Influence of 5,10-methylenetetrahydrofolate reductase polymorphism on whole-blood folate concentrations measured by LC-MS/MS, microbiologic assay, and Bio-Rad radioassay

Abstract

BACKGROUND: The 5,10-methylenetetrahydrofolate reductase (NADPH) (MTHFR) C677T polymorphism may affect whole-blood folate pattern measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and total folate measured by LC-MS/MS, microbiologic assay, and Bio-Rad radioassay (BR). METHODS: We analyzed 171 whole blood hemolysates from 2 blood banks for folate pattern and total folate concentrations using these 3 methods and determined MTHFR genotype. RESULTS: The median (range) total folate concentration by LC-MS/MS was higher in the US set [378 (228-820) nmol/L; n = 96] than in the European set [250 (122-582) nmol/L; n = 75]. The whole-blood folate pattern [median (range)] was similar for individuals with C/C (n = 73) and C/T (n = 66) genotype: 88% (71%-91%) and 86% (50%-91%), respectively, for 5-methyltetrahydrofolic acid (5CH3THF) vs 12% (9%-29%) and 14% (9%-51%) for forms other than 5-methyltetrahydrofolic acid (non-5CH3THF). Individuals with T/T (n = 32) genotype had 58% (22%-87%) 5CH3THF vs 42% (13%-78%) non-5CH 3THF. Compared with microbiologic assay results, LC-MS/MS (r = 0.94) and BR (r = 0.87) results were significantly lower (-10% and -45%, respectively); however, these differences were concentration dependent and also genotype dependent for the BR assay (-48% for C/C+C/T and -31% for T/T). The microbiologic assay completely recovered [mean (SD)] folates added to a whole blood hemolysate, except for tetrahydrofolic acid (THF) [46.4% (8.1%)]. The BR assay underrecovered 5CH3THF [51% (4.1%)] and 5-formyltetrahydrofolic acid [18% (0.1%)], and overrecovered THF [152% (19%)]. CONCLUSION: MTHFR C677T polymorphism influences the folate pattern in whole blood. The agreement between total folate by LC-MS/MS and microbiologic assay, independent of the MTHFR genotype, allows the use of one regression equation. Because BR results are genotype dependent, different regression equations should be used.