GPAtlas🧭 When to offer screening (and when to suspect AAA)
An abdominal aortic aneurysm is a focal dilatation of the abdominal aorta to ≥ 3 cm, or to at least 1.5× its normal diameter. The infrarenal segment is involved in the majority of cases, and most aneurysms are entirely asymptomatic – usually detected through screening or found incidentally on imaging requested for another reason.
The clinical importance lies in rupture: there is a long, silent period of growth before an AAA bursts, and once it does the internal bleeding is frequently fatal – up to half of those reaching hospital for emergency repair do not survive to discharge. This long pre-symptomatic window is precisely why population screening works. The NHS AAA Screening Programme offers a single, painless abdominal ultrasound to men in the year they turn 65.
The key clinical skill in primary care is twofold: risk-stratify by maximum aortic diameter, and never miss a rupture. Management is driven almost entirely by size and growth rate.
| Maximum AP diameter | Classification | Action |
|---|---|---|
| < 3.0 cm | Normal | Discharge – no surveillance |
| 3.0–4.4 cm | Small AAA | 12-monthly surveillance |
| 4.5–5.4 cm | Medium AAA | 3-monthly surveillance |
| ≥ 5.5 cm | Large AAA | Refer to vascular service within 2 weeks |
Raise suspicion in men over 65, particularly those with a smoking history (the strongest modifiable risk factor), family history of AAA, hypertension, COPD, or European family origin. Men aged 66 and over who were never screened can self-refer to the programme.
Source: NICE NG156 · NHS AAA Screening Programme
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