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Screening BODY HANDBOOK
Screening · §109
Coronary Artery Calcium (CAC) Score
A heart-disease risk calculator built from your age, blood pressure, and cholesterol can only guess what's in your arteries; a coronary artery calcium scan looks at them directly. Ten seconds in a CT machine, no contrast, no needle, and you walk out with one number — the Agatston score — that quantifies hardened plaque you've already built up. Zero means a fifteen-year window of very low cardiac event risk; a number in the high hundreds means you have the same disease as someone who's already survived a heart attack, you just don't know it yet.
Test · Once Evidence Moderate Chapter Screening

If you're between 40 and 75 and your doctor has ever said "we could try a statin" without sounding fully convinced, this is the test that answers the question. About a hundred dollars at most outpatient imaging centers, one appointment, no preparation. The result either takes the statin question off the table for a decade or hands you a concrete reason to get serious. The catch worth naming up front: a zero score is reassuring but not magic — in adults under forty-five and in some high-Lp(a) patients, plaque can be there without having calcified yet.

Coronary calcium isn't the disease; it's the scar tissue the disease leaves behind. Heart-attack plaque starts as cholesterol-laden particles burrowing into the artery wall — soft, lipid-rich, biologically active. Over years, the body lays down calcium inside mature plaques the way a healing wound lays down scar. The Agatston score counts those calcified deposits inside the heart's own arteries and adds them up. Any score above zero means atherosclerosis is there — not "might develop" but is — and the bigger the number, the more accumulated disease.

That's why the score works as a risk number where bloodwork alone can mislead. Your cholesterol panel describes the inputs that drive plaque formation. The calcium score describes how much plaque those inputs have actually produced in your particular arteries over your particular life. Two people with the same LDL can have a calcium score of 0 and 600, and they are not the same patient.

How well it actually predicts trouble

Adding a calcium score to a standard risk calculator changes the answer for about a third of people who run it. Half of those move into a lower risk category, half into a higher one — meaning a third of intermediate-risk adults are currently being told the wrong thing about their heart-attack odds.

At the low end, a score of zero is the strongest reassurance the test offers. In a follow-up of 9,715 asymptomatic adults with zero calcium, annual mortality stayed under 1% for fifteen years — a real "warranty period" of low risk, confirmed in the broader MESA data and shorter (around 5–10 years) in diabetics and adults over 75 Valenti et al. 2015 Mortensen et al. 2022. At the high end, a score above 1,000 places you in the same event-rate bracket as someone with an already-documented heart attack — roughly five times the cardiovascular event rate of someone with zero, and people in that bracket benefit from being treated like secondary-prevention patients from day one Peng et al. 2020.

The reason this evidence base isn't graded as airtight: nobody has run the trial where you randomise half the population to a calcium scan plus guideline-driven treatment and the other half to standard care without imaging, then count deaths a decade later. Cardiology guideline bodies — the American Heart Association, the American College of Cardiology, the National Lipid Association — treat the prediction-improvement evidence as enough and endorse selective use Grundy et al. 2019 Orringer et al. 2021. The US Preventive Services Task Force wants the missing trial first and currently rates the evidence insufficient USPSTF 2018. Both positions are defensible; the cardiology side is where most clinicians actually practice.

What "intermediate risk" actually hides

If a primary-care visit ever ended with "your numbers are okay-ish, we could try a statin, up to you" — that's the bucket this test was built for. The Pooled Cohort risk calculator your doctor used spits out a 10-year heart-attack probability between about 5% and 20% for a huge chunk of adults over fifty, and the recommendation at that level is genuinely ambiguous. Without a calcium score, you and your doctor are flipping a coin you can't see. It's an especially hard call for women, whose cardiovascular risk standard calculators capture least well — and a calcium number puts a figure on what their arteries are actually doing.

What that ambiguity costs, when nobody breaks it: among intermediate-risk adults in the MESA cohort, roughly a third had zero calcium and would have been started on a statin they didn't need; another fifteen-to-twenty percent had a score above 100 and were on the runway for a heart event nobody was treating like it Nasir et al. 2015. Those second-bucket people are the ones who show up in emergency rooms in their late fifties having "the heart attack out of nowhere" — except it wasn't out of nowhere, it was building for fifteen years and there was a $100 test that would have found it.

