Dr Mike MacDonald

What is the LDL-C to ApoB Ratio?

LDL particles

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Do you want to know your Low Density Lipoprotein (LDL) particle size, but don’t want to spend thousands on a nuclear magnetic resonance test? (Doesn’t everybody…? 😊)The low density lipoprotein cholesterol to Apolipoprotein B (LDL-C/ApoB) ratio is a simple metric that can be used to approximate LDL particle size for less than $100. Let me explain…

Why is particle size important?

The theory is that smaller more dense LDL particles are more likely to cause atherosclerosis than larger “fluffy” particles. However, this is just a theory. It has been established that both large and small LDL particles have been found in atherosclerotic plaque so they both can cause atherosclerosis. Smaller particles probably are more atherogenic, BUT particle size is not the only determinant of atherosclerosis. For example total particle number in circulation and oxidized LDL particles also play a role alongside other risk factors.

How can LDL-C/ApoB ratio be a proxy for particle size?

There is one ApoB molecule on each LDL particle. Therefore, your ApoB number is directly correlated to the number of LDL particles you have in your blood.  The LDL-C is a measure of the average amount of LDL-cholesterol held in all your LDL particles in the blood sample.  Therefore, if you take the ratio of LDL-C / ApoB = Average total cholesterol in all ApoB particles / the number of ApoB particles it gives you a measure of the amount of cholesterol in each LDL particle. Which is an index of particle size!

How important is the LDL-C to ApoB Ratio?

Lets go back to basics. Biomarkers are things we can measure in the body that allow us to assess someone’s future risk (probability) of getting a disease.  LDL-P, LDL-C, ApoB, HDL, blood pressure are all biomarkers. Some of these markers are better risk predictors than others. For example, ApoB is a stronger predictor of atherosclerosis than LDL-C and HDL

Few studies have looked at how good the LDL-C:ApoB ratio is at measuring risk of atherosclerotic events like heart attacks and strokes. Some small studies have found the following:

OK, now here is the really important bit. This ratio has limited data to back it up, so far. There have been nowhere near as many studies looking at how this ratio predicts risk in comparison to LDL-C and ApoB.

How do you interpret your level?

The theory is that the lower your ratio, the smaller the particle size. A level of 1.2 has been quoted in 1 paper however this is of dubious quality. In my view this ratio is not particularly useful yet. Stick with ApoB and if you don’t have this then use LDL-C. These biomarkers are validated in multiple studies and are widely accepted.  LDL-C/ApoB ratio – Not ready for prime time YET…!

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