CAC score

Coronary artery calcium (CAC) scoring uses a gated CT scan to measure calcium deposited in the walls of the coronary arteries, with burden quantified by the Agatston method. It is one of the most rigorously validated cardiovascular risk biomarkers available, yet it is frequently misread in both directions, dismissed because a score is "zero," or treated as a complete picture when it isn't.

What the score predicts

The MESA study established that CAC predicts coronary events independent of traditional risk factors across multiple ethnic groups, with risk rising steeply by burden: a CAC above 300 carries roughly ten times the event rate compared to zero [1]. That gradient is why clinicians use CAC to stratify, not screen. Adding CAC to standard risk-factor models meaningfully reclassifies intermediate-risk patients, with a net reclassification improvement of 0.25, the statistical foundation for CAC-guided statin decisions [2].

The "power of zero", and where it stops

A CAC of zero is good news. Studies show approximately 1% ten-year all-cause mortality in people who score zero [3], which is why the result is sometimes called the "power of zero." Cardiologist Peter Attia frames it plainly: a calcium score of zero means a lower risk of a coronary event at the population level, but it is not zero risk [4].

The same dataset makes the caveat concrete: within the CAC=0 group, smokers retained a hazard ratio of 3.97 and diabetics a hazard ratio of 3.36, meaningful residual risk that the zero score does not wash away [3]. The biological reason is that CAC images only calcified plaque, which has already hardened and stabilized. Soft, non-calcified plaque produces no calcium signal and is invisible to the test. Verhoeven's analysis suggests a CAC=0 result deserves contextual interpretation: zero amid active smoking, diabetes, or hypertension is suspect for underlying soft plaque; zero alongside excellent metabolic labs is reassuring [5].

Volume, density, and why two equal scores differ

CAC is a composite of plaque volume and plaque density. Volume correlates with risk as expected, more plaque, more events. Density moves in the opposite direction: harder, more calcified plaque is more stable and, for a given total score, carries paradoxically lower risk than softer calcified tissue. Verhoeven's analysis notes this means two patients with identical CAC scores can face meaningfully different cardiovascular trajectories [5].

This also explains a counterintuitive statin finding: statins can raise a CAC score over time by stabilizing soft plaque into calcified plaque, a net benefit that looks like worsening on a serial scan [5]. Patients who see their score rise while on statin therapy should not interpret that as treatment failure without clinical context.

Athletes and the limits of a single number

High-volume endurance athletes tend to carry more calcified plaque and higher CAC scores than sedentary controls, yet they do not show improved cardiovascular mortality. Verhoeven's analysis of the available data suggests CAC does not map straightforwardly to risk in this population without accounting for fitness context [6, 7]. (The exercise-plaque relationship is itself contested, more on that below.)

When to go further

Contrast CT angiography (CCTA) with low-attenuation-plaque quantification detects the non-calcified plaque that CAC misses and better characterizes what may be reversible. Verhoeven's analysis identifies it as the preferred tool where accessible when soft-plaque burden is the clinical question [5].

Reading the key bands

A score of zero signals low, not absent, risk. Scores of 1-99 indicate mild burden; 100 and above represents significant calcified plaque. Age- and sex-based percentile context matters alongside the raw number: a CAC of 80 in a 45-year-old carries different implications than the same score in a 70-year-old.

Where the evidence is contested

The athlete-plaque paradox generates genuine disagreement. Verhoeven's analysis suggests that improved CAC in endurance athletes reflects stable, calcified plaque. This plaque does not translate into higher mortality risk [6, 7]. The Master@Heart study challenges this framing. It raises concern that lifelong high-volume training may increase non-calcified plaque burden, the kind CAC does not capture. Neither position is settled. Serious endurance athletes with improved CAC scores should understand two things. First, the standard risk tables built on population data may not apply cleanly to them. Second, CCTA may offer a more complete picture than CAC alone [5].

References

1. Detrano 2008 MESA, NEJM — CAC predicts coronary events across ethnicities · PubMed 18367736
2. Polonsky 2010 MESA, JAMA — CAC reclassification NRI 0.25 · PubMed 20424251
3. Blaha 2009, JACC Img — CAC=0 ~1% 10-yr mortality (but smokers/diabetics retain risk) · PubMed 19520338
4. raw/attia/attia07-lpa-deep-dive.txt
5. raw/physionic/physionic-at-home-test-find-plaque.txt
6. raw/physionic/physionic-exercise-duration-plaque*.txt
7. Physionic — Exercise-plaque paradox (athlete plaque type)