BEVITAL AS

Targeted Metabolomics Services

Folate in blood cells

Updated 21/12/2022

What is measured?

Synonyms: e-folate, erythrocyte folate, RBC-folate.
Method(s): Microbiological assay, using a chloramphenicol-resistant strain of Lactobacillus casei (1). The assay has been adapted to a microtiter plate format and is carried out by a robotic workstation. Notably, samples containing antibiotic(s) that inhibit(s) the growth of Lactobacillus casei may cause assay interference.
What is measured: Biologically active folate species in blood cells. In the cells, about 50 different folate species exist, with variable polyglutamate chain length.

Methodological concern

Methods for measurement of e-folate include hemolysate preparation that is difficult to control. First, the various folate species are deconjugated to monoglutamate forms prior to detection. This reaction is catalyzed by endogenous deconjugase, is pH sensitive and difficult to standardize. The various monoglutamates that are formed support the growth of Lactobacillus casei to a variable extent (and show different affinity to folate binders used in competitive binding assays). Besides, distribution between the different folate species is related to the MTHFR 677C->T genotype.
These are the main reasons that values for e-folate show large variation between laboratories, between different assay formats, and that the CVs are usually high. The calibrators used (usually folic acid in aqueous matrix) do not undergo the various steps in the assay, and do not adjust for precipitation, hemolysis, and binding of folates to oxyhemoglobin etc. Finally, folate instability has made external quality control difficult.

Indication(s)

Assessment of folate status.
The view has prevailed that e-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. However, folate status may vary over a shorter time period, and s-folate may better reflect such fluctuation. Besides, total homocysteine is a responsive indicator of folate status in tissues.

Specimen, collection and processing

Patient/subject: Some antibiotics may inhibit growth of Lactobacillus casei, and may cause artificial, low folate levels.
Matrix: Whole blood.
Volume: Minimum volume is 100 µL, but 250 µL is optimal and allows sample handling and reanalysis.
Preparation and stability: Folate in hemolysate is degraded at room temperature, but also in samples frozen at -20 °C. In some samples stored frozen for years, folate is not detected (2).

Transportation

Frozen, on dry ice. (for general instruction on transportation, click here.)

Recommendation

The measurement of e-folate should be abandoned.

Literature

1. Molloy, A.M., and Scott, J.M. (1997). Microbiological assay for serum, plasma, and red cell folate using cryopreserved, microtiter plate method. Methods Enzymol 281, 43-53.
2. Bailey, L.B., Stover, P.J., McNulty, H., Fenech, M.F., Gregory, J.F., Mills, J.L., Pfeiffer, C.M., Fazili, Z., Zhang, M., Ueland, P.M., et al. (2015). Biomarkers of nutrition for development-folate review. J Nutr 145, 1636S-680S.

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Cardiometabolic
Inflammation
Microbiome
Nutrition
Categories

Amino acids, amino acid catabolites, acylcarnitines, TCA metabolites, ketone bodies, AGEs



Kynurenines, ratio-derived metabolites, proteins





SCFAs, indoles, choline metabolites, amino acid derived





B-vitamins, functional markers, and methyl donors, fat-soluble vitamins, essential amino acids, meat & fish intake, tobacco use & coffee intake
Biomarkers (n)
65
19
20
41
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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 acid 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: Acetoacetate, 3-Hydroxybutyrate

AGEs: Carboxyethyllysine, Carboxymethyllysine

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Kynurenines: 3-hydroxykynurenine, 3-hydroxyanthranilic acid, Anthranilic acid, Kynurenine, Kynurenic acid, Nicotinic acid, Nicotinamide, N1-methylnicotinamide, Picolinic acid, Quinaldic acid, Quinolinic acid, Xanthurenic acid

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

Volume (μl)
200
150
250
300
Analytical techniques
GC- and LC-MS/MS
LC- and MALDI-MS
GC- and LC-MS/MS
GC- and LC-MS/MS

Turnaround time

2-6 weeks, depending on number of samples and laboratory capacity.
Please contact us for a projected time estimate specific to your project.

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