Folate (Folic Acid), Serum
FOLIC ACID. Folic acid is a water-soluble B-vitamin first identified in 1930 by Wills and Mehta as "Wills factor." Wills factor cured the anemias of pregnant women in India, a clinical condition that commonly results from undernutrition. This vitamin was later isolated from spinach leaves and named folic acid (Latin folium, leaf). Unlike most bacteria and yeast, mammals cannot synthesize folate and, therefore, require folate in the diet. This vitamin is present in the body as a family of at least nine structurally related chemical compounds that are collectively referred to as folate. The term folic acid refers to a synthetic form of the vitamin. Folic acid, which is biologically inactive, is found in foods that have been fortified with it. Folic acid is also the form that is present in nutritional supplements. Folic acid can be converted by living cells to a biologically active form called tetrahydrofolate. This active form serves the same biological function as natural folates. The terms "folic acid" and "folate" are therefore often used interchangeably.
Chemical Forms of Folate
The different forms of folate found in the body exist primarily as modified forms of tetrahydrofolate. Each tetrahydrofolate form differs by modification of the selected positions in the molecule that involve the placement of a single carbon unit. Additionally, folate derivatives found in cells contain a glutamate polypeptide tail that consists of two to eight glutamate residues in length. This polyglutamate chain is required for folates to perform their biochemical functions and also to retain folate in the cell. The glutamate chain prevents the molecule from crossing cell membranes.
Vegetables are good dietary sources of naturally occurring folate, especially dark green leafy vegetables. Citrus fruits and fresh juices, berries, legumes, liver, and whole grains are other good sources. Most naturally occurring folates are sensitive to degradation by air and heat but are stabilized when bound to proteins present in foods. For this reason, fresh fruits and vegetables are the best sources of dietary folates since many food folates are destroyed during food preparation. Dietary folates contain a polyglutamate chain that must be removed by digestive enzymes in the intestine. These enzymes leave a single glutamate residue on the folate, and the folate is then absorbed by the intestinal cell. Most folates are taken up by the liver, which is the primary storage site for folate. Folates can then be redistributed to other tissues from the liver. Glutamate chains are re-elongated by the body after the absorption of folates with single glutamates.
Overview of Folate Metabolism
Folate serves as a cofactor that delivers single carbon units to particular enzymes that catalyze biochemical reactions. These folate-dependent biochemical reactions are referred to collectively as one-carbon metabolism. Folate functions in both the cytoplasm and mitochondria, the energy-producing units, of mammalian cells. Folate metabolism in mitochondria is responsible for the generation of formate, a source of one-carbon unit. Formate escapes the mitochondria and is a primary source of the single carbon units for one-carbon metabolism in the cytoplasm. One-carbon metabolism in the cytoplasm is required for the synthesis of DNA precursors, and the amino acid methionine from its precursor, homocysteine. Methionine, in turn, is converted to the cofactor S-adenosylmethionine or SAM. SAM serves as an additional source of single carbon units in the form of methyl groups that are required for other metabolic reactions including the methylation of DNA, RNA, and proteins. SAM also is required for the synthesis of phospholipids, neurotransmitters, and many small metabolites.
Folate as a Therapeutic Target
Folate-dependent reactions are fundamental for DNA synthesis and maintenance of DNA integrity. Therefore, folate is required for cell growth and replication. It is not surprising that folate-dependent enzymes have proven to be effective targets for antitumor and antimicrobial drug therapies. These pharmaceutical agents are structurally similar to folate and are referred to as antifolates. Agents including 5-fluorouracil and methotrexate (and related antifolates) bind to folate-dependent enzymes by mimicking the structure of folate but do not serve the same biological function. These agents enter the cell and inhibit folate-dependent reactions associated with DNA synthesis and result in cell death. Antifolates are used in the treatment of many cancers, Crohn's disease, rheumatoid arthritis, lupus, and other autoimmune disorders.
