CAC score: To test or not to test?

A patient comes in requesting a coronary artery calcium (CAC) score test and has no cardiovascular disease (CVD) symptoms. What is considered best practice?
 
For the large group of people who are at low risk of CVD, they have ‘little or nothing to gain’ from CAC score testing, according to Professor of General Practice Mark Morgan, who is Chair of the RACGP Expert Committee – Quality Care (REC–QC) and First Do No Harm Expert Steering Group.
 
‘In my practice I see people who have heard of the CAC score and think that it might be a good idea,’ he told newsGP.
 
‘Afterall, they say, if there is a test available why would you not do it just to be on the safe side?’
 
Ruling out patients with no CVD symptoms, as well as those who are already known to be at high risk of or have established CVD, there is a small group remaining who may benefit from the test.
 
‘That really leaves just an intermediate risk group where it is difficult to know whether to recommend lifestyle plus preventive medication, and where the results of CAC score will influence the patient’s decision,’ Professor Morgan said.
 
The latest released topic in the RACGP’s First do no harm: A guide to choosing wisely is the GP and accompanying patient resource, ‘Coronary artery calcium scoring in asymptomatic people’, which outlines the ‘traffic light system’ of recommendations for GPs in managing requests for a CAC score.
 
While a CAC score can determine CVD risk by measuring calcium deposits in the coronary arteries as part of atherosclerotic plaques, GPs can use other risk-estimate measures which, according to the RACGP, may be more effective and potentially less harmful, including routine lifestyle assessments.
 
In addition to patients who have high risk or established CVD, CAC scoring is not recommended in the generalised population screening for CVD risk, or to investigate chest pain or other symptoms suggestive of heart disease.
 
‘For people who we know are at high risk of heart disease, there is little point in doing a CAC score because all these people should be offered lifestyle advice and preventive medication in the form of antihypertensives and statins,’ Professor Morgan said.
 
‘Examples of people in this high-risk category include those who have already had some sort of vascular event such as stroke, myocardial infarction or angina.
 
‘Other high-risk patients are those with moderate-to-severe kidney disease, for example people with eGFR <45 or persistent raised urinary albumin to creatine ration: >25 for men, >35 for women.’
 
Using the new Australian CVD risk calculator, Professor Morgan said those assessed with a >10% five-year risk fall into the category of people ‘who don’t gain any advantage’ from having a CAC score.
 
Conversely, a calcium score of zero means that the risk of having a heart attack in the next five years is very low.
 
For asymptomatic patients, the reasons behind the RACGP’s recommendations – which align with current national guidelines – to not routinely conduct CAC score tests are to address over-testing, over-diagnosed and over-treated conditions, interventions with insufficient evidence, and unnecessary costs and wastage.
 
‘The efficacy of CAC scoring in reducing the risk of CVD in asymptomatic people has yet to be determined,’ the First do no harm guide states.
 
‘CAC scoring may have important clinical benefits in some settings, but this has yet to be well demonstrated in clinical trials. In addition, it may have little overall impact on patient health outcomes.’
 
Professor Morgan adds the CAC scoring test is ‘not free of problems’.
 
‘There are costs involved for patients and the test uses a CT scan with attendant cumulative risks of radiation exposure,’ he said.
 
‘Also, from an equity point of view, the potential waste of resources in doing low-value tests impacts the ability of the health system to provide much more important services.
 
‘Every low-value test adds to greenhouse gases and increases the carbon footprint of healthcare.’
 
The RACGP states that ‘a false sense of security’ may also come with the test, because a low CAC score is no guarantee for never having cardiovascular issues during a lifetime, and should only be done if the results will help with shared decision making, such as whether long-term medication is needed.
 
The latest GP/patient resource in the First do no harm guide provides succinct information for GPs and a parallel version of the information in plain language for patients, Professor Morgan said.
 
‘It’s a great resource to help GPs have respectful conversations that don’t focus on rationing healthcare or being a gatekeeper, but focuses instead on getting the right balance of harms and benefits,’ he said.
 
‘Importantly the guide talks about what can be done instead to help assess and reduce the risk of having a vascular event.’
 
Upcoming First do no harm topics include:

• ‘Excluding allergenic foods in maternal and infant diets’
• ‘Initiating opioids for chronic non-cancer pain’
• Associated topics for GPs – ‘Overdiagnosis’, ‘Over-testing’, ‘Managing uncertainty’

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