What the scan measures

The test is a quick CT of the heart, without needles or contrast dye. Calcium in the wall of a coronary artery is a footprint of atherosclerosis — the plaque process behind most heart attacks — and the scanner totals every speck of it into one figure, the Agatston score [1][2].

Reading the number

Broadly, the score falls into four bands [1][3]:

  • 0 — no detectable calcified plaque. A score of zero is a genuinely reassuring finding, predicting a low risk of coronary events over the following years [1][3].
  • 1–99 — mild plaque. Atherosclerosis is present but limited; attention turns to risk factors [1][3].
  • 100–399 — moderate plaque, and a risk that deserves active prevention [1][3].
  • 400 and above — extensive plaque: a strong signal to take prevention seriously with your doctor [1][3].

What the score is for

Its real home is the in-between. For people without symptoms whose estimated risk is borderline or intermediate, the score can settle the question a risk calculator leaves open — most often, whether preventive treatment such as a statin is genuinely worth starting [1][3]. In that situation it turns a statistical guess about people like you into a measurement of you.

What it doesn't tell you

Two limits matter. First, the score does not say whether any artery is narrowed or blocked: calcium marks the presence of plaque, not the degree of obstruction, and newer, softer plaque contains little calcium at all [1][2].

Second, it is not the test for symptoms. Chest pain is investigated differently — in the UK, guidelines make a CT coronary angiogram, a different scan that shows the arteries themselves, the usual first test [4][5]. And if you already have known coronary disease, the score adds nothing: the diagnosis is already made [1][3].

If you are considering one

A calcium score is most valuable when the result would actually change something — usually the decision to start, or comfortably not start, preventive treatment. That is a conversation to have with a doctor who can put the number in the context of your blood pressure, cholesterol, family history and everything else that makes up your real risk.