About a CT calcium score scan
The coronary arteries supply blood to the heart muscle. In coronary artery disease, fatty deposits called plaque build up in the artery walls over many years, and some of this plaque hardens with calcium. A CT calcium score scan, also called a coronary artery calcium (CAC) scan, is a quick, low-dose CT (computed tomography) scan of the heart that measures how much calcium is in these arteries. No injection is needed.
The result is a number, the calcium score (often called an Agatston score). A score of zero means no calcium was seen, which is linked to a low risk of a heart attack in the next few years. The higher the score, the more plaque there is and the higher the risk. The score is often compared with that of other people of the same age and sex.
A calcium score is most useful for people without symptoms whose risk of heart disease is uncertain, for example when a doctor has estimated your 10-year risk using a risk calculator and it is not clear whether you would benefit from treatment such as a statin. It does not show how narrow the arteries are or detect soft plaque without calcium, so a low score does not completely rule out heart disease. If you have chest pain, a CT coronary angiogram or other heart tests are usually needed instead. You can read more in our article on CT calcium scoring.
This scan requires a referral from a specialist, such as a cardiologist, who will interpret the score alongside your other risk factors and advise on any treatment.
What happens during the scan
Small sticky pads (electrodes) are placed on your chest to record your heartbeat, so the pictures can be timed between beats. You lie on your back on the scanner bed with your arms raised above your head. The bed moves through a short, open ring while your heart is scanned. You will be asked to hold your breath for about 10 seconds. The scan itself takes only a few seconds, and there is no injection.
Is CT safe?
CT uses X-rays, which are a type of ionising radiation. A calcium score scan uses a low-dose technique and covers only the heart, so the dose is lower than for a standard chest CT (about 8 mSv). The risk from a single scan is very small, and every CT scan is checked by a radiologist or radiographer to make sure the benefit of the scan outweighs the risk, as required by the Ionising Radiation (Medical Exposure) Regulations. If you have had other CT scans recently, tell us when you book.
What the scan can show
A CT calcium score scan can help to:
- measure calcium in the coronary arteries
- show whether coronary artery disease is present
- estimate your risk of a heart attack
- help decide whether you would benefit from treatment, such as a statin
When to get urgent help: call 999 if you have chest pain that spreads to your arms, neck, jaw or back, or chest pain with sweating, feeling sick or breathlessness. This could be a heart attack. Do not wait for a scan.
Preparing for your scan
No special preparation is usually needed. Avoid caffeine (tea, coffee, energy drinks and cola) and smoking for a few hours beforehand, as they can speed up your heart rate. Take your normal medicines. Wear a top that is easy to remove, as the pads are placed on your chest. Upload your specialist’s referral letter and any recent cholesterol or blood pressure results when you book.
Wear loose, comfortable clothing without metal zips, poppers or buttons, and leave jewellery at home, as metal in the scan area can affect the pictures. You may be asked to change into a gown. Unlike MRI, CT is not affected by pacemakers or most metal implants, and the scanner is a short open ring rather than a tunnel, so it is usually easier for people who feel anxious in enclosed spaces.
Tell the team before your scan if you are, or might be, pregnant or breastfeeding, if you have kidney problems, diabetes (especially if you take metformin), asthma, thyroid problems or allergies, or if you have had a reaction to contrast dye before. If you need contrast, you may be asked for a recent kidney blood test result.
Frequently asked questions
What does my calcium score mean?
A score of zero means no calcium was found, which is linked to a low risk of a heart attack in the next few years. Higher scores mean more plaque and a higher risk. Your specialist will explain your result alongside your other risk factors.
Is a calcium score the same as a CT coronary angiogram?
No. A calcium score is a quick scan without contrast that measures calcium. A CT coronary angiogram uses contrast to show the inside of the arteries and how narrow they are, and is used for people with chest pain.
Why do I need a specialist referral?
A calcium score is only helpful when it is interpreted alongside your other risk factors, and the result may lead to treatment or further tests. A specialist makes sure the scan is right for you and explains what the score means.
Do I need a referral?
Yes. This scan requires a referral from a specialist, such as a cardiologist. Please upload the referral when you book.
Sources
- RadiologyInfo.org – Cardiac CT for calcium scoring
- British Heart Foundation – Cardiac CT scan
- NHS – Coronary heart disease: diagnosis
- NICE CG95 – Recent-onset chest pain of suspected cardiac origin
- NHS – CT scan
The information on this page has been gathered from various sources and is provided for general information only. It is not medical advice. TOP MRI is not liable for the accuracy or completeness of this information. Please speak to your doctor or the scanning centre about your own situation.