Modified LDL, Low Density Lipoprotein
Atherosclerotic plaque with lipid laden macrophages (scavenger cells) can only be produced if modified LDL is generated in the arterial wall. Macrophages will not take up unmodified LDL. More than 95% of LDL in the blood is unmodified LDL. Some modified LDL leaks out of the vascular wall and can be measured but techniques for doing so have not been standardized for routine clinical use. Measurement of total LDL in the blood is obviously very deceptive and almost unrelated to what is happening in the vascular wall.
How modified LDL is generated is still a mystery but has something to do with diet.