LDL-C is usually calculated using the Friedewald equation. However, this measure can underestimate LDL-C level as triglycerides increase. Direct LDL-C measurements are also available and better reveal individual issues, but are less often promoted or done due to slightly higher costs.
LDL-C reflects the total content or concentration of cholesterol within LDL-C particles in mg/ml or mmol/L. Since the amount of cholesterol in each particle may vary, measuring LDL-C does not necessarily reflect the actual number of particles.
LDL-P (LDL particle number) measures the actual number of LDL particles (particle concentration, nmol/L). It appears that LDL-P may be a stronger predictor of cardiovascular events than LDL-C.
Low LDL-P is a much stronger predictor of low risk than low LDL-C. In fact, about 30 – 40% of those with low LDL-C may have elevated LDL-P. Therefore you can have low LDL-C but still be at risk for CVD, particularly if your LDL-P is elevated. Discordance is when LDL-C differs from LDL-P.
Lipoproteins play an essential role for the initiation and progression of atherosclerosis. Therefore it is very important for us to understand what regulates the production and clearance of atherogenic lipoprotein particles and how these mechanisms may be influenced.
LDL-C is only a measure of the cholesterol mass within LDL-particles. Thus, LDL-C only indirectly reflects the atherogenic potential of LDL particles. Apolipoprotein B (apoB) and LDL-P on the other hand reflect the number of atherogenic particles, with no mention of cholesterol mass. Therefore apoB and LDL-P are believed to be better risk predictors than LDL-C.
Reference Range for LDL-P
LDL-P is measured by a so-called NMR lipid profile test. A value of less than 1.000 is considered ideal. Above 2.000 is considered very high.
Apolipoprotein B (apoB)
Apolipoprotein B (ApoB) is an important component of many lipoproteins that are involved in atherosclerosis and cardiovascular disease.
Lipoproteins are the particles that transport cholesterol and triglycerides in the blood stream.
Lipoproteins are comprised of proteins (apolipoproteins), phospholipids, triglycerides and cholesterol. The lipoproteins vary in the major lipoprotein present, and the relative contents of the different lipid components. ApoB is an important component of many of the most atherogenic lipoprotein particles.
ApoB occurs in 2 main forms, apoB 48 and apoB 100. ApoB 48 is synthesized mainly by the small intestine. ApoB 100 is the apolipoprotein found in lipoproteins synthesized by the liver. Therefore, from the viewpoint of atherosclerosis and cardiovascular risk, apoB100 is the important one. ApoB 48 is primarily found in chylomicrons.
ApoB 100 is found in chylomicrons, VLDL, IDL, LDL and LP(a) particles. All these particles are atherogenic. Each of these particles contains a single apoB molecule. Therefore, measurements of apoB represent the total burden of the main lipoprotein particles involved in the atherosclerotic process.
Usually, 85-90 percent of apoB represent LDL particles. Thus, apoB reflects particle concentration, similar to LDL-P. Although measurements of apoB are not widely available, the assay has been standardized and does not require a fasting sample.
Apo B containing lipoproteins are the ones that are most likely to enter the wall of the arteries. They are capable of trafficking cholesterol into the artery wall, and if present in increased numbers they may be the main initiating factor in atherosclerosis. Retention of ApoB containing lipoprotein particles within the arterial wall is an essential part of the process.
The normal range for apoB is 40-125 mg/dL.
Usually less than 100 mg/dL is considered desirable in low or intermediate risk individuals.
Less than 80 mg/dL is desirable in high risk individuals, such as those with cardiovascular disease or diabetes.