Folate Deficiency and Disease
The most common impairments of folate metabolism result from inadequate folate intake, certain drug therapies, smoking, malabsorption disorders, alcoholism, genetic mutations, and subtle individual genetic variations that occur normally in populations. Additionally, certain dietary factors can interfere with folate absorption in the gut and result in malabsorption of the vitamin. Inadequate folate status has been reported in many population groups including pregnant and lactating women, women twenty to forty-four years of age, adolescents, and the elderly. Folate requirements are greatly increased during pregnancy due to the high demand for folate by the growing fetus and placenta. Folate deficiency can present itself clinically as megaloblastic anemia, a clinical condition associated with enlarged red blood cells due to decreased DNA synthesis. Other clinical symptoms include an inflamed, redlooking tongue, nausea, vomiting, diarrhea, anorexia, hyperpigmentation, and fever. Folate deficiency during pregnancy is highly associated with several congenital defects including spina bifida. Population studies implicate impaired folate metabolism in other pathologies including cardiovascular disease, colon cancer, cervical dysplasia, and pre-eclampsia.
Folate and Homocysteine
One of the first biochemical indicators associated with impaired folate metabolism is increased serum homocysteine (resulting from decreased methionine synthesis). Both folate and vitamin B12 are required for converting homocysteine to methionine. Plasma homocysteine level is a sensitive marker of folate status, but homocysteine can be influenced by other vitamins, including vitamin B6 and B12 status, as well as age. The relationship between folic acid and homocysteine levels in the body is important because of the association between homocysteine and vascular disease. Elevated plasma homocysteine is now considered an independent risk factor for atherosclerotic vascular disease. The risk of cardiovascular disease rises in proportion to an individual's serum homocysteine concentrations. Some studies also suggest an independent role of folate deficiency in cardiovascular disease. The relationship between homocysteine and disease is not understood, but two mechanisms are the focus of current research. Homocysteine contains a reactive thiol group that can modify proteins and affect their function. Alternatively, homocysteine can also be converted to S-adenosylhomocysteine, which is a potent inhibitor of many methylation reactions that modify DNA proteins and influences gene expression. Either or both of these mechanisms may account for pathologies that are associated with elevated homocysteine in humans.
In 1998, the National Academy of Sciences released the Dietary Reference Intake (DRI) values for folate that include a recommended dietary allowance (RDA) of 400 micrograms for males and females aged fourteen years and younger. For these individuals, the source of folate is not important. However, it is recommended that women of childbearing age consume an additional 400 micrograms of folic acid per day from fortified foods and/or supplements in addition to the intake of food folate from a varied diet. It is critical that women be folate-sufficient prior to pregnancy, since most birth defects that result from folate deficiency occur before the twenty-ninth day of pregnancy, often before the woman realizes she is pregnant. Maintaining adequate folate status is especially critical for women with a history of bearing children with neural tube defects, to prevent future incidence of birth defects. Pregnant women should consume an additional 600 micrograms of synthetic folate per day in addition to a naturally folate-rich diet. It is not normally recommended that anyone consume more than 1 milligram of folate per day.
The RDA is expressed as dietary folate equivalents (DFEs) because synthetic folic acid is more easily absorbed in the intestine than naturally occurring folate. One microgram of naturally occurring food folate is equivalent to 0.6 microgram of folic acid from fortified foods or supplements consumed with meals and to 0.5 microgram of supplements not consumed with meals. Because of recent federal regulations for food fortification, synthetic folic acid can now be found not only in dietary supplements, but also in enriched grain products (0.43 to 1.4 micrograms of folic acid per pound grain product) such as flour and pasta. Initial results from the fortification program indicate that plasma folate levels have more than doubled among adults who do not use folic acid supplements. The effect of this program on reducing spina bifida and other folate-associated birth defects and pathologies is yet to be determined.
Folic Acid Deficiency
The prevalence of folic acid deficiency has decreased since the United States and Canada introduced a mandatory folic acid food fortification program in November 1998. People with excessive alcohol intake and malnutrition are still at high risk of folic acid deficiency.
The significance of folic acid deficiency is compounded further by the following attributes:
- An association of folate deficiency with elevated homocysteine, leading to increased arteriosclerosis risks
- The reduced incidence of neural tube defects with folate supplementation
- The role of folate in the occurrence of cancer
Hence, folic acid clearly is of consequence in public health in the United States, especially because heart disease and cancer constitute the number 1 and number 2 causes of mortality in the United States. This article explores the mechanisms and manifestations behind folate deficiency, as well as its ramifications with regard to health and disease at large.
