How Common Are Inaccurate Coronary Artery Calcium Scans?

One reason the  skeptical cardiologist has been so enthusiastic about coronary calcium (CAC) scans is that I have found them to be highly reproducible and highly accurate.

Unlike most  imaging tests in cardiology if we perform a CAC on the same individual in the CT scanner of hospital A and then repeat it within a few days in the CT scanner of hospital B we expect the scores to be nearly identical.

Also, unlike most other imaging tests we don’t expect false negatives or false positives. If the CAC score is zero there is no coronary calcification-high sensitivity. If the score is nonzero there is definitively calcium and therefore atherosclerotic plaque in the coronaries-high specificity.

This is  because calcium as defined in the Agatson score is literally black and white-a pixel is either above or below the cut-off. Computer software automatically identifies on the scan. A reasonably trained CT tech should be able to identify the calcium that is residing in the coronary arteries based on his or her knowledge of the coronary anatomy as registered on CT slices. Using software the total Agatson score is calculated.

A physician reader (either cardiologist or radiologist) (who should have a very good understanding of the cardiac and coronary anatomy ) should review the CT techs work and verify accuracy.

A recent case report, however, has demonstrated that the above  assumptions are not always true.

Franz Messerli, a pre-eminent researcher in hypertension and a cardiologist describes in fascinating detail a false-positive CAC scan he underwent in 2013.  He was told he had a score of 804 putting him in a high risk category consistent with extensive plaque formation.

After consulting with cardiologist friends and colleagues he decided to put himself on a statin and aspirin despite having an excellent lipid profile.

Messerli assumed that the CAC score was not a false positive (although later in his article he indicates he had questioned the reading) writing:

“although one can always quibble with ST segments or wall motion abnormalities, on the CAC the evidence is rock-hard, you actually with your own eyes can see the white calcium specks! ‘Individuals with very high Agatston scores (over 1000) have a 20% chance of suffering a myocardial infarction or cardiac death within a year’—although I did not quite classify, this patient information coming from esteemed Harvard cardiology colleagues3 was hardly reassuring.

(His reference 3 for the 20% risk of MI or cardiac death in a year for CAC score >1000 is suspect. It is a 2003 “patient page” on coronary calcium in Circulation which does not have a reference for that statistic.)

A more recent study found patients with extensive CAC (CAC≥1000) represent a unique, very high-risk phenotype with CVD mortality outcomes (0.80%/yr) commensurate with high-risk secondary prevention patients (0.77%/yr) from the FOURIER trial)

Six years after the diagnosis Messerli was at a Picasso exhibition, “leisurely ambling between his Blue and Pink Period “when he developed chest pain.

To further evaluate the chest pain he underwent a coronary CT angiogram and this demonstrated pristine and normal coronary arteries, totally devoid of calcium.

He did have a lot of mitral annular calcification (MAC). The CCTA images below show how close the MAC is to the left circumflex coronary artery (LCX).



















The slice above shows how the MAC would appear on the CT scan designed to assess coronary calcium.  It’s position is very close to that of the circumflex but an experienced reader/tech  should have known this was not coronary calcification.

MAC is a very common finding on echocardiograms, especially in the elderly and it is likely that this error is not an isolated one.

Dr. Messerli writes

After relating these findings to the cardiologist who did the initial CAC, he indicated that most likely someone mistook mitral annular calcification as left circumflex calcium. This was hardly reassuring, since I specifically had asked that obvious question after receiving the initial CAC

Around the time I read Messerli’s case report I encountered a similar, albeit not as drastic case. A CAC scan showed a significant area of calcification near the left circumflex coronary artery which was scored as circumflex coronary calcification.


The  pattern of this calcification is not consistent with the known path of the circumflex coronary in this case. When it was eliminated from the scoring the patient had a zero score. The difference between a nonzero score and a zero score is hugely significant but for patients with scores >100 such errors are less critical.

I have also encountered cases where extracardiac calcium mimics right coronary calcification.

There are some important take-home points from my and Dr. Messerli’s experience.

