The apolipoprotein B (apo B) test is used, along with other lipid tests, to help determine an individual's risk of developing cardiovascular disease (CVD). It may be ordered if a person has a family history of heart disease and/or high cholesterol and triglycerides (hyperlipidemia). It may be performed, along with other tests, to help diagnose the cause of abnormal lipid levels, especially when someone has elevated triglyceride levels. Apo B is a protein that is involved in the metabolism of lipids and is the main protein constituent of lipoproteins such as very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL, the "bad cholesterol"). Elevated levels of apo B correspond to elevated levels of LDL-Cholesterol and are associated with an increased risk of cardiovascular disease (CVD).