Folic acid is composed of a pterin ring connected to p-aminobenzoic acid (PABA) and conjugated with one or more glutamate residues. It is distributed widely in green leafy vegetables, citrus fruits, and animal products. Humans do not generate folate endogenously because they cannot synthesize PABA, nor can they conjugate the first glutamate.
Folates are present in natural foods and tissues as polyglutamates because these forms serve to keep the folates within cells. In plasma and urine, they are found as monoglutamates because this is the only form that can be transported across membranes. Enzymes in the lumen of the small intestine convert the polyglutamate form to the monoglutamate form of the folate, which is absorbed in the proximal jejunum via both active and passive transport.
Within the plasma, folate is present, mostly in the 5-methyltetrahydrofolate (5-methyl THFA) form, and is loosely associated with plasma albumin in circulation. The 5-methyl THFA enters the cell via a diverse range of folate transporters with differing affinities and mechanisms (ie, adenosine triphosphate [ATP]–dependent H+ cotransporter or anion exchanger). Once inside, 5-methyl THFA may be demethylated to THFA, the active form participating in folate-dependent enzymatic reactions. Cobalamin (B-12) is required in this conversion, and in its absence, folate is "trapped" as 5-methyl THFA.
From then on, folate no longer is able to participate in its metabolic pathways, and megaloblastic anemia results. Large doses of supplemental folate can bypass the folate trap, and megaloblastic anemia will not occur. However, the neurologic/psychiatric abnormalities associated with B-12 deficiency ensue progressively.
The biologically active form of folic acid is tetrahydrofolic acid (THFA), which is derived by the 2-step reduction of folate involving dihydrofolate reductase. THFA plays a key role in the transfer of 1-carbon units (such as methyl, methylene, and formyl groups) to the essential substrates involved in the synthesis of DNA, RNA, and proteins. More specifically, THFA is involved with the enzymatic reactions necessary to synthesis of purine, thymidine, and amino acid. Manifestations of folate deficiency thereafter, not surprisingly, would involve impairment of cell division, accumulation of possibly toxic metabolites such as homocysteine, and impairment of methylation reactions involved in the regulation of gene expression, thus increasing neoplastic risks.
A healthy individual has about 500-20,000 mcg of folate in body stores. Humans need to absorb approximately 50-100 mcg of folate per day in order to replenish the daily degradation and loss through urine and bile. Otherwise, signs and symptoms of deficiency can manifest after 4 months.
The current standard of practice is that serum folate levels less than 3 ng/mL and a red blood cell (RBC) folate level less than 140 ng/mL puts an individual at high risk of folate deficiency. The RBC folate level generally indicates folate stored in the body, whereas the serum folate level tends to reflect acute changes in folate intake.
Data from the National Health and Nutrition Examination Survey (NHANES) 1999-2000 indicate the prevalence of low serum folate concentrations (< 6.8 nmol/L) decreased from 16% before folic acid fortification to 0.5% after folic acid fortification. In elderly persons, the prevalence of high serum folate concentrations (>45.3 nmol/L) increased from 7% before fortification to 38% after fortification. The latest results from NHANES are available.
Countries that do not have a mandatory folic acid food fortification program have higher rates of folic acid deficiency. For example, a population based study in Iran (where there is no fortification) showed an age-adjusted prevalence of hyperhomocysteinemia (Hcy ³15 micromol/L) of 73.1% in men and 41.07% in women (aged 25-64 y).
Casey et al examined the effects over 1 year of a free weekly iron-folic acid supplementation and deworming program in 52,000 Vietnamese women of childbearing age. The investigators collected demographic data and blood and stool samples at baseline and at 3 and 12 months following the implementation of the program.
Findings included a mean Hb increase of 9.6 g/L (P < 0.001) and a reduction in the presence of anemia from 37.5% of the women at baseline to 19.3% at 12 months. Iron deficiency was also reduced, from 22.8% at baseline to 9.3% by 12 months, as well as hookworm infection (76.2% at baseline to 23.0%) in the same period.
A discussion of selected national Australian policies is presented in Lawrence et al.