  1. False positive CAC scans do occur. We don’t know the frequency. If the scans are not overread by a competent cardiologist or radiologist with extensive experience in cardiac CT these mistakes will be more common

When I asked Dr. Messerli about this problem he responded

I am afraid you are correct in that CAC scores are generated by techs and radiologists and cardiologist simply sign the report without verifying the data. Little doubt that MAC is most often missed.
     2. Like other cardiac imaging tests (such as echocardiography) having an expert/experienced/meticulous  tech and reader matters.
    3. Dr. Messerli and I agree that a research project should be done to ascertain how often this happens and to evaluate the process of reading and reporting CAC.
4. Patients should look at the breakdown of the calcium in the CAC by coronary artery. Whereas it is not uncommon to see most of the calcium in the LAD it is rare to see a huge discrepancy in which the circumflex coronary artery score is very high and the LAD score zero. Such a finding should warrant a review of the scan to see if MAC was included in error.
Skeptically Yours
N.B. Dr. Messerli’s report can be read for free and makes for entertaining reading.
I was very intrigued by two comments he made at the end:
  1. “Had my CHD been diagnosed a decade earlier, guidelines might well have condemned me to taking beta-blockers for the reminder of my days.6 This, as Philip Roth taught us in ‘The Counterlife’, might have had rather unpleasant repercussions.7

Until recently I had never read anything by Philip Roth but when he died last year I read his Pulitzer Prize winning  1987 novel American Pastoral and liked it. Given this Roth reference involving beta-blockers I felt compelled to get my hands on “The Counterlife.” The book is a good read (much better IMHO than American Pastoral) and one of the main plot points relates to the side effects (see my post on feeling logy) a character suffers from a beta-blocker. Stimulated by a desire to be able to perform sexually if taken of the medication, the character undergoes coronary bypass surgery and dies.

2. “As stated by Mandrola and true in the present case, ‘given the (lucrative) downstream testing that often occurs when coronary calcium is found in asymptomatic people, the biggest winners from CAC screening may be the testers rather than the tested’.”

I feel the CAC in the right hands should not lead to (lucrative or inappropriate) downstream testing in the asymptomatic (see my discussion on this topic here.)



16 thoughts on “How Common Are Inaccurate Coronary Artery Calcium Scans?”

  1. I didn’t see a breakdown of the coronary artery agatston scores but above 800 would most likely indicate widespread calcification beyond the LCX, do you feel that would be a correct assumption? Beyond that 2 questions.

    First since soft plaque or non ossified lesions are not reflected in CAC scans, do you feel that is a shortcoming of this test? From my basic understanding, soft plaque is much more vulnerable to becoming a thrombo/embolitic event as opposed to calcified plaque.

    My other question is plaque regression. Could the patient made lifestyle changes that drastically reduced environment for plaque development and perhaps regression? I do feel this scenario is unlikely due to the high initial agatston score but I have read many anecdotal stories about regression of plaque, but not a lot of scientific substantiation of patients accomplishing this in a quantifiable fashion in a controlled study.

    1. Christian,
      Yes. The vast majority of the time with a score over 800 all three coronary arteries will have some calcium.
      The CAC inability to detect soft plaqur or vulnerable plaque is a shortcoming. Such visualization of early noncalcified plaque requires coronary CT angiography. This is why I will repeat nonzero scans in high risk younger individuals
      This was not a case of regression. The MAC was present on the first and second scans. His true initial CAC score was zero.

  2. I had a CT Scan in June, 2018. My Agatston score was 659 and I was told there was a high likehood of significant narrowing of at least one coronary artery. So I was sent for another scan in August and this was their findings:

    On August 9, 2018 you underwent a CT scan with findings of mild atherosclerotic eccentric calcified plaque at the origin of the left main coronary artery. Moderate focal atherosclerotic plaque in the proximal circumflex artery approximately 1.3 cm from the origin. The stenosis was approximately 70-80%. Moderate eccentric calcified plaque approximately 1.4 cm from the origin of the left anterior descending coronary artery causes 80-90% stenosis. 70% focal stenosis right coronary artery approximately 3 cm from the origin causes 70-80% stenosis. Approximately 6 cm from the origin of the right coronary artery was a focal eccentric calcified plaque causing 70-80% stenosis.

    I was scheduled for an angiogram and my cardiologist told me to expect possible bypass surgery because of the extensive blockage instead of stents.

    The angiogram found normal, smooth arteries with only mild (less than 30%) blockage in one artery. All of the others were normal and clear. I would say that something was definitely misread in my CT scan.

    I have a meeting with the Director of Radiology on Friday. What is an appropriate question for her? Obviously, something was seriously misread.

