The method involves quantitative conversion of all folate species and their polyglutamates into para-aminobenzoylglutamate (pABG) by oxidation and mild acid hydrolysis, using a slight modification of a method developed and validated for measurement of degraded folate in serum/plasma samples (2, 3). In fresh and adequately handled blood samples there is a strong correlation between RBC folate measured as pABG equivalents and microbiologically active folate (Figure 1).
Lower limit of detection (LOD): 0.25 nmol/L.
Within-day CV: 6-9%; between-day CV: 3-10 %.
Assessment of folate status, based on erythrocyte (RBC) folate measured in blood samples collected without ascorbic acid, exposed to elevated temperature or stored for decades.
The view has prevailed that RBC folate reflects the average folate status over time, corresponding the lifetime of the erythrocytes (about 120 days), and that e-folate is a better indicator than s-folate of folate status in tissues.
Patient/subject: Recent folate intake from supplements or meal is not critical.
Matrix: Whole blood, hemolysate.
Volume: Minimum volume is 60 µL, but 200 µL is optimal and allows reanalysis.
Frozen, on dry ice. (for general instruction on transportation, click here.)
Reported values: >340 nmol/L.
Intraclass correlation coefficients (ICC): na.
1. Hannisdal, R., Ueland, P.M., and Svardal, A. (2009). Liquid chromatography-tandem mass spectrometry analysis of folate and folate catabolites in human serum. Clin Chem 55, 1147-154
2. Hannisdal, R., Svardal, A., and Ueland, P.M. (2008). Measurement of folate in fresh and archival serum samples as p-aminobenzoylglutamate equivalents. Clin Chem 54, 665-672.
3. Hannisdal, R., Gislefoss, R.E., Grimsrud, T.K., Hustad, S., Morkrid, L., and Ueland, P.M. (2010). Analytical recovery of folate and its degradation products in human serum stored at -25 degrees C for up to 29 years. J Nutr 140, 522-26.
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Amino acids: Alanine, Arginine, Asparagine, Aspartic acid, Glutamic acid, Glutamine, Glycine, Histidine, Isoleucine, Kynurenine, Leucine, Lysine, Methionine, Ornithine, Phenylalanine, Proline, Sarcosine, Serine, Threonine, Total cysteine, Tryptophan, Tyrosine, Valine
Amino acids and catabolites: 2-Aminoadipic acid, 2-Hydroxybutyrate, 3-Hydroxysiobutyrate, α-Hydroxyglutaric acid, β-Alanine, β-Aminoisobutyrate, β-Hydroxy B-methylbutyric acid, Phenylacetylglutamine
Acylcarnities: BB, C0, C2, C3, C3, DC, C4, C4-OH , C4-DC , iC5 , C5-DC, C5:1 , C6 , C8, C10, C12, C14 , C14-OH, C16, C16-OH, C18 , C18-OH, C18:1, C18:2
TCA metabolites: α-Ketoglutarate, Citrate, Fumarate, Isocitrate, Lactate, Malate, Pyruvate, Ketone bodies, 3-Hydroxybutyrate, Acetoacetate
AGEs: Carboxyethyllysine, Carboxymethyllysine
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Kynurenines: Kynurenine, Kynurenic acid, Quinaldic acid, Anthranilic acid, 3-Hydroxykynurenine, Xanthurenic acid, 3-Hydroxyanthranilic acid, Picolinic acid, Quinolinic acid, Nicotinic acid, Nicotinamide, N1-methylnicotinamide
Neopterin
Proteins: C-Reactive protein, Calprotectin, Serum Amyloid A
Ratio-derived: Kynurenine/tryptophan ratio, PAr index (PLP, PL, PA)
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SCFAs: Acetate, Butyrate, Formate, Isobutyrate, Isovalerate, Propionate, Valerate, α-Methylbutyrate
Indoles: 3-Indoxyl sulfate, Imidazole propionate, Indole-3-acetamide, Indole-3-acetate, Indole-3-aldehyde, Indole-3-lactate, Indole-3-propionate
Choline metabolites: Choline ,Betaine, DMG, TMAO
Amino acid derived: Phenylacetylglutamine
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B-vitamins, functional markers, and methyl donors: 4-Pyridoxic acid, Betaine, Choline, Cobalamin, Flavin mononucleotide, Folate, Methylmalonic acid, N1-methylnicotinamide, Nicotinamide, Nicotinic acid, Pyridoxal, Pyridoxal 5-phosphate, Pyridoxine, Riboflavin, Thiamine, Thiamine monophosphate, Total homocysteine
Fat-soluble vitamins: 25-hydroxy vitamin D2, 25-hydroxy vitamin D3, α-Tocopherol (Vit. E), All-trans retinol (Vit. A), Phylloquinone (Vit. K1), y-Tocopherol (Vit. E)
Essential amino acids: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine
Meat and fish intake: 1-Methylhistidine, 3-Methylhistidine, B-Alanine, Creatine, Creatinine, TMAO
Tobacco use and coffee intake: Cotinine, Trans-3-hydroxycotinine, Trigonelline
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