AAA Screening: Benefits, Risks and What the Evidence Shows
In summary - 2-3 minute read
At 65, men in England are offered a one-off ultrasound scan to look for an abdominal aortic aneurysm, or AAA — an enlargement of the main artery through the abdomen.
What is the potential benefit?
Most AAAs cause no symptoms before they become dangerous.
Screening can find an aneurysm before it ruptures, allowing it to be monitored and, if necessary, repaired in a planned operation.
Randomized trials found fewer ruptures and fewer AAA deaths among men invited for screening.
That is the principal benefit.
What is the downside?
Finding an AAA does not mean it would eventually have harmed you.
Many detected aneurysms remain small or grow slowly. Some men will die of something else without their aneurysm ever causing a problem.
Screening can therefore lead to years of surveillance and, in some cases, major surgery for an aneurysm that would never otherwise have caused harm.
The main UK trial showed that screening substantially increased the total number of AAA operations, not merely that it replaced emergency operations with planned ones.
What actually happens if you have the scan?
The test itself is a short, non-invasive ultrasound scan of the abdomen. There is no radiation.
If the aorta measures below 3 cm, the NHS classifies the result as normal and you are normally discharged from the screening programme.
If an AAA is found:
a small aneurysm is usually scanned once a year;
a medium aneurysm is usually scanned every three months;
at 5.5 cm or above, or if it grows rapidly or causes symptoms, you are referred to a vascular specialist to discuss treatment.
Planned surgery is much safer than facing a rupture, but it is still major surgery and carries a risk of serious complications and death.
How large is the benefit today?
This is less certain than the historical trial evidence might suggest.
When the main UK trial began in the late 1990s, an AAA was found in about 5% of men screened.
Today, the English programme finds one in about 0.7% of screened men.
There has not been an equivalent modern randomized trial.
The NHS therefore estimates today's benefit using a computer model combining the old trial evidence with newer data.
Its current estimate is roughly:
one AAA death prevented for every 1,100 men invited for screening over their remaining lifetimes.
That is a modelled estimate, not an outcome directly observed in a modern randomized trial.
Does your individual risk matter?
Very much.
AAA risk is substantially higher in men who smoke, higher in former smokers than never-smokers, and also varies with age, family history and vascular disease.
So the average benefit for all men invited at 65 is not necessarily a good estimate of the benefit for any particular man.
We look at those differences below.
Is this the only way to screen?
No.
England invites all men at 65, but other countries use more risk-based approaches. Men in England who have never previously been screened can also request screening later.
We look at those alternatives below.
One other thing worth knowing
The NHS invitation is designed to encourage men to attend.
Later we look separately at how that choice is presented, and whether the programme measures understanding as closely as it measures uptake.
Show me the evidence
How do we know screening reduces AAA deaths?
The strongest evidence comes from randomized trials.
The largest was the UK Multicentre Aneurysm Screening Study, or MASS, involving nearly 68,000 men aged 65–74.
After about 13 years there had been:
224 AAA-related deaths among men invited for screening, compared with 381 among men who were not invited.
There were also 273 ruptures in the invited group compared with 476 in the control group.
Expressed more intuitively, for every 10,000 men invited there were approximately:
66 AAA deaths among men invited for screening
versus
112 among men not invited.
That is about 46 fewer AAA deaths per 10,000 men invited over 13 years.
In MASS, that was equivalent to about 216 men invited for screening for every one AAA death prevented over 13 years.
This was observed in a randomized trial. It was not produced by a computer model.
The important qualification is that these were men recruited more than 25 years ago, when AAA was considerably more common than it is among men entering the programme today.
How much extra surgery did screening cause?
This is an important part of the trade-off.
Over 13 years, MASS found:
| AAA operations | Invited for screening | Not invited |
|---|---|---|
| Planned operations | 600 | 277 |
| Emergency operations | 80 | 166 |
| Total operations | 680 | 443 |
Screening therefore produced 323 more planned operations, while there were 86 fewer emergency operations.
Overall, there were 237 more AAA operations in the screening group.
That tells us something important.
Screening did not simply identify the same aneurysms earlier and turn emergency operations into planned ones. It increased the total amount of surgery substantially.
Some of those additional operations prevented later rupture. That is part of how screening saves lives.
But some will have treated aneurysms that would never have caused harm.
The trial cannot tell us which individual operations belonged to which category.
Why does planned surgery still matter?
Because a planned repair is much safer than a rupture.
The NHS leaflet says roughly 1 in 67 people undergoing planned AAA surgery die as a result.
It also says around 85 in 100 people whose aneurysm ruptures die.
Those figures do not have identical denominators — the rupture figure includes people who never reach surgery — so they should not be compared as though they were equivalent surgical mortality rates.
But they explain the fundamental rationale for screening:
if an aneurysm is going to rupture, finding and treating it beforehand is far preferable to discovering it as an emergency.
