High calcium could be a false positive

Dear Dr. Roach: I am an 80-year-old male who's very physically active. Six years ago, I had a coronary calcium scan resulting in a score of 3,708 with no symptoms. A few days later, a thallium treadmill stress test showed no problems.

I have aortic stenosis that recently reached the borderline-severe stage and is being dealt with. An angiogram a week ago showed no coronary artery blockage. What could account for the high CCS score? Could it be calcified plaque? — J.B.

People with very high calcium scores are very likely to have blockages in the arteries, and 3,708 is an exceptionally high calcium score. However, it's not an impossible result, and that is one of the problems with the calcium score from a CT scan of the heart. This is a false positive result, and is much more likely in older people. I would be concerned for other reasons for calcium deposition, such as high parathyroid hormone levels or kidney disease with high phosphate levels,.

It is possible to have a very low or even zero calcium score and have blockages in the arteries. Especially in younger people, plaque may not have calcium, so a person can have blockages without calcium.

The calcium score is a very good test to help stratify risk, but no test is perfect. I read several articles stating that there is no such thing as a false positive calcium score, but case reports in the literature confirm your result that it is possible. Adding dye to the calcium CT, a test called a CT angiogram, allows a look at the inside of the arteries as well. A CTA is nearly as good as a traditional angiogram, which is the gold standard for diagnosing coronary artery disease. However, dye adds additional risks and expense to the study, and it is often not covered by insurance. Your normal stress test provides additional reassurance.