Folate

Overview

Folate measures the concentration of this essential B vitamin (vitamin B9) in blood, primarily as a cofactor in one-carbon metabolism for DNA synthesis, methylation reactions, and amino acid metabolism. Serum folate reflects recent dietary intake, while red blood cell folate indicates long-term tissue stores. Low levels indicate dietary deficiency, malabsorption, increased demand (pregnancy), or drug interference, while high levels may occur with recent supplementation. Folate testing is clinically useful for diagnosing megaloblastic anemia, preventing neural tube defects in pregnancy, and evaluating causes of hyperhomocysteinemia.

Clinical Use Cases

  • Diagnosing folate deficiency anemia (macrocytic anemia workup).
  • Evaluating malabsorption syndromes (celiac disease, inflammatory bowel disease).
  • Assessing nutritional status in pregnancy, alcoholism, or chronic hemolytic anemias.
  • Investigating unexplained hyperhomocysteinemia or neuropsychiatric symptoms.

Specimen Types

  • Serum (serum folate).
  • Whole blood (red blood cell folate).

Measurement Methods

  • Microbiological assay (Lactobacillus casei).
  • Competitive binding immunoassays.
  • High-performance liquid chromatography (HPLC).

Test Preparation and Influencing Factors

  • No fasting required, but avoid recent folate supplementation for accurate deficiency diagnosis.
  • Recent dietary intake dramatically affects serum folate (short half-life).
  • Alcohol, anticonvulsants (phenytoin), and methotrexate lower levels.
  • Hemolysis invalidates RBC folate; recent transfusion affects results.

Synonyms

  • Vitamin B9.
  • Folic acid (synthetic form).
  • Serum folate, RBC folate.

Further Reading

  • Folate Test; MedlinePlus;