The difficult part is identifying which detected aneurysms would actually ever have reached that point.
How much overdiagnosis is there?
Overdiagnosis does not mean the scan was wrong.
It means finding a real aneurysm that would never have caused symptoms, ruptured or shortened the man's life had it remained undiscovered.
A later analysis of the MASS data estimated that, for every 10,000 men invited for screening, around 176 would be overdiagnosed, 37 would undergo potentially avoidable preventive surgery, and about 1.6 would die as a consequence of that surgery.
These are estimates derived from the historical trial data, not outcomes that can be identified directly in individual men, and the methodology has been debated.
But the underlying point is clear:
Screening finds some aneurysms that would never otherwise have harmed the men carrying them.
That may mean years of surveillance. For some men it may eventually mean an operation they would never otherwise have undergone.
Why might the benefit be smaller today?
AAA is now much less common than it was in MASS.
In MASS, about 4.9% of men who attended screening had an AAA detected. In the current English programme, the figure is about 0.7%.
That matters because a lower underlying prevalence means fewer men can benefit from screening.
MASS reported that about 216 men had to be invited for screening to prevent one AAA death over 13 years. The current NHS model estimates a much smaller absolute benefit: roughly 1 in 1,100 over a lifetime.
The historical benefit was directly observed in a randomized trial. The current estimate is modelled.
Finding an AAA is therefore much more common than preventing an AAA death: roughly 1 in 145 screened men currently has an aneurysm detected, while the NHS model estimates about one AAA death prevented per 1,100 men invited.
How does the NHS estimate today's benefit?
There has not been another large modern randomized English trial.
Instead, the contemporary assessment uses a computer simulation combining the historical trial evidence with newer information about AAA prevalence, treatment, survival and other factors.
The model then estimates what would happen over the remaining lifetimes of men invited for screening compared with men who were not invited.
The current estimate therefore depends partly on assumptions about what would happen without screening — something the present programme cannot directly observe.
How much does smoking change your risk?
Quite substantially.
A recent study of more than 16,000 men screened at age 65 found that AAA was concentrated heavily among current and former smokers.
Using the study's reported smoking groups, the approximate prevalence was:
| Smoking history | Approximate AAA prevalence in the study |
|---|---|
| Never smoked | ~0.5% — about 1 in 200 |
| Former smoker | ~1.7% — about 1 in 60 |
| Current smoker | ~3% — about 1 in 30 |
These are approximate calculations from that study's data, not current English risk estimates.
The study population had an overall AAA prevalence of about 1.5%, compared with about 0.7% in the current English programme.
So the exact percentages should not simply be transferred to an English man today.
What the study shows convincingly is the size of the difference associated with smoking history.
The same study found that restricting screening to men who had ever smoked would have identified about 85% of the AAAs while screening about 61% of the men.
Family history, age and established vascular disease also affect risk.
And one distinction is particularly important:
your chance of having an AAA detectable on ultrasound is not the same as your chance of ever dying from it.
Are there alternatives to screening every man at 65?
Yes.
England invites all men at 65.
The US takes a more risk-based approach: routine one-off screening is recommended for men aged 65–75 who have ever smoked, while never-smokers are considered selectively according to other risk factors and preferences.
It shows that the evidence can support different screening strategies.
The policy question is therefore broader than:
Does AAA screening work?
It is also:
Which men should be screened, and at what age?
That question becomes more important as AAA becomes less common and the differences between high- and low-risk men become larger in relative importance.
Could you choose to be screened later?
Yes.
Men over 65 in England who have never previously been screened can request NHS AAA screening later.
There is no evidence here that waiting is better; the practical point is simply that the invitation at 65 is not necessarily now or never.
Notice the Nudge
The screening evidence and the way the invitation is presented are two separate questions.
The NHS invitation arrives with an appointment already booked.
The letter says:
“Your GP surgery recommends that all men take up the offer of AAA screening.”
That is a general endorsement of the programme. It does not mean that your own GP has reviewed your individual risk and personally recommended the scan.
The leaflet also tells you that most men attend and highlights the striking statistic that approximately 85 out of 100 people whose aneurysm ruptures die.
The appointment is already booked. The letter carries the endorsement of your GP surgery. It tells you that most men attend. And it highlights the very high fatality rate after rupture. Together, those features steer the reader towards attending.
None of those statements is necessarily wrong, but together they clearly steer the reader towards attending.
The programme also has formal uptake targets and uses reminders, text messages and GP endorsement to encourage attendance.
At the same time, NHS screening policy says that men should be able to make an informed choice, including choosing not to participate.
That creates an interesting asymmetry.
The programme has detailed national measures of offer, coverage, uptake and surveillance attendance.
We did not find a corresponding national performance measure of whether men understand:
their absolute chance of benefiting;
the possibility of overdiagnosis;
the additional surgery created by screening;
or the fact that today's estimate of benefit depends substantially on modelling.
