01Role and principlesWho benefits and the main preventive aims.
An abdominal aortic aneurysm is a permanent pathological dilatation of the abdominal aorta. In the NHS AAA Screening Programme in England, the operational definition is a maximum anterior-posterior diameter of at least 3.0 cm measured by ultrasound from inner wall to inner wall. Most screen-detected aneurysms are asymptomatic. Screening aims to find aneurysms before rupture, arrange surveillance when small or medium, and refer large or rapidly growing aneurysms for specialist assessment.
Population screening and diagnostic case-finding are different routes. England routinely invites the eligible male cohort during the screening year in which they turn 65; an older unscreened man may self-refer. Someone with symptoms, an abnormal abdominal examination, or an incidental aneurysm on another scan needs ordinary clinical assessment and referral rather than a screening appointment. NICE advises aortic ultrasound when asymptomatic AAA is suspected outside the programme, including when a pulsatile abdominal mass is found.
Risk is strongly associated with age, male sex assigned at birth, current or previous smoking, family history, hypertension, hyperlipidaemia, COPD, and established coronary, cerebrovascular or peripheral arterial disease. NICE advises discussing self-referral with unscreened men aged 66 or older, especially when these factors are present. It also says to consider aortic ultrasound for women aged 70 or older with one or more listed risk factors if AAA has not already been excluded on abdominal imaging. This is selective diagnostic imaging, not routine population screening of women.
Key points
- England invites men during the screening year in which they turn 65.
- Men older than 65 who were never screened may self-refer to their local programme.
- Screening ultrasound records maximum anterior-posterior diameter inner wall to inner wall.
- An aorta under 3.0 cm is screen-negative; 3.0 cm or more is an AAA.
- Women and younger men with risk factors need clinical assessment, not routine programme entry.
- A diagnostic AAA of 5.5 cm or more needs vascular review within two weeks.
- A diagnostic AAA from 3.0 to 5.4 cm needs vascular review within twelve weeks.
- New pain or collapse bypasses screening and activates the emergency symptomatic AAA pathway.
02Assessment and patient selectionRisk features, eligibility and important cautions.
Men resident in England are offered one ultrasound during the screening year in which they turn 65.
A man older than 65 who has never been screened can contact his local AAA screening service directly.
Previous or current smoking, vascular disease, hypertension, hyperlipidaemia, COPD and family history increase suspicion.
For women aged 70 or older with listed risk factors, consider diagnostic aortic ultrasound when prior imaging has not excluded AAA.
New abdominal or back pain, collapse or loss of consciousness requires immediate emergency assessment rather than screening.
03Baseline assessmentMeasurements that guide the plan and track progress.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Screening abdominal ultrasoundFirst step - Why
- Measure the infrarenal aorta without radiation or contrast
- Interpretation and limitations
- The England programme defines AAA at 3.0 cm or more using maximum AP inner-to-inner diameter; under 3.0 cm closes the screening episode.
- 02
Diagnostic aortic ultrasound - Why
- Assess suspected asymptomatic AAA outside population screening
- Interpretation and limitations
- Use maximum AP inner-to-inner measurement and document extra dimensions; refer by diameter even if the person feels well.
- 03
Review of prior abdominal imaging - Why
- Determine whether AAA has already been excluded or detected
- Interpretation and limitations
- A documented adequate study may prevent duplicate screening, while an incidental aneurysm starts a diagnostic vascular pathway.
- 04
CT angiography - Why
- Define morphology when elective repair is being evaluated
- Interpretation and limitations
- Thin-slice arterial-phase CT maps neck, branches and access vessels; CT diameters are not interchangeable with programme ultrasound thresholds.
- 05
Immediate bedside aortic ultrasound - Why
- Detect an aneurysm during a symptomatic emergency presentation
- Interpretation and limitations
- A positive, unavailable or non-diagnostic scan with persisting suspicion requires immediate regional vascular discussion, not delayed screening.
04InterventionsLifestyle, treatment and escalation options.
01Screening routeRoutine invitation and resultFirst stepAn eligible man reaches the England screening cohort+
- 1Offer informed choice and perform the single programme ultrasound appointment.
- 2Record maximum AP inner-to-inner measurements in longitudinal and transverse planes.
- 3Discharge a screen-negative result below 3.0 cm from programme surveillance.
- 4Enter aneurysms from 3.0 to 5.4 cm into programme surveillance and refer qualifying large or rapidly growing aneurysms.
02Diagnostic routeRisk-based clinical assessmentThe person is outside routine screening but AAA is clinically suspected+
- 1Check symptoms, prior imaging, smoking, family history and vascular comorbidity.
- 2Arrange diagnostic aortic ultrasound when asymptomatic AAA remains a possibility.
- 3Refer 3.0 to 5.4 cm AAA for regional vascular review within twelve weeks.
- 4Refer AAA at least 5.5 cm for regional vascular review within two weeks.
03Emergency routePain or collapseNew abdominal or back pain raises concern for symptomatic AAA+
- 1Start immediate clinical resuscitation while requesting bedside aortic ultrasound.
- 2Discuss immediately with the regional vascular service if AAA is shown.
- 3Also discuss immediately when imaging is unavailable or non-diagnostic but suspicion persists.
05Targets, monitoring and follow-upResponse, safety and longer-term review.
- Record whether the person entered through population screening or diagnostic assessment.
- Use the same ultrasound calliper convention when comparing serial diameters.
- Confirm that every positive diagnostic study has a tracked vascular referral.
- Document smoking status, blood pressure and cardiovascular prevention needs after diagnosis.
- Safety-net all known AAA patients about urgent action for new abdominal or back pain.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Sex and registration
Programme eligibility follows male sex assigned at birth; trans women and non-binary people assigned male at birth may need to contact the service if GP registration does not trigger an invitation.
Measurement discipline
Screening uses two maximum AP inner-to-inner measurements, one longitudinal and one transverse, recorded to one decimal place; oblique callipers can falsely enlarge the result.
Incidental means diagnostic
An aneurysm reported on CT, MRI or unrelated ultrasound should remain under a vascular diagnostic pathway and should not be redirected into the screening programme for surveillance.
European guidance scope
ESVS 2024 recommends ultrasound screening in locally defined high-risk populations, but England eligibility and implementation are governed by the NHS programme and NICE.
Diameter modality gap
CT commonly gives a larger measurement than ultrasound because plane and calliper conventions differ; eligibility for repair in NICE is expressed using inner-to-inner maximum AP ultrasound diameter.
07Common pitfallsFrequent interpretation and management errors.
- 01
Sending a symptomatic patient to routine screening dangerously delays vascular assessment.
- 02
Assuming all women are low risk misses NICE selective ultrasound advice for women aged 70 or older.
- 03
Using outer-to-outer or transverse CT diameter against an inner-to-inner ultrasound threshold creates false growth.
- 04
Treating a single negative programme scan as proof against every future symptomatic presentation is unsafe.
- 05
Referring an incidental AAA back into screening confuses responsibility and can open a follow-up gap.