Folate deficiency can cause anemia. The presentation typically consists of macrocytosis and hypersegmented polymorphonuclear leucocytes (PMNs). More detailed laboratory findings are discussed in the Workup section.
The anemia usually progresses over several months, and the patient typically does not express symptoms as such until the hematocrit level reaches less than 20%. At that point, symptoms such as weakness, fatigue, difficulty concentrating, irritability, headache, palpitations, and shortness of breath can occur. Furthermore, heart failure can develop in light of high-output cardiac compensation for the decreased tissue oxygenation. Angina pectoris may occur in predisposed individuals due to increased cardiac work demand. Tachycardia, postural hypotension, and lactic acidosis are other common findings. Less commonly, neutropenia and thrombocytopenia also will occur, although it usually will not be as severe as the anemia. In rare cases, the absolute neutrophil count can drop below 1000/mL and the platelet count below 50,000/mL.
Elevated serum homocysteine and atherosclerosis
Folate in the 5-methyl THFA form is a cosubstrate required by methionine synthase when it converts homocysteine to methionine. As a result, in the scenario of folate deficiency, homocysteine accumulates. Several recent clinical studies have indicated that mild-to-moderate hyperhomocystinemia is highly associated with atherosclerotic vascular disease such as coronary artery disease (CAD) and stroke. In this case, mild hyperhomocystinemia is defined as total plasma concentration of 15-25 mmol/L and moderate hyperhomocystinemia is defined as 26-50 mmol/L.
Genest et al found that a group of 170 men with premature coronary artery disease had a significantly higher average level of homocysteine (13.7 ± 6.4). In another study, Coull et al found that among 99 patients with stroke or transient ischemic attacks (TIAs), about one third had elevated homocysteine.
Elevated homocysteine levels might act as an atherogenic factor by converting a stable plaque into an unstable, potentially occlusive, lesion. Wang et al found that in patients with acute coronary syndromes, levels of homocysteine and monocyte chemoattractant protein-1 (MCP-1) were significantly higher.MCP-1 is a chemokine characterized by the ability to induce migration and activation of monocytes and therefore may contribute to the pathogenesis of CAD. Homocysteine is believed to have atherogenic and prothrombotic properties via multiple mechanisms.
Bokhari et al found that among patients with CAD, the homocysteine level correlates independently with left ventricular systolic function.The mechanism is unknown, but it may be due to a direct toxic effect of homocysteine on myocardial function separate from its effect on coronary atherosclerosis.
Although in multiple observational studies elevated plasma homocysteine levels have been positively associated with increased risk of atherosclerosis, randomized trials have not been able to demonstrate the utility of homocysteine-lowering therapy. In the Heart Outcomes Prevention Evaluation (HOPE) 2 trial, supplements combining folic acid and vitamins B6 and B12 did not reduce the risk of major cardiovascular events in patients with vascular disease.Similarly, in the trial of Bonaa et al treatment with B vitamins did not lower the risk of recurrent cardiovascular disease after acute myocardial infarction.
Possible pregnancy complications secondary to maternal folate status may include spontaneous abortion, abruption placentae, congenital malformations (eg, neural tube defect), and severe language delay in the offspring. In a literature review, Ray et al examined 8 studies that demonstrated association between hyperhomocystinemia and placental abruption/infarction.Folate deficiency also was a risk factor for placental abruption/infarction, although less statistically significant.
Several observational and controlled trials have shown that neural tube defects can be reduced by 80% or more when folic acid supplementation is started before conception. In countries like the United States and Canada, the policy of widespread fortification of flour with folic acid has proved effective in reducing the number of neural tube defects.
Although the exact mechanism is not understood, a relative folate shortage may exacerbate an underlying genetic predisposition to neural tube defects.
In a prospective observational study in Norway, where food is not fortified with folic acid, lack of supplementation with folic acid from 4 weeks before to 8 weeks after conception was associated with increased risk of severe language delay in the child at age 3 years.No association between folic acid supplementation and gross motor skills was reported.
