Folic Acid

A folic acid test measures the amount of folic acid in the blood. Folic acid is one of many B vitamins. The body needs folic acid to make red blood cells (RBC), white blood cells (WBC), platelets, new genetic material (DNA) in cells, and for normal growth. Folic acid also is important for the normal development of a baby (fetus).

Folic acid can be measured in the liquid portion of blood (plasma). This reflects a person's recent intake of folic acid in the diet. Folic acid is found in foods such as liver; citrus fruits; dark green, leafy vegetables (spinach); whole grains; cereals with added B vitamins; beans; milk; kidney; and yeast.

Folic acid may also be measured as the amount in the red blood cells. This test may be a better way than the plasma test to measure the amount of folic acid stored in the body. The amount of folic acid in red blood cells measures the level when the cell was made, as much as 2 months earlier. This level is not usually affected by the amount of folic acid in your diet each day. It is a more accurate way to measure the body's level of folic acid.

Women who are pregnant or planning to become pregnant need extra folic acid to make more red blood cells and maintain normal growth of their baby. Women who do not get enough folic acid before and during pregnancy are more likely to have a child born with a birth defect, such as a cleft lip or cleft palate or a neural tube defect, such as spina bifida.

Folic acid deficiency can result in a type of anemia called megaloblastic anemia. Mild folic acid deficiency usually does not cause any symptoms. Severe folic acid deficiency may cause a sore tongue, diarrhea, headaches, weakness, forgetfulness, and fatigue.

A folic acid test may be done to:

• Check for anemia. A folic acid test is often done at the same time as a test for vitamin B₁₂ levels because a lack of either vitamin may cause anemia.
• Check for malnutrition or difficulty absorbing (malabsorption) folic acid.
• See whether treatment for folic acid deficiency or vitamin B₁₂ deficiency is working.
• See whether a woman has enough folic acid to prevent certain birth defects and allow her baby to grow normally.

For the folic acid plasma test, do not eat or drink (other than water) for 8 to 10 hours before the test. If you take any medicines regularly, your doctor will talk to you about how to take these before the test.

You do not need to do anything before having a folic acid red blood cell test.

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then a bandage.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

There is very little chance of a problem from having blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

A folic acid test measures the amount of folic acid in the blood. Normal values vary from lab to lab.

High values

• High levels of folic acid in the blood may mean that you eat a diet rich in folic acid, take vitamins, or take folic acid pills. Consuming more folic acid than the body needs does not cause problems.
• High folic acid levels can also mean a vitamin B₁₂ deficiency. Body cells need vitamin B₁₂ to use folic acid. Therefore, if vitamin B₁₂ levels are very low, folic acid cannot be used by the cells, and high levels of it may build up in the blood. However, a folic acid test is not a reliable way to test for a vitamin B₁₂ deficiency.

Low values

• Low folic acid levels can mean you have a problem with your diet, alcohol dependence, or an eating disorder such as anorexia nervosa.
• Low folic acid levels can also mean you have a problem absorbing or using folic acid, such as a vitamin C deficiency, liver disease, celiac disease, sprue, or Crohn's disease.
• Low folic acid levels can cause problems for certain people. For example:
  • A pregnant woman needs extra folic acid for her growing baby.
  • People who have hemolytic anemia, a condition that causes the rapid destruction of red blood cells, need more folic acid to make more red blood cells.
  • People with certain conditions, such as kidney failure and some types of cancer, may use up folic acid quickly. They may need their blood to be cleaned using a machine (kidney dialysis).

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking some medicines, such as birth control pills, phenytoin (Dilantin), pyrimethamine (Daraprim), methotrexate, trimethoprim (Proloprim), pentamidine (Pentam 300), triamterene (Dyrenium), primidone (Mysoline), and phenobarbital.
• Using too much alcohol.
• Having conditions such as vitamin B₁₂ anemia or iron deficiency anemia.

• The American Heart Association recommends that you get the daily recommended intake of folic acid to prevent folic acid deficiency anemia. Many foods have folic acid, such as citrus fruits, leafy green vegetables, and vitamin-fortified cereals. Vitamin supplements also have folic acid.
• Taking folic acid before and during pregnancy can reduce the chance of having a baby with a neural tube defect or other birth defects, such as cleft lip or cleft palate. All women of childbearing age should take a daily supplement with 0.4 mg folic acid. Women who have a family history of neural tube defects, or who have had a baby with a neural tube defect, should take a daily supplement with 4 mg folic acid.
• The folic acid test is often done at the same time as a test for vitamin B₁₂. For more information, see the medical test Vitamin B₁₂.
• Research studies are being done to see whether folic acid supplements help reduce the chance of developing certain forms of cancer.
• Blood plasma levels of folic acid can be increased by eating foods rich in folate. If folic acid deficiency anemia is a concern, folic acid levels in the red blood cells can be measured.
• Homocysteine is an amino acid that is normally found in small amounts in the blood. However, an inherited disorder called hyperhomocysteinemia, which means that the levels of homocysteine in the blood are abnormally high, may promote atherosclerosis and coronary artery disease. Research has shown that folic acid lowers homocysteine levels. The American Heart Association recommends a healthy, balanced diet to provide the recommended daily amount of folic acid. Studies have shown that folic acid supplements may not lower the risk of heart disease or stroke.^{1, 2} For more information, see the medical test Homocysteine.
• For more information on folic acid deficiency anemia and what foods have folic acid, see the topic Folic Acid Deficiency Anemia.

Citations

1. Heart Outcomes Prevention Evaluation (HOPE) 2 Investigators (2006). Homocysteine lowering with folic acid and B vitamins in vascular disease. New England Journal of Medicine, 354(15): 1567–1577.

2. Bonaa KH, et al. (2006). Homocysteine lowering and cardiovascular events after acute myocardial infarction. New England Journal of Medicine, 354(15): 1578–1588.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.