Per my comment in the thread that ru442 linked, I do believe that coronary calcium shows past history. The issue is "soft plaque" which the test doesn't see. However, where there is a lot of calcium, there is usually soft plaque too. The idea is if you can hold volume increases to <15%/year your risk is relatively small and nearly that of someone with no calcium. Increases in density are not a problem as the calcium is just "hardening" existing plaque. The Agatston score (which is what is commonly quoted) is a combination of volume and density. My understanding of score calculation is that a analyst (radiologist) looks at a slice. If they see calcium, they measure the area and score the "brightness" (density) 1, 2, 3 or 4. To compute an Agatston score, the density value of the slice is multiplied by the area and then by the slice width, which is either 2.5 or 3 mm, depending on the machine. This is then summed for all slices and there you have the Agatston score. So measuring after 3 years, you'd like to know what the average annual volume (sum of area times slice width) increases is. If less than 15%, you are in good shape. The Agatston score can increase just by increasing the density, and that is OK as hard plaque is not the issue. It is just that increases in volume are usually associated with soft plaque.
Tincup I nominate you to write a Wiki page on CCSs 'at your leisure' . It could include this incredibly helpful text above, the different machine types, and link to this article plus MD comments weighing the pros and cons. The page could be linked to from the phrase in [url=Interpreting LDL Particle Number (LDL-P) and other lipid subparticles through advanced lipid tests]this section[/url] on the Cholesterol etc page