Comparison of spectrophotometric and enhanced chemiluminescent assays of serum antioxidant capacity W. Stephen Waring a, * , Vinita Mishra b , Simon R.J. Maxwell a a Clinical Pharmacology Unit, The University of Edinburgh, Western General Hospital, Porterfield Road, Edinburgh EH4 2XU, Scotland, UK b Department of Clinical Chemistry, Royal Liverpool University Hospital, Liverpool L7 8XP, UK Received 27 February 2003; received in revised form 4 July 2003; accepted 16 July 2003 Abstract Background: Over recent years, interest in total antioxidant capacity measurement in biological fluids has increased. A number of assays are now available, and we wished to compare an enhanced chemiluminescence (ECL) method to a spectrophotometric method, the total antioxidant status (TAS) assay. Methods: Serum urate concentration, ECL and TAS were measured in 34 healthy subjects. Additionally, 10 subjects participated in a two-way, randomised crossover study, and received urate 1000 mg or vitamin C 1000 mg intravenously over 1 h. Serum ECL and TAS were measured at 0, 15, 30, 45, 60, 90 and 120 min after commencing infusion. Results: Baseline measurements were poorly correlated between ECL and TAS assays, and between serum urate concentration and each antioxidant assay. There was good correlation between the change in antioxidant capacity detected by both assays during urate infusion (R = 0.79, p < 0.001, n = 60), but not vitamin C infusion. Conclusions: ECL and TAS measures of serum antioxidant capacity correlate poorly in a healthy population, although both are sensitive to increases in circulating urate concentrations. Therefore, ECL and TAS appear sensitive to different factors. The comparative strengths and weaknesses of various antioxidant assays should be reviewed. D 2003 Elsevier B.V. All rights reserved. Keywords: Total antioxidant status; Uric acid; Ascorbic acid; Randomised controlled trial 1. Introduction Recently, there has been increasing interest in the contribution of free radical-mediated oxidative stress to several disorders, including atherosclerosis, diabe- tes mellitus, and degenerative neurological diseases [1–3]. This has stimulated interest in the role of protective physiological antioxidants, and assay meth- ods used for their quantification. Antioxidants act in various ways to prevent oxidative damage; however, it is scavenging or ‘chain-breaking’ antioxidants that are believed to confer greatest protection, and these in- clude a variety of compounds such as ascorbate, alpha-tocopherol, urate, thiols and flavinoids [4,5]. A number of assays have been developed for deter- mining the total radical-scavenging antioxidant capac- ity of biological fluids, which may be preferable to measures of specific antioxidant concentrations or activities. Global antioxidant measurements may be more physiologically relevant because they take ac- count of potential synergistic interactions between 0009-8981/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.cccn.2003.07.013 * Corresponding author. Tel.: +44-131-5372006; fax: +44-870- 1269869. E-mail address: s.waring@ed.ac.uk (W.S. Waring). www.elsevier.com/locate/clinchim Clinica Chimica Acta 338 (2003) 67 – 71