Effects on carcinogens
Diminished folate status is associated with enhanced carcinogenesis. A number of epidemiologic and case-control studies have shown that folic acid intake is inversely related to colon cancer risk.With regard to the underlying mechanism, Blount et al showed that folate deficiency can cause a massive incorporation of uracil into human DNA leading to chromosome breaks.Another study by Kim et al suggested that folate deficiency induces DNA strand breaks and hypomethylation within the p53 gene.
Effects on cognitive function
Several studies have shown that an elevated homocysteine level correlates with cognitive decline. In Herbert's classic study in which a human subject (himself) was in induced folate deficiency from diet restriction, he noted that CNS effects, including irritability, forgetfulness, and progressive sleeplessness, appeared within 4-5 months. Interestingly, all CNS symptoms were reported to disappear within 48 hours after oral folate intake.
Low folate and high homocysteine levels are a risk factor for cognitive decline in high-functioning older adults and high homocysteine level is an independent predictor of cognitive impairment among long-term stay geriatric patients.
Mechanistically speaking, current theory proposes that folate is essential for synthesis of S- adenosylmethionine, which is involved in numerous methylation reactions. This methylation process is central to the biochemical basis of proper neuropsychiatric functioning.
Despite the association of high homocysteine level and poor cognitive function, homocysteine-lowering therapy using supplementation with vitamins B-12 and B-6 was not associated with improved cognitive performance after two years in a double-blind, randomized trial in healthy older adults with elevated homocysteine levels.
Women who are pregnant are at higher risk of developing folate deficiency because of increased requirements.
Elderly people also may be more susceptible to folate deficiency in light of their predisposition to mental status changes, social isolation, low intake of leafy vegetables and fruits, malnutrition, and comorbid medical conditions. The greatest risk appears to be among low-income populations and institutionalized elderly people and less risk among the free-living elderly population.
Folic acid is a coenzyme necessary for the synthesis of thymidine, which is required for DNA synthesis. The major nutritional source is vegetables. It is rapidly absorbed in the jejunum and transported from plasma into storage sites (primarily liver). The daily requirement is about 400 ug. There has been considerable interest recently in the importance of folic acid as a nutrient. Much attention has been given to the role of folic acid in the prevention of neural tube defects, as well as to the relationship between low serum folate levels and an increased risk of fatal coronary heart disease. However, the current primary use of folate assays remains the initial investigation of patients with macrocytic anemia.
What Is Serum Folate?
Serum folate refers to how much folate is in a person’s blood serum. Testing for folate is done by a physician or other qualified health care practitioner. Testing involves drawing blood to find out how much of this essential vitamin is present in the serum, as well as how much of it is present in the red blood cells. Serum folate measurements specifically give doctors an indication of how much folate was recently introduced to the body, whereas folate found and measured in the red blood cells tells doctors how much folate has been stored in the body for long-term use.
Measuring serum folate levels is important, as doing so helps determine whether a person has an elevated serum folate presence or whether a person is suffering from a folate deficiency. Both of these conditions are potentially hazardous to a person’s health and, therefore, should be monitored, particularly if a person is taking folate supplements. While most people’s folate levels are fine when the vitamin is gained from natural sources, individuals who supplement with folic acid vitamins are more likely to have elevated folate levels, which can mask a vitamin B12 deficiency. Individuals with a past history of alcohol abuse or who are anemic are more likely to have a folate deficiency.
Folate is a B vitamin naturally found in foods like broccoli, turnip greens, eggs, yeast, dried beans and citrus fruits. When a synthetic form of folate is used as a vitamin supplement or to fortify foods, such as bread and cereal, it is referred to as folic acid. Folate is an ingredient needed in DNA and RNA to make new cells and to stop existing cells from mutating into diseases like cancer. Folate also helps maintain proper homocysteine levels, which help keep amino acids at optimal levels within the body.
After testing a person’s serum folate levels, if a doctor discovers a deficiency, a person will be advised to take folic acid supplements. Deficiency has an adverse affect on the body and can impede a child’s growth, or cause anemia, heart palpitations or heart disease in adults. When serum folate levels are too high, however, it can trigger seizures in people with epilepsy. Elevated folate levels may also mask the symptoms of a vitamin B12 deficiency, which include neuropathy, dementia and megaloblastic anemia. When these symptoms are hidden by elevated serum folate levels, there is a delay in treating them, which may lead to long-term damage.
