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), and platelets, 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 (serum). 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 can also be measured as the amount in the red blood cells. This test may be a better way than the serum 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 4 months earlier. This level is not usually affected by the amount of folic acid in your diet on a single day but indicates the typical amount in your diet over several months. 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.
Why It Is Done
A folic acid test may be done to:
- Check for the cause of 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 problems absorbing (malabsorption) folic acid.
- See if treatment for folic acid deficiency or vitamin B12 deficiency is working.
- See if a woman has enough folic acid to prevent certain birth defects and allow her baby to grow normally.
How To Prepare
For the folic acid serum 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.
How It Is Done
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 on the site and then put on a bandage.
How It Feels
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 a 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.
A folic acid test measures the amount of folic acid in the blood.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
7–30 nanomoles per liter (nmol/L) (SI units)
317–1422 nmol/L (SI units)
More than 160 ng/mL
More than 362 nmol/L
- 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. So if vitamin B12 levels are very low, folic acid can't be used by the cells, and high levels of it may build up in the blood. But a folic acid test is not a reliable way to test for a vitamin B12 deficiency.
- Low folic acid levels can mean you have a problem with your diet, alcohol use disorder, 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 fast destruction of red blood cells, need more folic acid to make more red blood cells.
- People who have 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).
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
- Eat a healthy, balanced diet to 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.
- You might need to take a folic acid supplement if you have anemia and can't get enough folic acid from food. Your doctor can tell you if you need to take a supplement.
- Taking folic acid before and during pregnancy can lower the chance of having a baby with a birth defect.
- The folic acid test is often done at the same time as a test for vitamin B12. To learn more, see the topic Vitamin B12.
To learn more about folic acid deficiency anemia and what foods have folic acid, see the topic Folic Acid Deficiency Anemia.
- Fischbach F, Dunning MB III (2015). A Manual of Laboratory and Diagnostic Tests, 9th ed. Philadelphia: Wolters Kluwer Health.
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Current as of: November 8, 2019
Author: Healthwise Staff
Medical Review: E. Gregory Thompson MD - Internal Medicine
Brian D. O'Brien MD - Internal Medicine
Adam Husney MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Joseph O'Donnell MD - Hematology, Oncology
Elizabeth T. Russo MD - Internal Medicine
Current as of: November 8, 2019