Do you test LDL particle size?

Currently we do not.  We measure ApoB over LDL particle size because it is a better predictor of heart health risk, and it's also a more standardized measurement. ApoB can be measured through a serum test, whereas LDL particle size is measured primarily via NMR spectroscopy. The testing method for LDL-p is thus less comparable across labs, less standardized, and more expensive.

An LDL particle test gives the number of LDL particles and respective sizes of the particles in your bloodstream while your ApoB score is a measurement of the number of all potentially atherogenic particles.So the LDL-p is actually already captured within the ApoB measurement (in most people, ~90% of measured ApoB particles are LDL), but it's also capturing VLDL, IDL, chylomicron, and Lp(a) - all potentially atherogenic particles. And not that the size is not important, but when ApoB is measured alongside a standard lipid panel, all the metrics can be used to determine the larger story of your particle makeup.

A concordant result (high LDL and high ApoB) means there is a high number of potentially atherogenic particles, which refers to high risk. A discordant result (high LDL and optimal ApoB) actually corresponds to lower risk, since it means there is a lower number of potentially atherogenic particles - and they are likely larger and less dense (less atherogenic). You can also have discordance the other way: optimal LDL and high ApoB. This is demonstrating higher risk, since it means a greater number of smaller and dense particles, which we know is more atherogenic.

Even though we recognize the value of an LDL-p test, the evidence and context of an ApoB measurement is stronger and sufficient to get a solid picture of your heart health.