What Is the Difference Between Folate and Folic Acid?
Folate and folic acid are two versions of the vitamin B9. While folate is found naturally in the diet, folic acid is man-made and is included in enriched foods as well as vitamin supplements. Folic acid is essential for the body’s growth and development, especially during pregnancy. A deficiency of this vitamin may result in anemia.
Folate and folic acid are both vitamin B9 and are used by the body for the same purpose. Folate, however, can be obtained from green, leafy vegetables, such as spinach, broccoli and lettuce as well as from other foods like okra, bananas, melons, and legumes. Folic acid is man-made and is often added to certain foods, such as grains, cereals, and baked goods, along with other vitamins. It is much easier for the body to absorb than folate because folate must first be converted into folic acid. Folic acid can also be obtained through vitamin supplements.
It is recommended that adults consume 400 micrograms of folate and folic acid daily. The recommendation is higher, especially for pregnant women, who should take 600 micrograms per day during pregnancy and 500 micrograms per day when breast feeding. The daily maximum dosage of folic acid is 1000 micrograms per day for adults, including breastfeeding women.
One of the major functions of folate and folic acid is its role in metabolizing amino and nucleic acids in the body. It is also involved in creating new cells and in growth and development, which is why it is considered especially important during pregnancy. Low levels of folic acid during pregnancy can damage the fetus, causing neural tube defects. Examples of this type of defect include brain and spinal cord problems that can affect an infant long-term. Folate and folic acid are particularly important during the first few weeks of pregnancy.
A deficiency of folate and folic acid can cause problems other than for pregnant women. Folic acid deficiency may cause anemia, resulting in symptoms of weakness, fatigue and shortness of breath. A deficiency of this kind is usually due to not consuming the correct foods. Alcoholics are especially prone to folic acid deficiency, as they typically have an overall low food intake.
Folic Acid Test
A folic acid test measures the amount of folic acid in the blood. Folic acid is one of many B vitamins. The body needs folic acid to make red blood cells (RBC), white blood cells (WBC), platelets, and for normal growth. Folic acid also is important for the normal development of a baby (fetus).
Folic acid can be measured in the liquid portion of blood (plasma). This reflects a person's recent intake of folic acid in the diet. Folic acid is found in foods such as liver; citrus fruits; dark green, leafy vegetables (spinach); whole grains; cereals with added B vitamins; beans; milk; kidney; and yeast.
Folic acid can also be measured as the amount in the red blood cells. This test may be a better way than the plasma test to measure the amount of folic acid stored in the body. The amount of folic acid in red blood cells measures the level when the cell was made, as much as 2 months earlier. This level is not usually affected by the amount of folic acid in your diet each day. It is a more accurate way to measure the body's level of folic acid.
Women who are pregnant or planning to become pregnant need extra folic acid to make more red blood cells and maintain normal growth of their baby. Women who do not get enough folic acid before and during pregnancy are more likely to have a child born with a birth defect, such as a cleft lip or cleft palate or a neural tube defect, such as spina bifida.
Folic acid deficiency can result in a type of anemia called megaloblastic anemia. Mild folic acid deficiency usually does not cause any symptoms. Severe folic acid deficiency may cause a sore tongue, diarrhea, headaches, weakness, forgetfulness, and fatigue.
Folate is also known as folic acid and vitamin B9. Its molecular formula is C19 H19 N7 O6.
Folic acid itself is not biologically active, but its biological importance is due to tetrahydrofolate and other derivatives after its conversion from dihydrofolic acid in the liver.
Folate is found in food in polyglutamyl forms; different types of food contain different numbers of glutamic. The polyglutamyl form of folate is hydrolyzed to a monoglutamyl form (the absorbable form) by the enzyme folate conjugase, which is found mainly in the brush border of the intestinal mucosal cells. This enzyme is also found within cells.
Dihydrofolate is then reduced in the liver by the enzyme dihydrofolate reductase to tetrahydrofolate, which is essential for de novo purine and thymidylate synthesis in the cells as a part of synthesis and repair of DNA .