It shows what the programme measures most closely.
And for someone receiving an invitation, that is useful context.
Sources and calculations
The figures in this article come from randomized trials, current NHS programme data, published modelling and screening-policy documents.
Where we have converted published data into percentages, “1 in X” figures or rates per 10,000, we identify those as our calculation.
MASS randomized trial
The main historical source is the Multicentre Aneurysm Screening Study (MASS), the largest UK randomized trial of AAA screening.
At 13 years it reported:
224 AAA-related deaths among men invited for screening versus 381 among controls
273 ruptures versus 476
600 elective AAA operations versus 277
80 emergency AAA operations versus 166
Source: Thompson SG et al. Final follow-up of the Multicentre Aneurysm Screening Study (MASS) randomized trial of abdominal aortic aneurysm screening. British Journal of Surgery, 2012.
Our calculation:
224 ÷ 33,883 × 10,000 ≈ 66 AAA deaths per 10,000 men invited
381 ÷ 33,887 × 10,000 ≈ 112 per 10,000 men not invited
Difference ≈ 46 fewer AAA deaths per 10,000 men invited over 13 years.
Total operations:
680 in the invited group versus 443 in controls = 237 additional AAA operations overall.
Overdiagnosis
A later analysis of the MASS data estimated around 176 overdiagnosed AAAs per 10,000 men invited, equivalent to roughly 45% of screen-detected aneurysms over the period studied.
It also estimated around 37 potentially avoidable preventive operations per 10,000 men invited.
These are estimates, not directly observable outcomes in individual men, and their methodology and interpretation have been debated.
Source: Johansson M, Hansson A, Brodersen J. Estimating overdiagnosis in screening for abdominal aortic aneurysm. BMJ, 2015.
Current English prevalence
In England in 2024–25:
337,752 men were offered screening
82.3% were conclusively tested
1,907 AAAs were detected
Source: NHS England, Abdominal Aortic Aneurysm Screening Standards Report 2024 to 2025.
Our calculation:
337,752 × 82.3% ≈ 277,970 men screened
1,907 ÷ 277,970 ≈ 0.69%
That is about 7 AAAs per 1,000 men screened, or roughly 1 in 145.
Current modelled benefit
The 2025 UK effectiveness review modelled 300,000 men invited for screening against 300,000 not invited.
The model estimated:
510 more elective repairs
390 fewer ruptures
145 fewer emergency repairs
267 fewer AAA deaths
Source: UK AAA Screening Programmes: 10-year Effectiveness Review, 2025.
Our calculation:
267 ÷ 300,000 = 0.00089
Equivalent to approximately:
1 AAA death prevented per 1,124 men invited
which we round to about 1 in 1,100.
This is a modelled lifetime estimate, not a contemporary randomized-trial result.
Smoking and targeted screening
We used:
Söderberg P, Wanhainen A, Svensjö S.
Optimising Abdominal Aortic Aneurysm Screening of 65 Year Old Men by Exploring Risk Factor Based Targeted Screening Strategies in the Light of Declining Prevalence of the Disease. European Journal of Vascular and Endovascular Surgery, 2025.
The study screened 16,232 men aged 65 and found 236 AAAs.
Using the reported group data, the approximate AAA prevalence was:
never-smokers: ~0.5%
former smokers: ~1.7%
current smokers: ~3.1%
These are our approximate calculations from the study data, not current English prevalence estimates.
The study also reported that screening men who had ever smoked would have identified about 85% of the AAAs while screening about 61% of the men.
Alternative screening policy
For the US comparison we used the US Preventive Services Task Force recommendation on AAA screening.
It recommends one-time screening routinely for men aged 65–75 who have ever smoked, and selective screening for never-smokers in that age group.
Source: US Preventive Services Task Force, Abdominal Aortic Aneurysm: Screening.
NHS invitation, uptake and informed choice
For the discussion of the invitation and programme design we used:
NHS AAA Screening Programme standards
AAA screening standard operating procedures
NHS guidance on reducing screening inequalities
NHS guidance on informed choice and screening information
the current AAA invitation leaflet
These documents show that the programme measures uptake and uses mechanisms including pre-booked appointments, reminders and GP endorsement to encourage attendance.
We found no equivalent national performance measure testing whether men understand absolute benefit, overdiagnosis, additional surgery or the modelling behind the contemporary benefit estimate.
Screening after age 65
NHS guidance states that men over 65 who have not previously been screened can request AAA screening later.
That is the basis for our statement that declining the routine invitation at 65 does not necessarily mean permanently losing access to screening.
Check us
If a number comes from a randomized trial, we say so.
If it comes from a model, we call it modelled.
If we calculate it ourselves, we label it our calculation.
If a figure is uncertain or disputed, we say that too.
Don’t trust the NHS because it is the NHS. Don’t trust us because we wrote this article. Check the evidence.