Folate, the natural form of the vitamin also supplied as folic acid, comes from green vegetables, legumes and fortified grain and is absorbed in the upper small intestine. It is needed for DNA synthesis and cell division, so tissues that renew quickly — bone marrow above all — depend on it, and it also feeds the pathway that clears homocysteine. Serum folate is measured chiefly in the work-up of anaemia with large red cells.
No readings for this marker yet.
Low values most often reflect a diet poor in fresh vegetables, heavy alcohol use, malabsorption from coeliac disease, or increased demand in pregnancy; certain drugs, including methotrexate and trimethoprim, interfere with folate metabolism. Higher-than-usual values usually come from supplements or fortified food and carry little meaning on their own, though they can obscure an underlying B12 problem. A single low result is a prompt to repeat the test and review diet and medicines with a doctor.
Serum folate responds quickly to recent meals and to a supplement taken the day before, so it can look normal despite depleted stores; red cell folate reflects the longer-term picture. Alcohol lowers it, and haemolysis of the sample falsely raises it, since red cells are folate-rich. Vitamin B12 is measured with it because the two produce an identical marrow picture, and homocysteine rises when either is short.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.