Is a Zero Calcium Score Reassuring Enough? Understanding the Warranty Period

Coronary artery calcium (CAC) scoring has quietly become one of the most valuable tools we have in preventive cardiology. It’s quick, non-invasive, relatively inexpensive, and remarkably informative.

For those unfamiliar with the test itself, I’ve written an overview explaining what CAC scoring is and how it works— you can read it here.

When someone’s CAC score comes back as zero, it often brings a sense of relief — and for good reason. In most cases, it tells us that the short-term risk of a heart attack or cardiovascular death is very low.

But what does that really mean in clinical practice?
How long can that reassurance be trusted?
And when — despite a score of zero — should we still be cautious?

When and Why Do We Use Coronary Calcium Scoring?

Coronary artery calcium scoring is most often used in asymptomatic individuals at borderline or intermediate risk of cardiovascular disease, where traditional risk calculators leave room for uncertainty. It’s particularly helpful for refining treatment decisions — such as whether to start statins, aspirin, or other preventive strategies — when guideline recommendations are unclear.

Unlike CT coronary angiography (CTA), which requires contrast and images of the coronary lumen to detect stenosis and soft plaque, CAC scanning uses a low-dose (low-radiation), non-contrast CT scan to detect and quantify calcified plaque — minimizing radiation exposure while providing a clear view of calcification.

CAC scanning  doesn’t reveal obstructive lesions or non-calcified (soft) plaque, but it’s simpler, faster, and exposes patients to minimal radiation. I’ve explored the differences between CAC and CT angiography in more detail in this article.

What Does a Coronary Calcium Score Reflect?

A CAC scan detects the presence of calcified plaque in the coronary arteries — the vessels that supply blood to the heart. The results are reported as an Agatston score, which quantifies both the area and density of calcium deposits.

While a score of zero indicates no visible calcium, it doesn’t mean the arteries are entirely free of atherosclerosis. Non-calcified plaque — especially in younger individuals or those with metabolic dysfunction — can still be present but undetected by CAC scanning.

From a biological standpoint, calcification is a late-stage response to vascular injury and inflammation. As atherosclerotic plaques age and remodel, they can undergo calcification as part of a “healing” process. Smooth muscle cells and macrophages promote calcium deposition, which can stabilize plaques — but also act as a durable marker of cumulative plaque burden. The presence of calcium, therefore, reflects established disease, whereas its absence suggests little or no mature plaque formation.

Why Is a Score of Zero So Reassuring?

Despite its limitations, a CAC score of zero remains one of the strongest negative risk markers in cardiovascular prevention. It offers unique value because it visualizes actual disease — or in this case, the lack of it — rather than relying on population-based risk prediction.

Several key studies have reinforced this:

• MESA (Multi-Ethnic Study of Atherosclerosis): Among individuals with CAC=0, the annual cardiovascular event rate was just 0.13% — substantially lower than predicted by traditional risk scores. [1]
• BioImage Study: Showed that CAC scoring could reclassify many intermediate-risk individuals as low risk, reducing overtreatment and improving risk discrimination. [2]
• SCOT-HEART Trial: Found that patients with no coronary calcium had a very low incidence of myocardial infarction, even in the presence of symptoms. Calcium presence correlated strongly with underlying coronary disease. [3]

These findings support the concept of a “warranty period” — a term describing the timeframe during which a CAC=0 result predicts low short-term risk. [4]

What Is the Warranty Period?

The concept of a “warranty period” was first popularized through longitudinal follow-up in studies like MESA and later supported by BioImage and SCOT-HEART. It refers to a window — typically 5 to 10 years — during which the absence of coronary calcium is associated with a very low risk of cardiovascular events, even in the presence of traditional risk factors like high LDL-C or hypertension.

• In MESA, many participants with CAC=0 remained event-free for up to 10 years. [5]
• However, the protective effect can shorten in older individuals, those with diabetes, or those with worsening metabolic profiles.
• Repeat scanning is sometimes considered after 5–7 years, especially if risk factors change or new symptoms emerge.

It’s important to recognize that the warranty period is not infinite. A zero today doesn’t guarantee a zero tomorrow — but it gives strong, near-term reassurance that significant disease is unlikely.

Do you Still Need a Statin?

Often, the answer is no — at least not right away.

Recent guidelines from both the European Society of Cardiology (ESC) and the American College of Cardiology (ACC/AHA) support the use of CAC scoring to individualize statin decisions in primary prevention. A CAC score of zero can provide a strong rationale to defer statin therapy, particularly in patients at intermediate risk who are hesitant to start lifelong medication [6]

Here’s why:

• CAC modifies absolute risk. It can shift someone from an estimated 10-year ASCVD risk of 7% down to less than 1% — a level where the net benefit of statins becomes far less certain.
• No calcium, no atherosclerosis? If calcified plaque is absent, it’s unlikely that there is significant established disease to treat. For many patients, this changes the conversation from “Should we treat your cholesterol?” to “Is there any evidence of disease that needs treatment?” However, there is an important caveat: CAC scoring detects only calcified plaque. Non-calcified, or “soft,” plaques — which may still be clinically relevant and potentially vulnerable — can be missed. These are more common in younger individuals or those with high metabolic risk and can only be visualized with contrast-enhanced CT coronary angiography (CTA), not a calcium scan.
• Empowers shared decision-making. A zero score provides a clear, visual argument that allows patients and clinicians to make more confident, personalized choices.

This approach helps avoid unnecessary treatment and potential side effects, while maintaining vigilance through lifestyle modification and regular follow-up.

A Tool for Precision Prevention?

A CAC score of zero is not a free pass. It doesn’t eliminate the need for healthy lifestyle habits, blood pressure control, or long-term risk monitoring. But it is an exceptionally powerful tool for distinguishing those who would benefit from aggressive intervention from those who can take a more conservative path.

Used in the right context, CAC=0 allows us to practice precision prevention — treating the right patients, at the right time, for the right reasons.

This article was written with the assistance of ChatGPT, an AI language model developed by OpenAI, to help refine and structure the content.