Folate is usually found in the following foods:
- Meats: Liver, chicken, kidney, egg yolk
- Legumes: Dried beans, lentils, soya products, almonds, nuts
- Starches: Whole-grain breads, wheat flour, potatoes
- Fruit and vegetables: Spinach, beetroot, Brussel sprouts, broccoli, cabbage, asparagus, banana, oranges, peaches
Normal folate requirements are about 200-400 µg/day. The requirement in pregnant and lactating individuals increases to 500-800 µg/day.
Healthy individuals have about 500-20000 µg of folate stored, mainly in the liver.
Folate - test
Testing the folate level, which is also known as folic acid and vitamin B9, is primarily used in the diagnosis of megaloblastic anemia.
The reference range of the plasma folate level varies by age, as follows:
- Adults: 2-20 ng/mL, or 4.5-45.3 nmol/L
- Children: 5-21 ng/mL, or 11.3-47.6 nmol/L
- Infants: 14-51 ng/mL, or 31.7-115.5 nmol/L
The reference range of the red blood cell (RBC) folate level also varies by age, as follows:
- Adults: 140-628 ng/mL, or 317-1422 nmol/L
- Children: Over 160 ng/mL, or over 362 nmol/L
The plasma folate level is very sensitive to dietary changes; it reflects the short-term balance of folate and can decline after few days of fasting, even when folate stores are normal. Conversely, the plasma folate level can be restored to normal with one folate-rich meal.
The RBC folate level is less affected by recent dietary changes; it reflects tissue folate adequacy better than the plasma folate level, since it reflects a time-averaged value of folate. However, measuring the RBC folate level is not entirely free of limitations. Results may be reported as falsely low, especially in pregnancy and alcoholism, as well as in vitamin B12 deficiency. Cellular uptake of folate requires vitamin B12, so vitamin B12 deficiency can decrease RBC folate levels and increase the plasma folate levels.
A plasma folic acid level of more than 4 ng/mL can rule out folate deficiency.
In the absence of recent anorexia or fasting, a plasma folic acid level of less than 2 ng/mL is diagnostic of folate deficiency.
In the following cases, additional tests are indicated for accurate diagnosis, including RBC folate, methylmalonic acid, and homocysteine:
- Plasma folic acid level of 2-4 ng/mL
- Plasma folic acid level of less than 2 ng/mL in the presence of recent anorexia or fasting
- Suspected combined folate and vitamin B12 deficiency
Causes of folate deficiency include the following:
- Decreased folate intake
- Alcohol use
- Advanced age
- Poor dietary intake
- Overcooked food
- Malabsorption: Alcoholism, inflammatory bowel disease, celiac disease, infiltrative disease, short-bowel syndrome
- Increased folate demand: Lactation, pregnancy, exfoliative dermatitis, hemodialysis, chronic hemolysis, leukemias, hypothyroidism
- Medications: Methotrexate, trimethoprim, phenytoin, antimalarials, antacids, oral contraceptives
The following are causes of increased folate levels:
- Blind loop syndrome
- Vegetarian diet
- Pernicious anemia
- Vitamin B12 deficiency (vitamin B12 deficiency can cause increased plasma and decreased RBC folate levels, as it causes decreased cellular uptake)
The main indication for folate testing is in the workup of megaloblastic anemia and hypersegmented neutrophils.
Pregnancy is not an indication for routine folate screening, although it is an indication for prophylactic folate supplementation.
Folate deficiency is treated with folic acid supplementation and management of the underlying cause.
The main presentation of folate deficiency is megaloblastic anemia without neurologic changes, in contrast to vitamin B12 deficiency, in which neurologic changes may be observed.
Folic acid can partially reverse some of the hematologic abnormalities of vitamin B12 deficiency but not the neurologic manifestation. Thus, megaloblastic anemia is not treated with folic acid until vitamin VB12 deficiency is excluded.
Folate deficiency can also cause congenital neural tube defects, the incidence of which is reduced by the administration of folic acid supplements in pregnant women.
The fact that folic acid is required for synthesis and repair of DNA makes it a target for many cancer medications.
Folate deficiency may increase methotrexate toxicity.
A meta-analysis published in 2010 failed to find a statistically significant cancer risk due to folic acid supplements.
