Coronary Artery Calcium Score

Authored by , Reviewed by Dr Adrian Bonsall | Last edited | Meets Patient’s editorial guidelines

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Coronary artery disease is still a leading cause of morbidity and mortality worldwide. Many acute cardiac events occur in previously asymptomatic individuals. There has been much interest in developing screening methods to identify those at risk of having a primary cardiac event. The coronary artery calcium score (CACS) is considered one such tool and is also used in some cases in the investigation of chest pain.

What is coronary artery calcium (CAC)?

The presence of calcium in coronary arteries is almost always indicative of atherosclerotic plaque (but bears no relationship to plaque stability or instability).[1]Atherosclerotic areas, however, do not always contain calcification.

Cardiac risk factors and insulin resistance lead to progression of coronary artery calcification.

How do we measure the coronary artery calcium score (CACS)?

CACS is determined by CT scanning which is non-invasive and can be of two types:

  • Electron beam CT scan (EBCT).
  • Multidetector CT scan (MDCT).

EBCT was used for much of the original research but has been increasingly replaced with MDCT.

The amount of calcium detected in the coronary arteries is converted to a calcium score which correlates with the severity of the atherosclerosis. The score used is the Agatston score, which is calculated from weighted density and area of the calcification identified. Scores are then used to define severity as follows:[2, 3]

Coronary artery calcium scoreCalcification grade = risk of imminent coronary event
>1000Very severe

The main benefit of CACS is its high negative predictive value, reported to be 95-99%.[5]Nothing but atherosclerosis results in calcium in coronary arteries, so its presence is diagnostic. Risk assessment using CACS has been shown to motivate individuals to make lifestyle changes and adhere to medication.[6] CACS predicts cardiac risk independently of established risk scoring systems such as the Framingham score.

Problems with CACS as a screening test include:

  • Not all atherosclerotic plaques contain calcium. Obstructive coronary artery disease is possible with a CASC of 0.[7]
  • CAC scanning is not useful in those at very low or very high risk, or in those with known coronary artery disease.
  • It has not yet been established how often it should be repeated (for example, how long the reassurance of a score of 0 lasts).
  • CACS does not predict functional capacity or the degree of stenosis.

It is unclear at present as to the most appropriate use of CAC scanning but the following are possibilities:

  • Screening asymptomatic individuals with intermediate risk of coronary artery disease (ie Framingham risk score of 10-20% over 10 years). This is the recommendation in American guidelines from the American College of Cardiology Foundation/American Heart Association (ACCA/AHA), along with a lower-classed recommendation for use in those with a 6-10% risk.[8]
  • Risk prediction in those with type 2 diabetes. A meta-analysis published in 2013 found a CACS of 10 or more to be predictive of all-cause mortality as well as cardiovascular events in people with type 2 diabetes.[9]
  • Reclassification of risk when used together with other risk factors.[10]
  • Screening individuals with a strong family history of premature coronary artery disease.

Individuals who have had CAC testing with private screening companies represent a challenge to GPs presented with the results, as there are no guidelines. A non-zero score should prompt at the very least an assessment of all risk factors, and consideration of risk modification strategies (lifestyle changes, blood pressure control, statin, consideration of aspirin etc). Cardiological referral for consideration of further investigation such as stress testing may be required.

Guidelines from the National Institute for Health and Care Excellence (NICE) for assessment and diagnosis of recent-onset chest pain advise measurement of CAC in people in whom stable angina cannot be diagnosed or excluded by clinical assessment alone and who have an estimated likelihood of CAD of 10-29%. (This percentage is based on age, sex and typicality of symptoms and is set out in table form in the guideline.) If the calcium score is zero, other causes of chest pain are likely. NICE recommends decisions about further invasive or non-invasive coronary angiography then be based on whether the CACS is below or above 400.

Further evidence and guidance is required to determine how to use CAC scans effectively and the role they play amongst other cardiac investigations.

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Further reading and references

  • Shah NR, Coulter SA; An evidence-based guide for coronary calcium scoring in asymptomatic patients without coronary heart disease. Tex Heart Inst J. 201239(2):240-2.

  • Youssef G, Budoff MJ; Coronary artery calcium scoring, what is answered and what questions remain. Cardiovasc Diagn Ther. 2012 Jun2(2):94-105. doi: 10.3978/j.issn.2223-3652.2012.06.04.

  1. European guidelines on cardiovascular disease prevention in clinical practice; European Society of Cardiology (2012)

  2. Azevedo CF, Rochitte CE, Lima JA; Coronary artery calcium score and coronary computed tomographic angiography for cardiovascular risk stratification. Arq Bras Cardiol. 2012 Jun98(6):559-68.

  3. Rotterdam Coronary Artery Algorithm Evaluation Framework

  4. Grayburn PA; Interpreting the coronary-artery calcium score. N Engl J Med. 2012 Jan 26366(4):294-6.

  5. Shah NR, Coulter SA; An evidence-based guide for coronary calcium scoring in asymptomatic patients without coronary heart disease. Tex Heart Inst J. 201239(2):240-2.

  6. Youssef G, Kalia N, Darabian S, et al; Coronary calcium: new insights, recent data, and clinical role. Curr Cardiol Rep. 2013 Jan15(1):325. doi: 10.1007/s11886-012-0325-3.

  7. Villines TC, Hulten EA, Shaw LJ, et al; Prevalence and severity of coronary artery disease and adverse events among symptomatic patients with coronary artery calcification scores of zero undergoing coronary computed tomography angiography: results from the CONFIRM (Coronary CT Angiography Evaluation for Clinical Outcomes: An International Multicenter) registry. J Am Coll Cardiol. 2011 Dec 658(24):2533-40. doi: 10.1016/j.jacc.2011.10.851. Epub 2011 Nov 9.

  8. Guideline for Assessment of Cardiovascular Risk in Asymptomatic Adults - Executive Summary; American College of Cardiology Foundation/American Heart Association (ACCF/AHA) Task Force on Practice Guidelines, 2010

  9. Kramer CK, Zinman B, Gross JL, et al; Coronary artery calcium score prediction of all cause mortality and cardiovascular events in people with type 2 diabetes: systematic review and meta-analysis. BMJ. 2013 Mar 25346:f1654. doi: 10.1136/bmj.f1654.

  10. Risk Score Calculator; The Multi-Ethnic Study of Atherosclerosis (MESA)

  11. Chest pain of recent onset; NICE Clinical Guideline (March 2010, updated Nov 2016)