AAA screening results: what your aorta size means
An AAA screening ultrasound measures how wide your abdominal aorta is, in centimeters. Under 3.0 cm, no aneurysm is found. At 3.0 cm or more, it is called an abdominal aortic aneurysm, and what happens next depends on the size. Your doctor decides your follow-up. (USPSTF, 2019) (NHS, 2024)
Get help right away for severe, sudden or constant pain in the belly or back (it may spread to the groin, buttocks or legs), passing out, clammy skin, dizziness, nausea and vomiting, or a rapid heart rate. Call 911 or go to the emergency room. (MedlinePlus, 2025)
What the number means
- Under 3.0 cm: no aneurysm. The USPSTF recommends one-time screening, and the UK program says you will not need more scans. (USPSTF, 2019) (NHS, 2024)
- 3.0 cm or more: an abdominal aortic aneurysm. (USPSTF, 2019) The USPSTF says 90% or more of aneurysms found by screening are between 3.0 and 5.5 cm, and the usual care for stable smaller ones is a repeat ultrasound at regular intervals, because the risk of rupture is small. (USPSTF, 2019) UK screening data put that risk at 0.4% a year for aneurysms below 5.5 cm. (NICE NG156, 2020)
Aneurysms often grow slowly over many years with no symptoms. (MedlinePlus, 2025) Growth varies a lot: pooled studies cited by the ACC/AHA found about 1.5 to 2 mm a year at 3.0 to 3.9 cm, and about 3.3 to 5.7 mm a year at 4.0 to 5.9 cm. (ACC/AHA, 2022)
How often the scan is repeated
The USPSTF notes that repeat-scan intervals vary between guideline groups. (USPSTF, 2019) Here are two of them side by side. Your doctor sets your own schedule; for example, the ACC/AHA says shorter intervals are often used for people who smoke or have diabetes. (ACC/AHA, 2022)
| Aneurysm size | ACC/AHA 2022 (US) | NHS AAA screening (UK) |
|---|---|---|
| 3.0 to 3.9 cm | Every 3 years | Every year (small: 3.0 to 4.4 cm) |
| 4.0 to 4.4 cm | Every year | Every year (small) |
| 4.5 to 4.9 cm | Men: every year. Women: every 6 months | Every 3 months (medium: 4.5 to 5.4 cm) |
| 5.0 to 5.4 cm | Every 6 months | Every 3 months (medium) |
| 5.5 cm or more | Rupture risk rises above 5.5 cm in men (above 5.0 cm in women); your doctor discusses next steps | Referred to a vascular surgeon for more tests |
Sources: ACC/AHA 2022 surveillance recommendations (ACC/AHA, 2022) and the NHS results table. (NHS, 2024) In the UK, people with a small or medium aneurysm also see a specialist nurse for advice. (NHS, 2024)
Where the guidelines differ
- How often: for the smallest aneurysms (3.0 to 3.9 cm), the US guideline allows 3 years between scans; the UK program scans every year. For 4.5 to 5.4 cm, the UK program scans every 3 months and the US guideline every 6 to 12 months. (ACC/AHA, 2022) (NHS, 2024)
- When a specialist is involved: NICE (England) says everyone with an aneurysm of 3.0 cm or more should be referred to a regional vascular service: within 12 weeks for 3.0 to 5.4 cm, and within 2 weeks for 5.5 cm or more. (NICE NG156, 2020) The USPSTF says the standard of care is to refer people with an aneurysm of 5.5 cm or more to a surgeon. (USPSTF, 2019)
- How it is measured: the ACC/AHA uses mainly the outer edge to outer edge of the aortic wall; NICE and the UK program use the inner edge to inner edge. NICE says using one consistent method makes results easier to compare over time. (ACC/AHA, 2022) (NICE NG156, 2020)
Where bodies differ: the ACC/AHA says rupture risk rises above 5.5 cm in men and above 5.0 cm in women, and it shortens scan intervals for women at 4.5 cm. (ACC/AHA, 2022) The USPSTF notes that small aneurysms have a higher rupture risk in women, and that one quarter to one third of women whose aneurysm ruptures had one below 5.5 cm. (USPSTF, 2019)
When growth matters
Your doctor compares each scan with the last one. The ACC/AHA calls an aneurysm rapidly growing if it gets 0.5 cm or more larger in 6 months, or 1 cm or more larger in 1 year. (ACC/AHA, 2022) Symptoms can come on quickly if an aneurysm expands fast or leaks. (MedlinePlus, 2025) What to do about any change is a decision for you and your doctor. For general next steps, see after an abnormal screening result.
Questions people ask
What is a normal aorta size on an AAA screening ultrasound?
An abdominal aortic aneurysm is usually defined as an aorta 3.0 centimeters or wider. Below that, no aneurysm is found; in the UK screening program that means no more scans are needed. (USPSTF, 2019) (NHS, 2024)
How often is a small aortic aneurysm checked?
It depends on the size and on which guideline your doctor follows. The 2022 ACC/AHA guideline suggests an ultrasound every 3 years at 3.0 to 3.9 cm; the UK program scans small aneurysms (3.0 to 4.4 cm) every year. Your doctor sets your schedule. (ACC/AHA, 2022) (NHS, 2024)
How fast does an aortic aneurysm grow?
Growth varies a lot from person to person. The ACC/AHA guideline cites pooled studies showing about 1.5 to 2 mm a year for aneurysms of 3.0 to 3.9 cm, and about 3.3 to 5.7 mm a year for 4.0 to 5.9 cm. (ACC/AHA, 2022)
Is the size limit different for women?
Yes, in the US guideline. The ACC/AHA says rupture risk rises above 5.5 cm in men and above 5.0 cm in women, and it shortens scan intervals at smaller sizes for women. The USPSTF notes that small aneurysms have a higher rupture risk in women. (ACC/AHA, 2022) (USPSTF, 2019)
What symptoms mean I should get help right away?
MedlinePlus lists severe, sudden or constant belly or back pain (which may spread to the groin, buttocks or legs), passing out, clammy skin, dizziness, nausea and vomiting, and a rapid heart rate. Call 911 or go to the emergency room. (MedlinePlus, 2025)