Why It Is Done
A folic acid test may be done to:
- Check for anemia. A folic acid test is often done at the same time as a test for vitamin B12 levels because a lack of either vitamin may cause anemia.
- Check for malnutrition or problems absorbing (malabsorption) folic acid.
- See if treatment for folic acid deficiency or vitamin B12 deficiency is working.
- See if a woman has enough folic acid to prevent certain birth defects and allow her baby to grow normally.
How To Prepare
For the folic acid plasma test, do not eat or drink (other than water) for 8 to 10 hours before the test. If you take any medicines regularly, your doctor will talk to you about how to take these before the test.
You do not need to do anything before having a folic acid red blood cell test.
How It Is Done
The health professional drawing blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure to the site and then a bandage.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
A folic acid test measures the amount of folic acid in the blood.
The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Folate in liquid portion (plasma) of blood
3-13 nanograms per milliliter (ng/mL)
7-30 nanomoles per liter (nmol/L) (SI units)
Folate in red blood cells
317-1422 nmol/L (SI units)
More than 160 ng/mL
More than 362 nmol/L
- High levels of folic acid in the blood may mean that you eat a diet rich in folic acid, take vitamins, or take folic acid pills. Consuming more folic acid than the body needs does not cause problems.
- High folic acid levels can also mean a vitamin B12 deficiency. Body cells need vitamin B12 to use folic acid. So if vitamin B12 levels are very low, folic acid cannot be used by the cells, and high levels of it may build up in the blood. But a folic acid test is not a reliable way to test for a vitamin B12 deficiency.
- Low folic acid levels can mean you have a problem with your diet, alcohol dependence, or an eating disorder such as anorexia nervosa.
- Low folic acid levels can also mean you have a problem absorbing or using folic acid, such as a vitamin C deficiency, liver disease, celiac disease, sprue, or Crohn's disease.
- Low folic acid levels can cause problems for certain people. For example:
- A pregnant woman needs extra folic acid for her growing baby.
- People who have hemolytic anemia, a condition that causes the fast destruction of red blood cells, need more folic acid to make more red blood cells.
- People with certain conditions, such as kidney failure and some types of cancer, may use up folic acid quickly. They may need their blood to be cleaned using a machine (kidney dialysis).
What Affects the Test?
Reasons you may not be able to have the test or why the results may not be helpful include:
- Taking some medicines that can affect folic acid levels. Tell your doctor all of the medicines that you take.
- Using too much alcohol.
- Having conditions such as vitamin B12 anemia or iron deficiency anemia.
What to Think About
- Eat a healthy, balanced diet to get the daily recommended intake of folic acid to prevent folic acid deficiency anemia. Many foods have folic acid, such as citrus fruits, leafy green vegetables, and vitamin-fortified cereals.
- You might need to take a folic acid supplement if you have anemia and cannot get enough folic acid from food. Your doctor can tell you if you need to take a supplement.
- Taking folic acid before and during pregnancy can lower the chance of having a baby with a birth defect.
- The folic acid test is often done at the same time as a test for vitamin B12. For more information, see the topic Vitamin B12.
The term folate refers to all derivatives of folic acid. For practical purposes, serum folate is almost entirely in the form of N-(5)-methyl tetrahydrofolate.
Approximately 20% of the folate absorbed daily is derived from dietary sources; the remainder is synthesized by intestinal microorganisms. Serum folate levels typically fall within a few days after dietary folate intake is reduced and may be low in the presence of normal tissue stores. RBC folate levels are less subject to short-term dietary changes.
Significant folate deficiency is characteristically associated with macrocytosis and megaloblastic anemia. Lower than normal serum folate also has been reported in patients with neuropsychiatric disorders, in pregnant women whose fetuses have neural tube defects, and in women who have recently had spontaneous abortions.(3) Folate deficiency is most commonly due to insufficient dietary intake and is most frequently encountered in pregnant women or in alcoholics.
Other causes of low serum folate concentration include:
-Excessive utilization (eg, liver disease, hemolytic disorders, and malignancies)
-Rare inborn errors of metabolism (eg, dihydrofolate reductase deficiency, forminotransferase deficiency, 5,10-methylenetetrahydrofolate reductase deficiency, and tetrahydrofolate methyltransferase deficiency)