Ferric Reducing Capacity Versus Ferric Reducing Antioxidant Power for Measuring Total Antioxidant Capacity

To compare the performance of the ferric reducing capacity (FRC) assay with the ferric reducing antioxidant power (FRAP) assay to measure the total antioxidant capacity (TAC) of serum samples. Serum from 10 healthy ethnic Chinese adult volunteers was assayed for TAC levels. A Sunrise absorbance reader was used for measurements of absorbance changes. The kinetic force of the reaction was monitored at 2-minute intervals for as long as 10 minutes at room temperature. The difference in absorbance between the blank and sample specimens was calculated. No significant increase in signal was observed at the 2-minute mark for the vitamin C reaction kinetic manifestations of FRC or FRAP. However, over time an increase was observed in absorbance levels in readings with serum. The dose-response lines for both assays showed strong linearity up to the 2000 µmol/L concentration of vitamin C tested at the 4-minute mark. Serum TAC ranged from 264 to 610 µmol/L of vitamin C equivalents for FRC and from 172 to 418 for FRAP. A strong positive correlation was observed between the TAC of the 10 serum samples measured by both assay methods. The FRC assay is a useful alternative to the FRAP assay for measuring the TAC of serum due to its simplicity and speed of use and because it does not require specialized equipment. However, normal ranges should be established in the population intended before our results are put to clinical use.