Non-HDL cholesterol is a non-comprehensive blood test that is not measured directly but rather derived from other lipid levels in the blood. It represents all cholesterol-containing lipoprotein molecules associated with atherosclerosis. It is calculated simply by subtracting the HDL (good) cholesterol value from the total cholesterol. Therefore, it includes LDL (bad) cholesterol, IDL (medium-density lipoprotein), and VLDL (very low-density lipoprotein), which carries triglycerides.