Observations on the determination of serum and red-cell folate levels by a radiometric assay method.

Our experience with the Bio-Rad "Quanta-Count" folate radioassay kit has revealed very good in-run precision and good day-to-day reproducibility in the assay of both serum and red-cell folate levels. Ascorbic acid is not required as folate preservative if blood samples are frozen within hours after collection. For the determination of red-cell folates, our data clearly show the need for maintenance of a certain level (6-8 gm%) of protein in the assay system. Protein (albumin or folate-free human serum) must be added to the red-cell lysate to compensate for the serum loss resulting from the high dilution factor necessary. In the absence of this added protein, red-cell values are markedly lower. A good correlation exists between red-cell folate values obtained from the assay of washed red cells and from the assay of whole blood with corrections for serum folate levels.