The forecast for someone in that hidden-high-burden bucket, untreated: the chest pain you blame on indigestion at 58, the stress test that suddenly shows something at 62, the stent at 65, the conversation with your kids about whether you can still travel. Heart disease is still the leading cause of death; primary prevention exists, and most of it lives in a decision the calcium score was specifically designed to help you make.

Getting one — when, where, what to expect

The mainstream window is 40–75 with at least one cardiovascular risk factor (high LDL, high blood pressure, family history of early heart disease, smoking history, diabetes), and uncertainty about whether to start a statin. Earlier — 35 or 40 — is reasonable if a parent or sibling had a heart attack before 55, or if your Lp(a) is elevated. Later than 75 is rarely indicated; most people that age are already on treatment or not, and the score won't change much.

How to read what comes back: 0 means no detectable hardened plaque — strong reassurance, no statin needed in most cases. 1–99 means mild plaque present; statin therapy is increasingly favoured as you cross 55. 100–299 is moderate plaque; statin therapy is clearly indicated. 300–999 is extensive plaque; high-intensity statin and likely low-dose aspirin. 1,000 or above is treated like established heart disease — high-intensity statin to drive LDL below 55 mg/dL, aspirin, aggressive blood pressure control Orringer et al. 2021.

What most people get wrong about the number

The single biggest misread: people assume the calcium in their arteries is the dangerous thing, and that the goal is to lower the score. Backwards. Calcified plaque is the more stable phenotype — the body's attempt to wall off and stabilise lesions that started out soft and inflamed. The number measures how much disease you've accumulated, not how active it currently is.

Which is why the second confusion catches everyone off guard: starting a statin will not lower your calcium score on a repeat scan. It will, on average, raise it slightly, even as it cuts your heart-attack risk in half. The drug stabilises soft plaque by converting it toward the calcified phenotype — exactly the change that makes you safer but the number larger. Repeat scans cannot be used to judge whether your statin is working Orringer et al. 2021.

The third one: a zero score does not mean "no heart disease, ever, full stop." It means your odds of a heart event over the next decade-plus are very low, with the warranty shortening if you're diabetic or already over 75 Mortensen et al. 2022. It does not erase the rest of your risk profile — high blood pressure, smoking, and diet still matter, and a zero today does not lock in a zero a decade from now if your inputs change.

Where the test quietly underperforms

The honest weak spot: the scan measures hardened plaque, and not all plaque has hardened yet. In adults under about 45, atherosclerosis is usually still in its early, lipid-rich, soft-plaque phase — biologically active, rupture-prone, and invisible to a calcium-only scan. A 38-year-old with high LDL, high Lp(a), and a strong family history of early heart attacks can have real, growing plaque and still score zero. For that profile, the calcium scan is not the right first test — coronary CT angiography, which uses contrast and shows both soft and calcified plaque, carries more signal, as do bloodwork markers like ApoB and Lp(a).

The same blindspot shows up in two other groups. Diabetics tend to develop a faster-progressing form of disease where the soft-plaque phase is more dangerous and the warranty period of a zero score is shorter — five to ten years rather than fifteen Mortensen et al. 2022. People with significantly elevated Lp(a) can have the same pattern, particularly when they're under fifty. None of this invalidates the test for its target audience — middle-aged adults with conventional risk factors — but it explains why "I got a zero, I'm fine" is too clean an answer for someone in their thirties or forties with an aggressive family history.

The other failure mode is operational rather than biological. People sometimes get scanned, see the absolute number, panic at the percentile, and start chasing the score itself. The number is information for a treatment decision — start a statin, add aspirin, get serious about blood pressure — not a target to optimise. A patient whose calcium climbs from 200 to 300 on a statin is doing exactly what the treatment is supposed to do, and a clinician familiar with the data won't be alarmed.

Cost, insurance, finding a center

In the US, expect to pay out of pocket. Most private insurers and Medicare don't cover the scan as preventive screening — they point to the USPSTF's "insufficient evidence" rating and decline to pay. A handful of state mandates (Texas notably) require coverage in certain age brackets, some self-insured employers cover it, and HSA and FSA funds qualify under IRS rules. Self-pay pricing at standalone imaging centers usually lands at $99–$150; hospital-based radiology departments can run higher. Call ahead and quote the CPT code 75571 if a receptionist sounds unsure what test you're asking for.

