Apolipoprotein B
What it measures, and what changes the number.
Apolipoprotein B is the structural protein found on LDL, VLDL, IDL and lipoprotein(a) particles. Each of these particles carries one molecule of it, so the test effectively counts the number of these cholesterol carrying particles rather than the amount of cholesterol inside them.
It is usually read with LDL cholesterol and non-HDL cholesterol, because particle number and cholesterol content do not always move together, and with apolipoprotein A1 and lipoprotein(a) for a fuller lipoprotein picture. Some sites also show an LDL/ApoB ratio derived from it.
Apolipoprotein B is measured directly by immunoassay and is little affected by a recent meal, so a fasting sample is less critical than for triglycerides. It may appear on reports as ApoB or Apolipoproteína B.
Often read alongside: LDL cholesterol, Non-HDL cholesterol, Apolipoprotein A1, Lipoprotein(a), LDL/ApoB ratio