Austin J Nutri Food Sci.2015;3(1): 1055.
Recommended use of Cut-off Folate Concentrations in Serum and Erythrocyte (Red Blood Cell) as Expressed by Folic Acid Equivalent for the Diagnosis of Deficiency in Deliberating the Creation of Dietary Reference Intakes
Ihara H1*, Hirota K2, Watanabe T3, Totani M4, Hashizume N5, Aoki Y6, Nagamura Y7, Kamioka K8, Onda K8, Sunahara S8, Suzuki T9, Itabashi M9, Ishibashi M10, Ito S11, Ohashi K12, Ohta Y13, Nobori T14, Fujishiro K15, Maekawa M16, Miura M17, Miyano H18, Ando T18 and Nishimura K19
1Faculty of Science, Toho University/Faculty of Risk and Crisis Management, Chiba Institute of Science, Japan
2Information Center, National Institute of Health and Nutrition, Japan
3Department of Dietary Environment Analysis, University of Hyogo, Japan
4Graduate School of Human Life Science, Showa Women’s University, Japan
5Department of Health and Nutrition, University of Human Arts and Sciences, Japan
6Kanagawa Health Service Association, Japan
7Department of Clinical Nutrition, Suzuka University of Medical Science, Japan
8LSI Medience Corporation, Japan
9SRL, Inc., Japan
10Department of Laboratory Medicine, New Tokyo Hospital, Japan
11Department of Clinical Laboratory Sciences, Nitobe Bunka College, Japan
12Department of Clinical Chemistry, Fujita Health University, Japan
13Department of Chemistry, Fujita Health University,Japan
14Department of Molecular and Laboratory Medicine, Mie University Graduate School of Medicine, Japan
15Kyowa Medex Co., Ltd., Japan
16Department of Laboratory Medicine, Hamamatsu University School of Medicine, Japan
17Faculty of Pharmaceutical Sciences, Hokuriku University, Japan
18Ajinomoto Co., Inc., Japan
19Beckman Coulter Japan Co., Japan
*Corresponding author: Hiroshi Ihara, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan/Faculty of Risk and Crisis Management, Chiba Institute of Science, 15-8 Shiomi, Choshi, Chiba 288-0025, Japan
Received: January 07, 2015; Accepted: January 19,2015; Published: January 19, 2015
Dietary Reference Intakes (DRIs) for folate in the US, Canada and Japan have been decided based on the dietary amounts of folate in populations in whom erythrocyte (Red Blood Cell: RBC) folate concentrations were higher than the cutoff value of 300 nmol/L (mass concentration of 140 ng/mL). This mass concentration was expressed as equivalent to 5-methyltetrahydrofolate.
We read an interesting new WHO technical consultation on folate and vitamin B12 deficiencies  describing cutoff values that indicated deficiency. The cutoff values were < 10 nmol/L (4 ng/mL) for serum folate, < 340 nmol/L (151 ng/mL) for RBC folate, and < 150 pmol/L (203 pg/mL) for plasma vitamin B12. These values were the lowest concentrations of serum and RBC folate capable of repressing an exponential increase in plasma homocysteine, and of serum vitamin B12 capable of repressing an exponential increase in serum methylmalonic acid . We created Dietary Reference Intakes (DRIs) for folate in Japan in 2000  with the use of a previous cutoff value from WHO that indicated 7 nmol/L (3 ng/mL ) of serum folate for deficiency . The DRIs created were revised in 2010 with the use of RBC folate (300 nmol/L; 138 ng/mL rounded to 140 ng/mL) obtained from US and Canadian DRIs .
Upon closer reading of WHO technical consultation, we realized that both the cutoff mass concentrations for serum and RBC folate were expressed as equivalent to folic acid (FA: molecular mass of 441.40 Da). In the US and Canadian DRIs, however, the mass concentration of RBC folate was expressed as equivalent to 5-methyltetrahydrofolate (5-MTHF: molecular mass of 459.46 Da). In our previous study  as well as other studies [7-9], the mass concentrations of serum folate were permitted to be expressed as equivalent to FA for the international standardization of serum folate measurement.
For the standardization of RBC folate measurement, WHO developed a new standard (IS 03/178) in 2006 [7,8], and its assigned values were determined by the Reference Measurement Procedure (RMP) using a Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). Since IS 03/178 could be used as a calibration material for both measurements of serum and RBC folate, WHO proposed a way to use IS 03/170 independently from their previous international standard for RBC folate (IS 95/528) . The IS 95/528 had an assigned value of the mass concentration for RBC folate, but the molar concentration related to FA or 5-MTHF was not defined. Furthermore, its mass concentration was a mean value (e.g., consensus value) calculated from data collected from 13 laboratories employing different methods and different standards comprised of 5-MTHF and/or FA.
Nowadays, both serum and RBC folate are determined by automated methods; however, the assay values of serum total folate (the sum of all folate vitamers including 5-MTHF and FA) in not all of the automated methods, are expressed as equivalent to FA as we previously reported . While, the assay values of RBC folate in the automated methods (some of which used IS 95/528 as a calibrator) were not clearly disclosed by the manufacturers, whether they are expressed as equivalent to FA or 5-MTHF. When 340 nmol/L of RBC folate is expressed as equivalent to FA and 5-MTHF, its mass concentrations related to FA and 5-MTHF are calculated to be 150 and 156 ng/mL, respectively. Even using mass concentration of either FA or 5-MTHF bias was negligibly small in the nutritional assessment, but was considerably different in deliberating the creation of DRIs. Therefore, in the US and Canadian DRIs, as well as in the Japanese DRIs, we recommend that the FA equivalent mass concentrations for serum and RBC folate be used as measured by the automated methods related to IS 03/178 (not IS 95/528).
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