Carotid artery screening: who needs a neck ultrasound, and what the results mean
The carotid arteries are two large blood vessels in your neck that supply your brain and head with blood. In carotid artery disease they become narrow or blocked, usually because of a buildup of plaque made of fat, cholesterol, calcium and other substances. (MedlinePlus, carotid artery disease) The usual test is a carotid duplex ultrasound. (MedlinePlus, carotid duplex)
Stroke and TIA are emergencies. If you or someone else has sudden face drooping, arm weakness or slurred speech, call 911 right away. (MedlinePlus, stroke) Warning signs.
Screening adults without symptoms
The USPSTF recommends against screening for carotid artery narrowing (stenosis) in the general adult population (grade D, 2021). It applies to adults who have never had a stroke and have no signs or symptoms of a transient ischemic attack (TIA, a "mini-stroke"). The USPSTF found that the harms of screening outweigh the benefits, and this matches its 2014 recommendation. (USPSTF, 2021)
If you have no symptoms and are offered a carotid ultrasound, for example as part of a screening package, this recommendation applies to you. For other tests in the same group, see screening tests you may not need.
What the USPSTF found:
- Narrowing is uncommon: it is low in the general population (0.5% to 1%) but increases with age, and it causes a relatively small proportion of strokes. (USPSTF, 2021)
- False positives: duplex ultrasound has reasonable accuracy, but when used to screen the general population it gives many false-positive results. (USPSTF, 2021)
- Follow-up testing has risks: in older studies, 0.4% to 1.2% of people who had angiography to confirm a result had a stroke as a result. Angiography is now less common than MRI or CT angiography. (USPSTF, 2021)
- No proof of benefit: there is too little direct evidence that screening people without symptoms reduces stroke or death. (USPSTF, 2021)
- Risk factors: older age, male sex, high blood pressure, smoking, high cholesterol, diabetes and heart disease raise the risk of narrowing, but there is no validated way to tell who is at higher risk of narrowing, or of stroke when narrowing is present. (USPSTF, 2021)
The USPSTF asks clinicians to stay alert to signs and symptoms of carotid artery narrowing and to check them as appropriate. (USPSTF, 2021)
When doctors order the test
| Situation | What the source says |
|---|---|
| No symptoms, no past stroke or TIA | The USPSTF recommends against screening the general adult population (grade D). (USPSTF, 2021) |
| A stroke or TIA (mini-stroke) | A carotid ultrasound may be ordered. NICE says everyone with a TIA who is considered for carotid surgery after specialist assessment should have urgent carotid imaging. (MedlinePlus, carotid duplex) (NICE NG128) |
| A bruit (whooshing sound) heard over the neck arteries | A carotid ultrasound may be ordered; a bruit may mean the artery is narrowed. (MedlinePlus, carotid duplex) |
| Narrowing found before, or past surgery on the artery | A follow-up carotid ultrasound may be ordered. (MedlinePlus, carotid duplex) |
Carotid artery disease often causes no symptoms until the narrowing or blockage is severe. Signs can include a bruit, a TIA or a stroke. (MedlinePlus, carotid artery disease)
What the ultrasound involves
The test uses sound waves to show how well blood flows through the carotid arteries. It is done in a vascular lab or radiology department. (MedlinePlus, carotid duplex)
- No preparation is needed. (MedlinePlus, carotid duplex)
- You lie on your back with your head supported. The technician puts a water-based gel on your neck and moves a wand (transducer) back and forth over it. (MedlinePlus, carotid duplex)
- You may feel some pressure, which should not hurt, and you may hear a whooshing sound, which is normal. (MedlinePlus, carotid duplex)
- There are no risks with the procedure. (MedlinePlus, carotid duplex)
The test can detect blood clotting, narrowing and other causes of blockage in the carotid arteries. (MedlinePlus, carotid duplex) Other imaging tests for the carotid arteries include MRI (magnetic resonance) angiography and CT angiography. (USPSTF, 2021) For the ultrasound of the aorta in the belly, see AAA ultrasound: what to expect.
