Folate, RBC

CPT: 82747; 85014
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Test Details

Synonyms

  • Folates RBC (With Hct)

Test Includes

RBC folate; hematocrit

Use

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

Limitations

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.

Methodology

Electrochemiluminescence Immunoassay (ECLIA)

Reference Interval

>498 ng/mL

Additional Information

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

Specimen Requirements

Specimen

Whole blood (two tubes)

Container

Two full lavender-top (EDTA) tubes

Patient Preparation

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

Collection

Transfer 4 mL from one whole blood tube into a plastic transport tube and freeze. Refrigerate second whole blood tube. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

Storage Instructions

Freeze whole blood transport tube and refrigerate whole blood specimen.

Causes for Rejection

No frozen whole blood; no refrigerated whole blood; transport tubes with whole blood for the hematocrit portion

Clinical Information

Special Instructions

This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.

Footnotes

1. Folate on Elecsys 1010/2010 and Modular Analytics E170 [package insert]. 2007-02, V1. Indianapolis, Ind: Roche Diagnostics; 2007.
2. Miale JB. Laboratory Medicine Hematology. St Louis, Mo: CV Mosby;1982:416-440.
3. Brewster MA. Vitamins. In: Kaplan LA, Pesce AJ, eds. Clinical Chemistry: Theory, Analysis, and Correlation. St. Louis, Mo: CV Mosby;1989:543-568.
4. Fairbanks VF, Klee GG. Biochemical aspects of hematology. In: Burtis CA, Ashwood ER, eds. Tietz Textbook of Clinical Chemistry. WB Saunders Co;1999:1642-1710.
5. McNeely MD. Folic acid. In: Pesce AJ, Kaplan LA, eds. Methods in Clinical Chemistry. St Louis, Mo: CV Mosby;1987:539-542.
6. Snow CF. Laboratory diagnosis of vitamin B12 and folate deficiency: A guide for the primary care physician. Arch Intern Med. 1999 Jun 28; 159(12):1289-1298. 10386505
7. Wolff T, Witkop CT, Miller T, Syed SB, US Preventive Services Task Force. Folic acid supplementation for the prevention of open neural tube defects: An update of the evidence for the US Preventive Services Task Force. Ann Intern Med. 2009 May 5; 150(9):632-639. 19414843
8. McNulty H, Cuskelly GJ, Ward M. Response of red blood cell folate to intervention: Implications for folate recommendations for the prevention of neural tube defects. Am J Clin Nutr. 2000 May; 71(5 Suppl):1308S-1311S. 10799407

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
266015 Folate, RBC 266019 Folate, Hemolysate ng/mL 2282-2
266015 Folate, RBC 005058 Hematocrit % 4544-3
266015 Folate, RBC 266022 Folate, RBC ng/mL 2283-0

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