Coronary Calcium Score: Basics and Beyond
Naveen L Pereira MD, Iftikhar J Kullo, MD
April 13, 2015
Naveen L Pereira MD: My name is Naveen L Pereira, Assistant professor of medicine and pharmacology at Mayo Clinic in Rochester, Minnesota. Today we will be discussing the very pertinent and interesting topic of coronary calcium testing, with professor of medicine Dr Iftikkhar Kullo, who has a strong research interest in preventive cardiology, with a focus on using biomarkers for identifying cardiovascular risk. Why is calcium associated with atherosclerosis?
Iftikhar J Kullo, MD: Calcification is part of the inflammation and repair processes that are ubiquitous in atherosclerotic lesions. Calcification occurs early in atherosclerosis, but we are not able to detect it with imaging until it increases in quantity, typically after the age of 40 in men and women. We can detect it with imaging in the later years, but it’s present in the very early stages of atherosclerosis.
Dr Pereira: Is CT scanning the most sensitive imaging technology to detect calcium?
Dr Kullo: At this moment, it is the standard test to detect coronary artery calcification. We have seen with histology confirmation that it accurately quantifies the amount of calcification. By quantifying calcium, we get an idea of the extent of atherosclerotic plaque burden, and although it is not a marker of plaque vulnerability, by showing the extent of disease, it gives an insight into the patient’s level of risk.
Interpreting the Calcium Score
Dr Pereira: If I order a calcium score, what will I see when I look at the report?
Dr Kullo: Two things must be considered. One is the absolute score, and the other is a percentile for that person’s age, sex, and ethnicity. What we consider abnormal is anything above the 75th percentile for age, sex, and ethnicity or an absolute score of 300 (Agatston units), as mentioned in the guidelines.Some people have an issue with that; they would say that any detectable or any calcification score >100 is abnormal.
The scoring is based on the intensity of the calcium signal and the location of the signal. In a sense, it gives the quantity of calcification present.
Dr Pereira: How strong are the data linking calcification identified by CT imaging and actual clinical outcomes?
Dr Kullo: The recent guidelines for risk assessment recommended four modalities for scenarios in which there is uncertainty about the patient’s level of risk: coronary calcium, family history, C-reactive protein, and ankle-brachial index. Of those four, the strongest data are for coronary calcification, and it’s clear that this is by far the best modality in terms of refining risk estimates when there is uncertainty about the patient’s level of risk or when the patient has an intermediate risk score. The data are fairly good; and; in fact, the question we ask is how often this reclassifies individuals when we are assigning risk based on risk calculators. It does this fairly often. In the MESA study, risk was reclassified on the basis of the calcium score 25% of the time; and even more often in the intermediate-risk group, in which nearly half were reclassified. The data are very good that as a marker of adverse outcomes, the calcium score goes above and beyond what we can get from the risk calculators.
Dr Pereira: Not only does it identify atherosclerosis, but it identifies the possibility of adverse cardiovascular events that could occur in that particular person.