How narrowing is reported
- Percent narrowed: the result tells how open or narrowed the arteries are, for example 10%, 50% or 75% narrowed. (MedlinePlus, carotid duplex)
- Normal: no problem with blood flow, and no significant blockage or narrowing. (MedlinePlus, carotid duplex)
- Abnormal: the artery may be narrowed, or something is changing the blood flow. This is a sign of atherosclerosis (plaque buildup) or another blood vessel condition. In general, the more narrowed the artery, the higher the risk for stroke. (MedlinePlus, carotid duplex) Your provider may order more tests, such as MRI angiography, or repeat the scan later. (MedlinePlus, carotid duplex)
- Measuring method: there is more than one way to measure the percent. NICE asks that carotid imaging reports state which criteria were used, ECST (European Carotid Surgery Trial) or NASCET (North American Symptomatic Carotid Endarterectomy Trial). (NICE NG128)
For the aorta scan, see AAA screening results.
Stroke and TIA warning signs
Stroke symptoms often happen quickly: sudden numbness or weakness of the face, arm or leg (especially on one side), sudden confusion or trouble speaking or understanding, sudden trouble seeing in one or both eyes, sudden trouble walking, dizziness or loss of balance, and sudden severe headache with no known cause. (MedlinePlus, stroke)
MedlinePlus uses F.A.S.T. to remember what to look for: (MedlinePlus, stroke)
- Face: drooping on one side when smiling.
- Arm: weakness when the arms are raised, and one arm drifts downward.
- Speech: slurred or strange.
- Time: to call 911.
A TIA has the same symptoms as a stroke but they go away, usually within 1 to 2 hours. A TIA is a medical emergency: call 911 right away and do not ignore symptoms because they go away, as they may warn of a future stroke. (MedlinePlus, TIA) In the UK, the NHS says to call 999 if you have had signs of a stroke in the last 24 hours, even if they have stopped, and not to drive yourself to A&E. (NHS, stroke symptoms) After a TIA, the NHS says you should be referred to see a specialist within 24 hours of the onset of symptoms. (NHS, TIA)
Where they differ:
- Adults without symptoms: the USPSTF recommends against screening (grade D). As summarized by the USPSTF, the American Heart Association and American Stroke Association also recommend against routine duplex ultrasound screening in people without symptoms. (USPSTF, 2021)
- A bruit without symptoms: joint guidelines from several US professional societies say ultrasound is indicated or reasonable for people without symptoms who have a carotid bruit, as summarized by the USPSTF, (USPSTF, 2021) while the USPSTF itself finds that listening for a bruit has poor accuracy. (USPSTF, 2021)
- People with several risk factors: the Society for Vascular Surgery and the same joint guidelines recommend considering ultrasound screening in people with multiple stroke risk factors and in those with known peripheral artery disease or other cardiovascular disease, as summarized by the USPSTF, (USPSTF, 2021) while the USPSTF found no validated way to identify who is at higher risk. (USPSTF, 2021)
- US and UK emergency numbers: 911 in the US (MedlinePlus, stroke) and 999 in the UK. (NHS, stroke symptoms)
Your doctor decides what your result means for you.
This page does not give treatment, medicine or surgery advice. If you have a flagged result, see after an abnormal screening result for questions to ask.
Questions people ask
Should I have a carotid ultrasound if I have no symptoms?
The USPSTF recommends against screening adults who have never had a stroke and have no signs or symptoms of a TIA (grade D, 2021). It found that the harms of screening outweigh the benefits. This applies whether the scan is offered at a checkup or as part of a screening package. (USPSTF, 2021)
Does my doctor listening to my neck count as screening?
The USPSTF found that listening for a carotid bruit has poor accuracy for finding narrowing and does not consider it a reasonable screening approach. If a provider does hear a bruit, MedlinePlus says it may mean the artery is narrowed and a carotid ultrasound may be ordered. (USPSTF, 2021) (MedlinePlus, carotid duplex)
What does "50% narrowed" mean on a carotid ultrasound report?
The result describes how open or narrowed the carotid arteries are, for example 10%, 50% or 75% narrowed. In general, the more narrowed the artery is, the higher the risk for stroke. NICE asks that carotid imaging reports state which measuring method (ECST or NASCET) was used. (MedlinePlus, carotid duplex) (NICE NG128)
Does a carotid ultrasound hurt or need preparation?
No preparation is needed. You may feel some pressure as the probe moves over your neck, but it should not hurt, and you may hear a whooshing sound. MedlinePlus says there are no risks with the test itself. (MedlinePlus, carotid duplex)
What if stroke symptoms go away on their own?
Get help anyway. MedlinePlus says a TIA is a medical emergency and to call 911 even if the symptoms go away. The NHS says to call 999 if you have had signs of a stroke in the last 24 hours, even if they have stopped. (MedlinePlus, TIA) (NHS, stroke symptoms)