Method(s): LC-MS/MS (1).
What is measured: Serum folate as pABG equivalents, after oxidation and mild acid hydrolysis.
The method involves quantitative conversion of all folate species and their polyglutamates into para-aminobenzoylglutamate (pABG) by oxidation and mild acid hydrolysis (2, 3). In fresh and adequately handled serum/plasma samples there is a strong correlation between serum folate measured as pABG equivalents and microbiologically active folate (2).
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 folate measured in serum/plasma samples exposed to elevated temperature or stored for decades (3).
Specimen, collection and processing
Patient/subject: Serum folate increases after at folate rich meal, and the concentration reflects (in contrast to erythrocyte folate) short-term folate statu.
Matrix: Serum or plasma.
Volume: Minimum volume is 60 µL, but 200 µL is optimal and allows reanalysis.
Transportation; for general instruction on transportation, click here.
Frozen, on dry ice.
Reported values, interpretation
Reported values: >7.5 nmol/L.
Intraclass correlation coefficients (ICC): 0.56.
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.