Type of test Blood

Normal findings

 Serum: 5-25 ng/mL or 11-57 nmol/L (SI units)

RBC folate: 360-1400 nmol/L

Test explanation and related physiology

 Folic acid (folate), one of the B vitamins, is necessary for normal function of RBCs and white blood cells (WBCs). It is needed for the adequate synthesis of certain purines and pyrimidines, which are precursors for DNA. Blood folate levels require normal absorption by the intestinal tract. The finding of a low serum folate level means that the patient’s recent diet has been subnormal in folate content and/or that recent absorption of folate has been subnormal.

Tissue folate is best tested by determining the content of folate in RBCs. A low RBC folate can mean either that there is tissue folate depletion because of folate deficiency, which requires folate therapy, or that the patient has primary vitamin B12 (p. 969) deficiency, which blocks the ability of cells to take up folate. In the latter case, the proper therapy would be with vita min B12 rather than with folic acid.

Folic acid blood levels are performed to assess folate avail ability in pregnancy, to evaluate hemolytic disorders, and to detect anemia caused by folic acid deficiency (in which the RBCs are abnormally large, causing a megaloblastic anemia). These RBCs have a shortened life span and impaired oxygen carrying capacity. If folic acid blood levels are low, RBC folate is measured.

Folate deficiency is present in about 33% of pregnant women; many people with alcoholism; and patients with a variety of mal absorption syndromes, including celiac disease, sprue, Crohn disease, and jejunal/ileal bypass procedure. Folate binds to aluminum hydroxide. Patients with a chronic use of antacids or H2-receptor antagonists and with diets marginal in folate may experience low folate levels.

Elevated serum levels of folic acid may be seen in patients with pernicious anemia because vitamin B12 is needed to allow incorporation of folate into tissue cells. The folic acid tests are often done in conjunction with tests for vitamin B12 levels.

Interfering factors

• A falsely normal result may occur in a folate-deficient patient who has received a blood transfusion.

* Drugs that may cause decreased folic acid levels include alcohol, aminopterin, aminosalicylic acid, antimalHelveticas, chloramphenicol, erythromycin, estrogens, methotrexate, oral contraceptives, penicillin derivatives, phenobarbital, phenytoins, and tetracyclines.

 Procedure and patient care

• See inside front cover for Routine Blood Testing.

• Fasting: verify with laboratory

• Blood tube commonly used: red

• Some laboratories prefer an 8-hour fast. Instruct the patient not to consume alcoholic beverages before the test.

• Draw the specimen before starting folate therapy.

 Abnormal findings

 Increased levels

- Pernicious anemia

- Vegetarianism

- Recent blood transfusions

 Decreased levels

- Folic acid deficiency anemia

- Hemolytic anemia

- Malnutrition

- Malabsorption syndrome (e.g., sprue, celiac disease)

- Malignancy

- Pregnancy

-Alcoholism

- Anorexia nervosa