Apolipoprotein A and B

Apolipoprotein A1+ B Blood Test measures the amount Apolipoprotein A1 and B in the blood. This test helps to determine the risk for heart disease.

What is Apolipoprotein A 1 and Apolipoprotein B?

Apolipoprotein A or ApoA is a component of high-density lipoprotein (HDL, the good cholesterol). It removes the bad cholesterol within the blood vessels and from the body. Thus this protein helps to lower the risk of heart diseases.

High-density lipoprotein (HDL) is the smallest lipoproteins. It plays an important role in the removal of excess or unused cholesterol from the cells and returns this cholesterol to the liver. The liver breaks down the returned cholesterol to bile acids and salts. These bile acids and salts are eliminated through the intestine. If there is enough HDL present in the body, it prevents the build-up of fatty plaques or deposits in the blood vessels.

Apolipoprotein A is the major protein for the high-density lipoprotein and helps in its transport. It helps the HDL to take up cholesterol from the tissues and bound by receptors in the liver where the cholesterols to be destroyed. There are two types of Apolipoprotein A, Apo A-I, and Apo A-II. Apolipoprotein A1 is present in more proportion than Apolipoprotein A-II. Therefore low levels of Apolipoprotein A1 in the blood may increase the risk of cardiovascular diseases (heart diseases).

Apolipoprotein B or Apo B is the main protein component of low-density lipoprotein (LDL, the bad cholesterol) and very low-density lipoprotein (VLDL).

Chylomicrons are lipoproteins that carry dietary lipids to the liver. In the liver, these dietary lipids combine with Apo B to form triglyceride-rich VLDL. This combination is then transported across the bloodstream releasing lipids.

Lipoprotein lipase is an enzyme that helps to remove triglycerides from VLDL. As VLDL gets free off of triglycerides, it becomes intermediate-density lipoprotein (IDL) first and then LDL. The more cholesterol-rich LDL that are formed are transported across the body. Apolipoprotein B is the major protein for the low-density lipoprotein and helps in its transport. It helps the LDL to bind with receptors in the cells and promote the uptake of cholesterol into the cells. If there are high levels of LDL in the body, it results in the build-up of fatty plaques or deposits in the blood vessels. Therefore high levels of Apolipoprotein B in the blood may increase the risk of cardiovascular diseases (heart diseases).

Why this test is performed?

This test is performed to determine whether you have normal or abnormal levels of Apolipoprotein A1 and B in the blood. Your doctor may ask to perform this test if you have a family history of cardiovascular diseases or if you are at risk of developing cardiovascular diseases. This test is also recommended if you have an abnormal level of high-density lipoprotein (HDL) or low-density lipoprotein (LDL).

You may be advised to perform this test to diagnose the cause of abnormal lipid levels, especially when someone has elevated triglyceride levels. This test is recommended to monitor the effectiveness of treatment in individuals receiving treatment for high cholesterol.

How often this test is performed?

If you have a family history of cardiovascular diseases (heart diseases) your doctor may ask to perform this test in a 6 monthly or a yearly basis. If you are diagnosed with cardiovascular diseases (heart diseases), then you may have to perform this test on a regular basis as instructed by the doctor.

Precautions:

Certain medicines such as androgens, beta blockers, diuretics, progestins, estrogen, carbamazepine, estrogens, ethanol, lovastatin, niacin, oral contraceptives, phenobarbital, pravastatin, and simvastatin may affect the test results. Inform the healthcare provider about all the medications you take before the test.

If the test results show low levels of Apo- A1 and high levels of Apo- B than the normal range it may indicate an increased risk of cardiovascular disease.

Low levels of Apo- A1 are also seen in individuals with diabetes, coronary artery disease, chronic liver disease or chronic kidney disease.

High levels of Apo- A1 than the normal range may be seen in case of pregnancy. Individuals who do strenuous exercise and who take medicines such as carbamazepine, estrogens, ethanol, lovastatin, niacin, oral contraceptives, phenobarbital, pravastatin, and simvastatin may also show high levels of Apo-A1 in the blood.

High levels of Apo- B are also seen in individuals with diabetes, hypothyroidism or chronic kidney disease. Individuals with an inherited disorder called familial combined hyperlipidemia (high cholesterol and triglyceride levels) may also show increased Apo-B levels in the blood.

Low levels of Apo- B than the normal range are seen in individuals with hyperthyroidism, liver cirrhosis, malnutrition, severe illness, or Reye syndrome (a condition of swelling in the brain and liver damage). Individuals who had undergone surgery and who take medicines such as estrogen may also show low levels of Apo-B in the blood.

Individuals with a rare genetic condition Abetalipoproteinemia also called Apolipoprotein B deficiency may also show very low levels of Apo-B in the blood.

Based on the test results, your doctor may advise appropriate medical treatments, lifestyle modifications, or further diagnostic tests.