    1. Reading a coronary CT angiogram requires extensive training and expertise. Extensive calcification makes the readings much more difficult and can lead to over calling the degree of stenosis. This degree of overcall raises questions about the qualifications and training of the reader which would be worthwhile to ask about.

  3. Thank you. I have a meeting tomorrow with the Director of Radiology at the hospital that performed the test. If I get copies of the original film, are you available for a second opinion? Since I’m in California, are you able to do this via e-mail or the web in some manner?

  4. What is the frequency or possibility of a false negative CAC? My husband, 58 yrs had a scan in June 2017 and received a score of 2. Eighteen months later he had a heart attack. It was in his right distal artery where there was a 95% blockage. They also discovered an 80% blockage in the LAD. He had 3 stents placed. He was about 20 lbs overweight at the time, never smoked, with an LDL of 78 and overall cholesterol of 130. It was a shock and none of the docs seem to have an explanation. They all just shrug their shoulders. Any thoughts?

    1. Your question is a good one but needs to be clarified. A CAC is designed to measure calcium in the coronary arteries. A false negative CAC would be one that called a zero score in a patient who had a high score. This is very unusual in my experience.
      But what happened to your husband represents a limitation of the CAC in completely predicting who will or won’t have a heart attack in the near future.
      The CAC score improves our ability to see who is at high risk but is definitely not perfect.The CAC does not see early soft plaque which precedes the development of calcium in the arterial wall. this soft plaque tends to be more vulnerable to rupture and thus causing myocardial infarction.
      thus a low score for age (your husband’s was 36th percentile for 58 year old white males) puts a patient in a lower risk category but doesn’t exclude the possibility of soft fatty plaque build up which can cause heart attacks.
      This is a situation where I would look carefully for other risk factors such as Lp(a) or chronic inflammation (high CRP).

  5. Can this inaccuracy extend to incidental findings on a CAC scan? I recently had a scan with a 0 score, however there was an incidental finding of “Calcified lesions are noted within left pulmonary parenchyma possibly calcified granulomas versus lymph nodes”. My cardiologist hasn’t followed up with me about this finding.

    1. Michael,
      No. Those are highly likely to be benign findings in the lungs unrelated to coronary calcification at all. In the midwest the majority of us have been exposed to histoplasmosis spores and this is a common X-ray finding related to histo.

  6. Dr AnthonyP,

    I am a 54 year old male with high blood pressure and normal cholesterol. I have had two CT scans with contrast is in the past 3 years. One about 2.5 years ago and one a little over a month ago. Both showed the same results. Calcium score of 0 but a 50-70% stenosis of soft plaque in the mid LAD. After the first scan, my dr put my on statins and we will continue to monitor it. Is the fact that nothing has changed in 2.5 years a good thing or should I be worried? Thanks.

    1. That’s interesting. I think it unusual that you had such a significant soft plaque 3 years ago and no calcium has been deposiited in it over 3 years. So it makes me wonder about the reality of the soft plaque.
      I would have expected the plaque to regress a little and to change its characteristics from completely soft (and presumably vulnerable) to hardened and calcified (and presumably less vulnerable).

  7. I have read the book “beat the heart attack gene” which talks about The Bale Doneen Method. Don’t know if you are familiar with this, but they talk about inflammation in the body, insulin resistance and other causes of heart attacks that with simple test can be detected and prevented. There is clinic in Florida, I was thinking about making an appointment for an evaluation, but it is very expensive. Any thoughts?

    1. I hadn’t heard of ‘bale doneen”. Researching their publication it seems very similar to my approach, especially the utilization of CIMT and CAC to guide treatment which I’ve written extensively about in the sections on subclinical atherosclerosis on this site. they also utilize statins and other standard cholesterol drugs. So, it seems unlikely it would be worth paying huge anounts of money for it. I did send an email to the main author on their study asking about what diet they utilize but he hasn’t responded yet.

  8. Dr. P,

    How do you assess risk based on a calcium score for a patient that is a long-term statin user?

    If statins increase calcification as part of the “healing” process then don’t statin users have higher baseline scores than non-statin users?

    Many thanks (and Happy Thanksgiving!)

    1. LMB
      This is a great question without a clear-cut answer. If the score is zero it is helpful. If it is above average for age it likely confirms the utility of the statin in that patient. If super high for age you might consider higher dosing and look for Lipoprotein (a) or do advanced lipid particle testing.

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