The calcium score is very accurate in detecting coronary calcium plaques. The CT scanner can take multiple images of the heart in thin sections, which allow the machine to calculate the calcium score based on the amount of calcification.
Do note that your calcium score only detects plaque that contains calcium, and in some people, they may have plaques which do not contain any calcium. These are fatty plaques made up of fat and cholesterol deposits which may not be detected with calcium score alone. Moreover, more calcium will be detected in the coronary arteries with increasing age, and this may lead to a higher calcium score detected in older persons.
Your cardiologist will determine which tests are most suitable for you, and utilise the information obtained from calcium score to give you an accurate risk assessment of coronary artery disease.