Low-density lipoprotein - Estimation of LDL particles via cholesterol content - in mmol/l
Low-density lipoprotein (LDL) is one of the five major groups of lipoproteins. These groups, from least dense to most dense, are: chylomicrons , very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), LDL, and High Density Lipoprotein (HDL), all of them, particles far smaller than human cells.
Lipoproteins transfer fats around the body in the water outside cells, can be sampled from blood and allow fats to be taken up by the cells of the body by receptor-mediated endocytosis.Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are typically composed of 80-100 proteins/particle (organized by a single ApoB for LDL and the larger particles) and transporting about 3,000 to 6,000 fat molecules/particle. The fats carried include cholesterol, phospholipids, and triglycerides; amounts of each vary considerably.
LDL particles pose a risk for cardiovascular disease when they invade the endothelium and become oxidized, since the oxidized forms are more easily retained by the proteoglycans. A complex set of biochemical reactions regulates the oxidation of LDL particles, chiefly stimulated by presence of necrotic cell debris and free radicals in the endothelium.
Increasing concentrations of LDL particles are strongly associated with increasing amounts of atherosclerosis within the walls of arteries over time, eventually resulting in sudden plaque ruptures and triggering clots within the artery opening, or a narrowing or closing of the opening, i.e. cardiovascular disease, stroke, and other vascular disease complications.
LDL particles (though far different from cholesterol per se) are sometimes referred to as bad cholesterol because they can transport their content of fat molecules into artery walls, attract macrophages, and thus drive atherosclerosis. In contrast, HDL particles (though far different from cholesterol per se) are often called good cholesterol or healthy cholesterol because they can remove fat molecules from macrophages in the wall of arteries.
A hereditary form of high LDL is familial hypercholesterolemia (FH). High LDL is termed hyperlipoproteinemia type II (after the dated Fredrickson classification).
Estimation of LDL particles via cholesterol content
Chemical measures of lipid concentration have long been the most-used clinical measurement, not because they have the best correlation with individual outcome, but because these lab methods are less expensive and more widely available.
The lipid profile does not measure LDL particles. It only estimates them using the Friedewald equation by subtracting the amount of cholesterol associated with other particles, such as HDL and VLDL, assuming a prolonged fasting state, etc.
There are limitations to this method, most notably that samples must be obtained after a 12 to 14 h fast and that LDL-C cannot be calculated if plasma triglyceride is >4.52 mmol/L (400 mg/dL). Even at triglyceride levels 2.5 to 4.5 mmol/L, this formula is considered inaccurate.Related formulas
|LDL||LDL cholesterol (mmol/l)|
|CTOTAL||total cholesterol (mmol/l)|
|HDL||HDL cholesterol (mmol/l)|
|k||factor : 0.20 if quantities in mg/dl and 0.45 if in mmol/l or 0.16 if both total cholesterol and triglyceride levels are elevated (in mg/dl) (dimensionless)|