Coronary calcium scoring is used to indirectly assess coronary atherosclerosis. Calcification occurs in atherosclerotic plaques and progresses with the severity of the process and is not seen in normal arteries. There is some correlation between the amount of calcification and the severity of coronary artery disease, though it is not a perfect one to one relationship. It is also uncertain whether calcification correlates with the chance of plaque rupture and consequent acute coronary syndromes. Though calcium can be related to the plaque burden, it may not be directly correlated with luminal stenosis as the plaque often grows abluminally, producing positive remodeling of the vessel wall.
It may seem that calcified plaques are likely to be stable and unlikely to rupture and predispose to acute coronary events. But those with higher calcium scores have a larger plaque burden, some of which may be calcified while others may not be. It is reasonable to assume that those with higher plaque can have some unstable plaques prone for rupture as well. This is how the coronary score gains importance as a risk predictor.
Calcium score between 100 and 400 project a relative risk ratio of 4.3 compared to those with no detectable coronary calcium (low risk group with calcium score = 0). In those with high calcium scores of 400 to 1000, the relative risk ratio is 7.2 and that for very high scores, greater than 1000, the relative risk ratio is 10.8. Calcium score is rather 100% specific for coronary plaques while it is not specific for obstructive coronary artery disease. But higher calcium scores increase the probability of having significant coronary stenosis.