We assessed total antioxidant capacity using three different methods, in plasma samples treated with either EDTA or heparin as anticoagulant, from 26 healthy subjects. Total antioxidant capacity was determined using an oxygen electrode (as the total peroxyl radical-trapping antioxidant parameter), by enhanced chemiluminescence, and by measurement of the antioxidant-mediated quenching of the absorbance of a radical cation. The choice of anticoagulant had a profound effect on antioxidant capacity with heparinized plasma giving consistently higher values than plasma anticoagulated with EDTA. Using the oxygen electrode the mean value was 786.5 ± 171.5 μmol/L (heparin) compared to 681.4 ± 160.4 μmol/L (EDTA, P < 0.01). The chemiluminescence technique gave a mean antioxidant capacity of 915.6 ± 214.1 μmol/L in heparin samples and 714.4 ± 195.4 μmol/L in EDTA samples (P < 0.0001). The absorbance quenching technique gave a mean value of 867.0 ± 199.2 μmol/L (heparin) and 675.5 ± 245.4 μmol/L (EDTA, P < 0.001). All methods tested showed comparable results for EDTA plasma, but the chemiluminescence technique gave higher apparent antioxidant capacity than either of the other two techniques when heparin plasma was used. We suggest that either heparin is interacting to enhance antioxidant protection perhaps through release of superoxide dismutase, or the chelation of metal ions by EDTA is limiting the activity of antioxidant metalloenzymes. Consistency in the choice of anticoagulant is clearly extremely important.
- Ethylenediaminetetra-acetic acid (EDTA)
- Free radicals