Folic acid [also known a folate, folactin, or pterogylglutamic acid (PGA)] is a heat-labile, water soluble vitamin. A deficiency of this vitamin leads to a megaloblastic anemia similar to vitamin B12 deficiency anemia. This deficiency is relatively uncommon, but occurs with a greater frequency that of vitamin B12 deficiency. This is due in part to the smaller stores of folate. Folate deficiency anemia is found primarily in alcoholics, chronic diseases, and those individual who have very poor dietary habits with little or no meat and leafy green vegetables. This deficiency is designated as a macrocytic, normochromic anemia.
When folic acid is absorbed across the intestine, it is first hydrolyzed, then reduced, and finally methylated to form methyltetrahydrofolate (CH3THF). Although there are other biologically active forms of folate, methylthetrahydrofolate is the vitamin that enters the cell. It has an important role in the synthesis of DNA.
Laboratory findings include the following:
-  Serum folate is less than 3 μg/L
- Erythrocyte folate is less than 100 μg/L
-  Blood cell differential:A. Presence of macrocytes B. Anisocytosis and poikilocytosis C. Basophilic stippling may be present (also Howell-Jolly Bodies and Cabot rings)
-  WBC counts may vary from 1,000 to 6,000/μL. A. Neutropenia with hypersegmentation (Note: Neutrophils may be larger than normal. Such cells are called macropolycytes.) B. Lymphocytosis
-  The reticulocyte count may vary from 1.5% to 8.0%
-  The RBC count may vary from a low of one million/μL to normal.
-  The platelet count may be decreased.