Folate, RBC

Whole blood (two tubes)

Two full lavender-top (EDTA) tubes

Verify that the patient has not had vitamins containing folic acid during the previous three to five days; if so, consult physician.

Detect folate deficiency; monitor therapy with folate; evaluate megaloblastic and macrocytic anemia

Folate assays of samples from patients receiving therapy with certain pharmaceuticals (eg, methotrexate or leucovorin), are contraindicated because of the cross-reactivity of folate binding protein with these compounds.¹

As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposes.¹ In rare cases, interference due to extremely high titers of antibodies to streptavidin and ruthenium can occur.¹ The test contains additives that minimize these effects.

Electrochemiluminescence Immunoassay (ECLIA)

>498 ng/mL

Folates are compounds of pteroylglutamic acid (PGA) that function as coenzymes in metabolic reactions involving the transfer of single-carbon units from a donor to a recipient compound. Folate, with vitamin B₁₂, is essential for DNA synthesis, which is required for normal red blood cell maturation.² Humans obtain folate from dietary sources including fruits, green and leafy vegetables, yeast, and organ meats.³ Folate is absorbed through the small intestine and stored in the liver.

Low folate intake, malabsorption as a result of gastrointestinal diseases, pregnancy, and drugs such as phenytoin are causes of folate deficiency.⁴ Folate deficiency is also associated with chronic alcoholism.⁵ Folate and vitamin B₁₂ deficiency impair DNA synthesis, causing macrocytic anemias. These anemias are characterized by abnormal maturation of red blood cell precursors in the bone marrow, the presence of megaloblasts, and decreased red blood cell survival.²

Since both folate and vitamin B₁₂ deficiency can cause macrocytic anemia, appropriate treatment depends on the differential diagnosis of the deficiency. Serum folate measurement provides an early index of folate status³; however, folate is much more concentrated in red blood cells than in serum so the red blood cell folate measurement more closely reflects tissue stores.^5,6 Erythrocytes incorporate folate as they are formed, and levels remain constant throughout the life span of the cell. RBC folate levels are less sensitive to short-term dietary effects than are serum folate levels. Red blood cell folate concentration is considered the most reliable indicator of folate status.³

Low serum folate during pregnancy has been associated with neural tube defects in the fetus.^7,8