Folate, Serum and Erythrocytes (RBCs)

Folate refers to all derivatives of folic acid. Folate is an essential vitamin present in a wide variety of foods such as dark leafy vegetables, citrus fruits, yeast, beans, eggs, and milk. Folate is vital to normal cell growth and DNA synthesis. A folate deficiency can lead to megaloblastic anemia and ultimately to severe neurologic problems. Folate levels in both serum and RBCs are used to assess folate status. The serum folate level is an indicator of recent folate intake. RBC folate is the best indicator of long-term folate stores. A low RBC folate value may indicate a prolonged folate deficiency. Other names: vitamin B9.

Normal range:

Serum folate: >6.5 ng/mL

RBC folate: 280 " “903 ng/mL

Use

Evaluation of folate deficiency

Interpretation

Increased In

Blind loop syndrome

Vegetarian diet

Distal and small bowel disease

PA

Decreased In

Untreated folate deficiency, associated with megaloblastic anemia

Infantile hyperthyroidism

Alcoholism

Malnutrition

Scurvy

Liver disease

Vitamin B12 deficiency

Dietary amino acid excess

Chronic hemodialysis

Celiac disease

Disorders of glutathione metabolism

Sideroblastic anemia

Pregnancy

Whipple disease

Amyloidosis

Limitations

Serum folate is a relatively nonspecific test. Low serum folate levels may be seen in the absence of deficiency, and normal levels may be seen in patients with macrocytic anemia, dementia, neuropsychiatric disorders, and pregnancy disorders.

Patients with low RBC folate or megaloblastic anemia should be evaluated for vitamin B12 deficiency. To distinguish between vitamin B12 and folate deficiency, determination of homocysteine (HCS) and methylmalonic acid (MMA) will help. In vitamin B12 deficiency, both HCS and MMA are elevated, whereas in folate deficiency, only HCS levels are elevated.