What type of apo-a should be measured?

[Frodo]

[ofonorow]

There is a confusion, in that little a and capital A refer to different proteins. I have never heard of "a1" and assume this refers to A1... Here is a list of all the "capital" lipoprotiens https://en.wikipedia.org/wiki/Apolipoprotein

I could be wrong about this, but here is the definition of Apo(A)

Apolipoprotein A
Apolipoprotein A makes up about 90% of the proteins in high density lipoprotein (HDL). So if you have a deficiency in apo A you will also have a deficiency in HDL. The levels of different types apolipoprotein A is important in controlling heart disease. Increased levels of apo A5 leads to increased triglyceride levels while apo A1 works with apo E to reduce triglyceride levels.

https://study.com/academy/lesson/apolipoproteins-function-structure-types.html

Notice apo(A) is associated with HDL, while Lp(a) is associated with LDL.

Notably neither wiki page, or the following web page mentions "little a" ...

Science direct on lipoprotiens https://www.sciencedirect.com/topics/neuroscience/apolipoproteins

I am speculating, but I would think the special designation Lp(a) was to separate it from apo(A) and the only reference I've see with apo(a) (without Lp(a)) was in the Pauling/Rath guinea pig experiments. I think apo(a) in humans always binds to an LDL (of varying size and density) and so in humans, the measurement you want is Lp(a).

[Frodo]

[Johnwen]