Here's my understanding: the LDL number is really just a calculation from the total cholesterol and HDL. LDL is made up of a number of different particles of which apo b and Lp(a) are ones often tested. Every molecule of apo b carries 1 molecule of cholesterol which can be deposited where it doesn't belong (arteries, etc), so for people with risk factors, such as my family history, getting the apo b number down was key. Lp(a) is hereditary (well, most of this is), and another risk factor.

Being on a statin got my LDL number to around 100, but with my family history and CAC score, it was determined it needed to be far lower. Added the Repatha injections to the mix and now my LDL is at 17 and my apo b in the normal range.