Outside the US, availability is uneven. In most of Europe, the scan is straightforward to obtain as part of a broader cardiac evaluation but rarely covered as standalone preventive screening; in Australia and Canada it's increasingly available cash-pay at private centers. Anywhere with a multidetector CT scanner and a cardiologist or radiologist who reads coronary calcium can produce a valid Agatston score — the test isn't proprietary and doesn't require specialised equipment beyond what most modern hospitals already have.

The downstream cost matters too. Acting on a high score usually means a generic statin (under $50 a year), maybe low-dose aspirin (under $20 a year), maybe more frequent cardiology follow-up. Acting on a zero score means continuing whatever you were doing, possibly with the statin question put away for a decade. Neither path is expensive in steady state; the scan is the front-loaded part.

What changes after you get the number

The week after a zero score, the change is mostly internal — the low background hum of "should I be doing something about my heart" goes quiet. Most people don't realise how much mental space it was taking until it's gone. The next physical, the next time a cousin has a cardiac event, the next time a friend posts about their statin: you have an actual answer instead of a vague unease, and the answer holds for years Valenti et al. 2015 Mortensen et al. 2022.

The week after a positive score, the change is concrete and a bit harder. There's a real first conversation with a clinician about a statin, sometimes about aspirin and blood pressure too. Most people feel a little shaken for a few days — finding out you have measurable atherosclerosis in your fifties is news, even when it's the kind of news that comes with a plan. Then the plan settles in: a $4-a-month pill at breakfast, lipid panel every six months for the first year, blood pressure cuff at home. The day-to-day cost is small. What you traded for it is the version of the future where, at 62, the chest pain in the parking lot isn't indigestion.

Over a decade, that's where the longevity argument lives. Statin therapy in primary prevention cuts heart-attack risk by roughly a third and total mortality measurably across a decade of treatment, with most of the benefit concentrated in the patients who actually had subclinical disease to begin with — which is precisely the group the calcium score identifies Nasir et al. 2015. The test doesn't extend your life. It tells you which side of the statin question you're actually on, so the treatment that does extend your life finds the right person.

Related tests and what's next

The calcium scan sits inside a small constellation of cardiovascular tests worth knowing about. ApoB is a blood test that counts the actual cholesterol-carrying particles driving plaque formation — a better single number than the LDL on a standard lipid panel and often a better target for treatment. Lp(a) is a once-in-life blood test for an inherited risk factor that conventional cholesterol panels miss entirely; high Lp(a) is one of the conditions where a calcium scan in your forties can quietly underperform. Coronary CT angiography (CCTA) uses IV contrast to image both calcified and soft plaque — the right next test when the calcium scan is zero but the rest of the picture suggests real risk, or when you have chest pain that needs evaluating. Blood pressure, taken seriously at home, is the cheapest and most consequential cardiovascular measurement most people skip.

Related in the handbook
Alternatives
  • — A risk calculator only guesses what's in your arteries; the scan looks directly — use it when the estimate is borderline.
Related
  • — The calcium scan looks at the artery directly; the advanced panel measures the drivers — they're complementary.
  • — A zero calcium score can still miss plaque in high-Lp(a) people — pair the scan with the lipid markers.
  • — Early kidney disease accelerates coronary calcification and is itself a major heart risk; the scan helps gauge it.
  • — For a woman with hard-to-read risk, a CAC score puts a number on what her arteries are actually doing.
  • — Calcium in the heart arteries means atherosclerosis everywhere. An older man who ever smoked should also ask about the one-time aortic scan.
  • — Chronic hostility is an independent heart-disease risk; if it's your pattern, this scan quantifies the plaque it adds to.
  • — If you have unexplained erectile trouble, a CAC scan checks the artery disease that's often underneath it.
  • — For someone with familial high cholesterol, a CAC scan helps gauge the artery damage already underway.
  • — If your score is high, lowering LDL hard matters — and these are the drugs that go beyond a statin.
  • — A man whose morning erections quietly disappeared has a reason to get this scan; the penile arteries fail before the coronary ones.
  • — The arterial calcium this scan finds is what K2 is meant to help prevent depositing in the first place.
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