The assay of ascorbic acid in serum is not affected by physiological concentrations of transferrin and hemoglobin.

Transferrin and hemoglobin have been reported to oxidize L-ascorbic acid (AA) in vitro. The aim of this study was to determine whether or not physiological concentrations of serum transferrin (reference range 22-45 micromol/L) and hemoglobin (reference range 0-3.0 micromol/L) interfer with the measurement of AA in the serum. Transferrin (33 to 41 micromol/L) and hemoglobin (1.9 micromol/L) added to freshly pooled serum significantly decreased measured AA in the serum (p < 0.05). However, we found that the magnitude of the decrease in AA due to transferrin at concentrations within the reference range or up to 80 micromol/L was inconsequential, and had no clinical importance in diagnosing a low AA concentration. Hemoglobin at concentrations within the reference range had little affect on the serum AA measurement. However, when serum specimens were stored at 4 degrees C for more than 1.5 h, the magnitude of the decrease in AA due to hemoglobin at physiological concentrations may cause a misleading clinical diagnostic evaluation of low AA concentration.