Synonyms: Folate
Related tests: Homocysteine, full blood count
Clinical significance
Folic acid (pteroylglutamic acid) takes its name from being found, mainly as polyglutamates, in some broad-leaved vegetables. After the polyglutamates are hydrolysed in the digestive tract, it is absorbed in the proximal jejunum.
The daily requirement ranges from 50 to 100 micrograms. The liver stores are very limited and can quickly run out if dietary intake is poor.
Folic acid plays an essential role in the synthesis of purine and pyrimidine bases, so a deficiency leads to reduced DNA synthesis. Folic acid is also involved in the synthesis of the amino acid methionine from homocysteine in the presence of vitamin B12.
Folic acid deficiency causes megaloblastic anaemia because of the reduced production of cells with a rapid turnover, such as those of the blood-forming line.
Folic acid deficiency can be due to increased requirements (pregnancy, breastfeeding, growth, tumours, infections), reduced dietary intake (malnutrition, alcoholism) or malabsorption (coeliac disease, sprue, inflammatory bowel disease, bowel resection).
In the first months of pregnancy, a daily folic acid supplement is very useful in preventing neural tube defects (anencephaly, spina bifida).
Clinical indications
Megaloblastic anaemia due to deficiency, pregnancy, drug treatment (methotrexate), malabsorption, alcoholism, hyperhomocysteinaemia.
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
Notes
Folic acid antagonists: methotrexate, triamterene, trimethoprim, pyrimethamine; medicines that reduce folic acid absorption: acetylsalicylic acid, anticonvulsants, isoniazid, oral contraceptives, metformin, antacids, colestyramine.
In patients with megaloblastic anaemia due to folate deficiency, serum vitamin B12 levels should also be assessed.