Folate (Vitamin B9) Test

About this test

This test measures your blood level of folate (vitamin B9), an essential B vitamin your body cannot make on its own and must obtain from food or supplements. Folate is required for producing DNA, forming red blood cells, supporting cell division, and — critically — preventing birth defects in early pregnancy.

Folate deficiency can develop within weeks to months, especially in people with poor diet, alcohol use disorder, certain GI conditions that affect absorption, or increased demand (such as pregnancy). Low folate causes a specific type of anemia (megaloblastic anemia) where red blood cells are abnormally large and don't function properly.

Components

• Folate (serum or RBC): Measures folate in the blood. Serum folate reflects recent dietary intake and can fluctuate with your most recent meals. Red blood cell (RBC) folate is a more stable measure of longer-term folate status. Your lab may report one or both depending on the test ordered. Results below the reference range indicate deficiency, which is easily corrected with supplementation under clinician guidance.

Who is this test for?

Folate testing is most relevant for women who are pregnant or planning to become pregnant — adequate folate is critical in early pregnancy to prevent neural tube defects, and the CDC recommends 400 mcg of folic acid daily for all women of reproductive age. It is also appropriate for anyone with signs of macrocytic anemia, people who drink alcohol heavily, and those taking medications that interfere with folate metabolism, such as methotrexate or certain anticonvulsants.