What's the difference between good and bad cholesterol?

LDL carries cholesterol into artery walls and drives plaque formation ("bad"). HDL is involved in reverse transport ("good"), though raising HDL with drugs hasn't reduced events. Non-HDL cholesterol and ApoB are better risk markers than HDL.

LDL and ApoB reflect the particles that deposit in artery walls, which is why LDL is the treatment target. Raising HDL with drugs has not reduced events in trials.

Non-HDL cholesterol — total minus HDL — is a useful single number, particularly if triglycerides are raised or the sample was not fasting.