Targeted Metabolomics Services

RBC folate as pABG equivalents

Updated 21/12/2022

What is measured?

Synonyms: e-folate, erythrocyte folate, RBC-folate.
Erythrocyte (RBC) folate as pABG equivalents, after oxidation and mild acid hydrolysis.
Method(s): LC-MS/MS (1).


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).

Performance of the assay

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.

Specimen, collection and processing

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

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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