A folate serum test is a common diagnostic blood test used to determine the concentration of folate, also known as Vitamin B9, circulating in the bloodstream. This measurement reflects the amount of the water-soluble vitamin currently available to the body’s cells. Analyzing the serum level helps health care providers assess a person’s recent dietary intake and overall nutritional status. The test provides a snapshot of the body’s short-term folate reserves, identifying potential deficiencies or excessive intake.
The Biological Role of Folate
Folate is an essential B vitamin required for numerous biological processes. Its primary function involves one-carbon metabolism, which is necessary for the creation of new genetic material. Specifically, folate is needed for the synthesis and repair of DNA and RNA in actively dividing cells.
This role in DNA synthesis makes folate important for tissues that undergo rapid turnover and growth. The formation of red blood cells (erythropoiesis) in the bone marrow depends on adequate folate supply. Insufficient folate prevents red blood cells from maturing properly, leading to abnormally large, dysfunctional cells that characterize megaloblastic anemia.
Folate refers to the naturally occurring forms of Vitamin B9 found in foods like leafy green vegetables, legumes, and citrus fruits. Folic acid is the synthetic form used in supplements and fortified foods such as cereals and breads. The body must convert synthetic folic acid into its active form, 5-methyltetrahydrofolate, before it can be used.
Since folate is water-soluble, the body does not store large reserves, requiring consistent dietary or supplemental intake. This characteristic means the serum test, which measures circulating folate, is sensitive to recent changes in diet.
When and How the Serum Test is Performed
A doctor typically orders a folate serum test when a patient presents with symptoms suggesting anemia, such as fatigue, weakness, or pallor. The test is a standard part of the diagnostic workup for megaloblastic anemia, a condition where red blood cells are larger than normal. It is also used to investigate malabsorption disorders, which prevent the small intestine from properly taking up nutrients.
The test monitors nutritional status in high-risk groups, including individuals with chronic alcohol use disorder or those taking medications that interfere with folate absorption. Pregnant women or those planning a pregnancy are routinely screened because low folate levels can significantly increase the risk of neural tube defects in the developing fetus.
The procedure involves a standard blood draw, or venipuncture, usually from a vein in the arm. The sample is sent to a laboratory, where the serum is separated and analyzed for its folate concentration. Patients are often instructed to fast for six to eight hours before collection, as folate concentration can temporarily increase after a meal.
Serum folate levels primarily reflect recent intake over the past few days. For a more complete picture of long-term folate stores, a physician may request a red blood cell (RBC) folate test. This test reflects the average folate level over the lifespan of the red blood cell, approximately three months. A Vitamin B12 test is frequently ordered simultaneously, as the two vitamins are metabolically linked.
What Folate Serum Levels Reveal
The results of a folate serum test are typically reported in nanograms per milliliter (ng/mL). The normal range generally falls between 2.7 and 17.0 ng/mL, though specific reference ranges vary by laboratory. A result within this range suggests sufficient circulating folate from recent dietary intake and absorption. Values outside this range indicate a potential nutritional problem requiring further investigation.
A low serum folate level, often defined as less than 2.0 ng/mL, points toward a deficiency. This deficiency impairs the body’s ability to create and repair DNA, manifesting as megaloblastic anemia. It may also cause symptoms like fatigue, irritability, or inflammation of the tongue. Common causes include inadequate dietary intake, malabsorption conditions such as celiac disease, and increased demand, such as during pregnancy.
A high serum folate level, typically above 17.5 ng/mL, is often a result of over-supplementation with folic acid. While excessive folate is generally not toxic, very high levels can mask a co-existing Vitamin B12 deficiency. This masking can lead to progressive and irreversible nerve damage if the B12 deficiency is left untreated. Managing a confirmed folate deficiency involves increasing dietary intake of folate-rich foods and starting folic acid supplementation. Monitoring the serum level after treatment confirms the patient is responding appropriately.