Coronary artery calcium scoring for risk stratification

2018 ACC/AHA multisociety cholesterol guideline; NLA CAC statement

An unenhanced, gated, low-dose acquisition whose only job is to move a preventive treatment decision that is currently uncertain. Requested for a symptomatic patient it answers the wrong question; requested for someone already committed to treatment it answers no question at all.

An asymptomatic adult in whom the calculated cardiovascular risk sits close to a treatment threshold, and where the patient and clinician are undecided about starting preventive therapy.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

CT Coronary Calcium Score — Unenhanced ECG-Gated

CT Coronary Artery Calcium Score

What we'd amend, and why

Calcium in a coronary artery is already several hundred Hounsfield units denser than surrounding tissue, so iodine would only obscure it — the study is unenhanced by necessity, not by economy. ECG gating and contiguous fixed-thickness sections exist because the Agatston method is a threshold-and-area calculation defined on a specific acquisition; change the slice thickness or the kernel and the number changes, which is why serial scores from differently acquired studies are not comparable. The whole study lasts one breath-hold and delivers a small fraction of the dose of a contrast coronary angiogram.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Coronary Artery Calcium Score CT Coronary Calcium Score — Unenhanced ECG-Gated usually appropriate	Calcium in a coronary artery is already several hundred Hounsfield units denser than surrounding tissue, so iodine would only obscure it — the study is unenhanced by necessity, not by economy. ECG gating and contiguous fixed-thickness sections exist because the Agatston method is a threshold-and-area calculation defined on a specific acquisition; change the slice thickness or the kernel and the number changes, which is why serial scores from differently acquired studies are not comparable. The whole study lasts one breath-hold and delivers a small fraction of the dose of a contrast coronary angiogram.
Second line	CT Coronary Angiogram (CCTA) CT Coronary Angiogram — ECG-Synchronised	If symptoms appear, the question changes from population risk to whether this person has obstructive disease, and only a contrast angiogram answers that. It is also what a very high score in a borderline-symptomatic patient should prompt a conversation about, rather than a repeat score.

Pitfalls

Scoring a symptomatic patient. A zero score does not exclude obstructive disease in someone with typical angina, and using it as a gatekeeper is the commonest misuse of this study.
Requesting it for a patient already on treatment or already at high calculated risk — the result cannot change anything, and statin therapy itself increases plaque calcification.
Comparing serial scores acquired with different slice thickness or reconstruction, which changes the number independently of biology.
Reporting the absolute score without the age- and sex-specific percentile, which is what actually carries the risk message.
Reading a zero score as permanent reassurance rather than as a reason to defer and reassess.

Priors — what to pull first

Any previous gated or non-gated chest CT will already show whether coronary calcification is present, and often makes a dedicated score unnecessary for the qualitative question.
If a previous score exists, check the acquisition parameters before comparing. Repeat scoring at short intervals rarely changes management and is not a surveillance test.

What makes a good request

A good request states that the patient is asymptomatic, gives the calculated risk score, and says explicitly what decision is pending. If the answer would not change the decision, the scan should not happen.
The result is reported as an absolute Agatston score together with the percentile for age and sex, because the same absolute score means very different things in a 45-year-old and a 75-year-old.
A score of zero is powerful but not absolute: it does not exclude non-calcified plaque, and in young patients with diabetes, familial hypercholesterolaemia or severe hyperlipidaemia a substantial soft plaque burden can coexist with no calcium.

Scoring this once it is done

The classification and risk tools this question ends in.

Coronary Artery Calcium (Agatston) Score Categories MESA Coronary Calcium Percentile

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

CT Coronary Calcium Score — Unenhanced ECG-Gated CT Coronary Angiogram — ECG-Synchronised

Confirm locally

CT Coronary Calcium Score — Unenhanced ECG-Gated: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.