,638) per QALY gained.

What does current guidance say on this issue?

Public Health England offers AAA screening to men aged 65 years. Normal aortas (less than 3 cm diameter) require no further scans. Men with a small aneurysm (3.0 to 4.4 cm) are given a repeat scan at 12 months and those with a medium aneurysm (4.5 to 5.4 cm), a repeat scan at three months. Men with large aneurysms (5.5 cm or more) are referred to vascular surgery.

The UK National Screening Committee (NSC) that reviews evidence to support the implementation, continuation or cessation of screening programmes, is currently considering programme modification to include surveillance for men with sub-aneurysmal aorta (2.5 to 2.9 cm).

AAA screening is not offered for women. No prior UK NSC evidence review on the topic is available, and it is not currently under review.

What are the implications?

Screening is expected to exceed cost-effective thresholds in any scenario. Between a third and a half of AAAs detected by screening would have remained asymptomatic without the hypothetical screening programme, and this rate appears high.

The uncertainties in some model inputs suggest a need for caution in interpretation. For example, more accurate estimates of prevalence and aneurysm size are called for.

This study provides much-needed analysis in this area. Overall it lends support to the current position not to offer AAA population screening for women, but there may be certain groups for whom screening still makes sense.

Citation and Funding

Sweeting MJ, Masconi KL, Jones E et al. Analysis of clinical benefit, harms, and cost-effectiveness of screening women for abdominal aortic aneurysm. Lancet. 2018;392:487-95.

This project was funded by the National Institute for Health Research Health Services and Delivery Research programme (project number 14/179/01).

Bibliography

Anjum A, Powell JT. Is the incidence of abdominal aortic aneurysm declining in the 21st century? Mortality and hospital admissions for England & Wales and Scotland. European Journal of Vascular and Endovascular Surgery. 2012;43(2):161-6.

British Society of Interventional Radiology. Aortic aneurysms. London: British Society of Interventional Radiology; 2018.

Cosford PA, Leng GC, Thomas J. Screening for abdominal aortic aneurysm. Cochrane Database Syst Rev. 2007;2(2):CD002945.

Metcalfe D, Holt PJ, Thompson MM. The management of abdominal aortic aneurysms. BMJ. 2011;342:d1384.

Public Health England. Abdominal aortic aneurysm screening: care pathway. London: Public Health England; 2015.

Thompson S G, Bown M J, Glover M J et al. Screening women aged 65 years or over for abdominal aortic aneurysm: a modelling study and health economic evaluation. Health Technol Assess. 2018;22(43).

UK NSC.  The UK NSC recommendation on abdominal aortic aneurysm screening in men over 65. London: UK National Screening Committee; 2017.

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

Published on 26 July 2018

Sweeting MJ, Masconi KL, Jones E, Ulug P, Glover MJ, Michaels JA, Bown MJ, Powell JT, Thompson SG

The Lancet Volume 392 , 2018

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.

Expert commentary

Abdominal aortic aneurysm (AAA) has been regarded as a predominantly male disease and, in the UK, only males are screened to reduce the risk of death from rupture. Meanwhile, significant numbers of UK females die from ruptured AAA.

Using what data we have and some mathematical ‘smoke and mirrors’, this paper looks at the value of screening for aneurysms in UK women. The conclusion that we should not introduce screening for AAA in women seems sound. But to be really sure, they suggest we need more information to feed into their model. In effect, it has informed the debate but has not answered the question.

Harvey Chant, Consultant Vascular Surgeon, Royal Cornwall Hospital

The commentator declares no conflicting interests.

Expert commentary

Aneurysm screening for men is clinically and cost-effective. Despite the lower prevalence of aneurysm in women, rupture rates are higher than for men. Complex modelling solutions confirm, however, that population screening in women cannot be justified on either a cost-effective or clinical basis.

Questions remain: what is the prevalence of aneurysms in older women? Are there gender-specific quality of life metrics for screening that might influence screening in targeted groups? A group of women who should be screened (not discussed by the authors) are those who have a blood relative with an aneurysm, because of the genetic predisposition for the condition.

Frank CT Smith, Professor of Vascular Surgery & Surgical Education, University of Bristol

The commentator declares no conflicting interests