Folate and folic acid are naturally occurring sources of B-vitamins found in fortified foods, leafy green vegetables, some fruits and legumes. If the body lacks adequate folate, patients may suffer from diarrhea, macrocytic anemia, nerve damage and many other symptoms. Folate deficiency is especially risky for pregnant women. An excess of folate in the diet can mask symptoms of vitamin B12 deficiency but is otherwise relatively harmless.

Patients should get a folate blood test if neuropathy or anemia is suspected, to determine the quality of their diets or to evaluate the effectiveness of treatment for an existing folate or vitamin B12 deficiency. Doctors usually recommend this blood test when a complete blood count (CBC) test shows large red blood cells or abnormal white blood cells. 

This test may also be appropriate for people who have symptoms of anemia but normal iron levels, as well as those who suffer from memory loss, tingling or itching feelings in their extremities, altered mental states or eye twitches. Anyone who is already being treated for a vitamin B12 or folate deficiency should have their blood folate levels checked periodically until it is certain that the treatment is working correctly.

They may also need to discontinue use of folic acid supplements. Some drugs, including alcohol, aspirin, birth control pills, tetracyclines, penicillin, erythromycin, phenobarbitol and malaria drugs may produce an inaccurately low measurement on a folate blood test.