High LDL cholesterol is causally linked to a greater risk of cardiovascular disease. ApoB measures the number of harmful particles and can provide a sharper picture, especially with high triglycerides. What constitutes a healthy value depends on the overall risk profile, including blood pressure, smoking, and diabetes.
LDL cholesterol tells you how much cholesterol is carried in the harmful particles in your blood, and that number is directly linked to your risk of cardiovascular disease: the higher it is, the greater the risk, and that relationship is causal, not merely a statistical pattern. You can measure it with a standard blood test at your GP, which is usually covered by insurance. What a 'good' value looks like for you depends on your overall picture, because blood pressure, smoking and diabetes carry equal weight.
ApoB is a complementary measurement that does not count the amount of cholesterol but the number of harmful particles themselves. That distinction can matter: two people with the same LDL can have a different number of particles, and it is those particles that end up in the vessel wall. When triglycerides are high, LDL can even underestimate your true risk, whereas ApoB provides a sharper picture in that situation. It is also a standard blood draw, increasingly included as part of a routine lipid panel, and you can simply request it from your GP.
Together, LDL and ApoB therefore provide a more complete picture than either one alone, particularly if your triglycerides are on the high side or your LDL sits right on a borderline value. What you do with that information, whether lifestyle changes or possibly medication, is something to discuss with a doctor based on your overall risk profile.
Overview covering multiple factors (2 research records, 2 sources). The strength of evidence differs by component, read the answer for the nuance.