Apo B-100 levels are used, along with other lipid tests, to help determine an individual's risk of developing atherosclerotic heart disease and coronary artery disease (CAD). It is not used as a general population screen but may be ordered when a patient has a family history of heart disease and/or hyperlipidemia. It may be performed, along with other tests, to help diagnose the cause of hyperlipidemia, especially when someone has elevated triglyceride levels (preventing accurate LDL cholesterol calculations).

Sometimes doctors will order both Apo A-I (associated with high-density lipoprotein (HDL) - the "good" cholesterol) and Apo B-100 levels to get a ratio of A/B to obtain additional risk information.

Occasionally Apo B-100 levels may be ordered to monitor the effectiveness of lipid treatment. In rare cases, they may be measured to help diagnose a genetic problem that causes over- or under-production of Apo B-100.

Apo B-100 may be measured, along with other lipid tests, when your doctor is trying to evaluate your risk of developing atherosclerotic heart disease and when you have a personal or family history of heart disease and/or hyperlipidemia, especially when you have significantly elevated triglyceride levels. Sometimes Apo B-100 is monitored when you are undergoing treatment for hyperlipidemia.

Elevated levels of Apo B-100 correspond to elevated levels of LDL-C and are associated with an increased risk of CAD. Elevations may be due to a high fat diet and/or decreased clearing of LDL from the blood. Increased levels of Apo B-100 are seen with hyperlipidemia and in those patients with:

• Diabetes
• Drugs such as: androgens, beta blockers, diuretics, progestins (synthetic progesterones)
• Familial combined hyperlipidemia (an inherited disorder causing high blood levels of cholesterol and triglycerides)
• Hypothyroidism
• Nephrotic syndrome (a kidney disease)
• Pregnancy (levels increase temporarily and decrease again after delivery)

Apo B-100 levels may be decreased with any condition that affects lipoprotein production or affects its synthesis and packaging in the liver. Lower levels are seen with:

• Drugs such as: estrogen ( in post-menopausal women), lovastatin, simvastatin, niacin, and thyroxine
• Hyperthyroidism
• Malnutrition
• Reye syndrome
• Weight reduction
• Severe illness
• Surgery
• Abetalipoproteinemia (also called Apolipoprotein B deficiency or Bassen-Kornzweig Syndrome, a very rare genetic condition)
• Cirrohsis

A low ratio of Apo A-I to Apo B-100 (A/B) may indicate a higher risk of developing coronary artery disease.

Some elevations of Apo B-100 (and LDL-C) are due to mutations in the Apo B gene that cause it to produce Apo B-100 that is not recognized as easily by LDL receptors. This slows the clearing of LDL from the blood and increases the risk of heart disease.