How is it used?
To help evaluate your risk of developing cardiovascular disease (CVD); and sometimes to help monitor treatment for high cholesterol or to help diagnose a rare inherited apo B-100 deficiency.
When to get tested?
When you have a personal or family history of heart disease and/or high cholesterol and triglyceride levels and your doctor is trying to determine your risk of developing CVD; sometimes on a regular basis when you are being treated for high LDL-cholesterol (LDL-C); rarely when your doctor suspects that you have an inherited apo B-100 deficiency.
How is it used?
Apo B-100 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"). Concentrations of apo B-100 tend to mirror those of LDL-C.
The apo B test is used, along with other lipid tests, to help determine an individual's risk of developing CVD.
This test may be a more reliable indicator of CVD than LDL-C and it may be performed, along with other tests, to help diagnose the cause of abnormal lipid levels, especially when a patient has elevated triglyceride levels.
In some situations, apo B-100 testing may be used in conjunction with LDL-C testing to determine if pharmacotherapy should be initiated.
Apo B levels may be ordered to monitor the effectiveness of lipid treatment as an alternative to LDL-C.
In rare cases, an apo B test may be ordered to help diagnose a genetic problem that causes over- or under-production of apo B-100.
When is it ordered?
Apo B-100 may be measured, along with other lipid tests, when a doctor is trying to evaluate a patient's risk of developing CVD and when a patient has a personal or family history of heart disease and/or abnormal lipid levels, especially when the patient has significantly elevated triglyceride levels.
Sometimes an apo B test is ordered to monitor a patient undergoing treatment for high LDL cholesterol.
What does the test result mean?
Elevated levels of apo B-100 correspond to elevated levels of LDL-C and to non-HDL-C and are associated with an increased risk of CVD. Elevations may be due to a high-fat diet and/or decreased clearing of LDL from the blood.
Some genetic disorders are the direct (primary) cause of abnormal levels of apo B-100. For example, familial combined hyperlipidemia is an inherited disorder causing high blood levels of cholesterol and triglycerides. Abetalipoproteinemia, also called Apolipoprotein B deficiency or Bassen-Kornzweig syndrome, is a very rare genetic condition that can cause abnormally low levels of apo B-100.
Abnormal levels of apo B-100 can also be caused by underlying conditions or other factors (secondary causes). For example, increased levels of apo B-100 are seen with:
- Use of drugs such as: androgens, beta blockers, diuretics, progestins (synthetic progesterones)
- 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 secondary causes such as:
- Use of drugs such as: estrogen (in postmenopausal women), lovastatin, simvastatin, niacin, and thyroxine
- Reye's syndrome
- Weight loss
- Severe illness
Is there anything else I should know?
Some elevations of apo B-100 (and LDL-C) are due to mutations in the apoB gene that cause it to produce apo B-100 that is not recognized as easily by LDL receptors. Others are in the LDL receptor system of the liver cell that recognizes apo B-100. These genetic defects impede the clearing of LDL from the blood and result in accumulations of LDL in the circulation, increasing the risk of heart disease.
Chylomicrons, the lipoprotein particles that carry dietary lipids to the liver, contain a lipoprotein called apolipoprotein B-48. It is about half the size of apo B-100 and is structurally related to apo B-100. It is not considered a risk factor for atherosclerosis and is not measured as part of the apo B test. The apo B test is specific for apo B-100.
Is there a charge for the test?
This test is not currently covered by provincial health insurance plans, but may be covered by your extended health insurance plan. Contact us to find out about the current fee for the test.
Note: Content on this page has been used and adapted with permission from Lab Tests Online.