The Determination of Erythrocyte Folate Concentration Using a Two - Phase Ligand - binding

The concentration of folate in erythrocytes was determined using a two-phase ligandbIndIng radloasuy procedure described previously for measuring serum folate. The mean (± SD) folate concentration In erythrocytes of 20 normal subjects was 210 * 67 ng/mI. In 12 patients clinically folate deficient who had normal serum B2 concentration, the mean (± SD) erythrocyte folate was 71 * 39 ng/ml. Incubation of the lysed erythrocytes for 2 hr prior to boiling increased the radioassayable folate. The radloassayable folate decreased rapidly If the whole blood was stored at 4#{176}C without ascorbate. Extracts of blood prepared with ascorbate could be stored at -20#{176} C for several days. The radloassayable concentration of erythrocyte folate was similar to the values obtained using Lactobacillus case! when the concentration was 200 ng/ ml or less. With values higher by L. case!, the radioassayable folate was significantly lower even though the normal and folatedeficient groups were distinctly separated. This radioassay provides a rapid and reliable method of measuring erythrocyte folate, a parameter which reflects folate stores more reliably than serum folate concentration.