engleski

Temporal stability of a reference material for erythrocyte superoxide dismutase (Cu, Zn-SOD) determination

Determination of erythrocyte superoxide dismutase (Cu, Zn-SOD) activity is used for evaluation of antioxidant status, and may be used for indirect assessment of copper status in an individual. Standardization in enzymology requires not only a reference method but also a reference material in order to ensure accuracy of the enzyme analysis and to enable comparison of results on the international level. We used the European Community - FLAIR common method for Cu, Zn-SOD determination (Belsten & Wright, Eur J Clin Nutr 1995 ; 49:928-931) and the Ransod Control lyophilized bovine whole blood (Cat. No. SD 126, Randox Laboratories Ltd, UK) as a reference sample. The study evaluated the temporal stability of this reference material following its reconstitution with deionized water and storage at 4 oC for up to 25 days. Two different samples of the Ransod Control (Lot 170RD and Lot 183RD) were reconstituted simultaneously and analyzed in quadriplicates on the same day (Day 0), and following 1, 2, 3, 5, 7, 10, 14, 19, and 25 days. On each day of the analyses a calibration line was prepared by using the Ransod Standard. The relative standard deviation (RSD) concerning repeatability (the within-day RSD) was in the range of 1.5-3.5% and 1.5-3.2% for lots 170RD and 183RD, respectively. The results for both lots showed a weak linear decline of the mean Cu, Zn-SOD values in the period of 25 days. According to linear regression, the decrease in Cu, Zn-SOD values between Day 0 and Day 25 was 8.0% and 7.9% for lots 170RD and 183RD, respectively. However, although the samples of both lots were analyzed simultaneously and the same calibration line was used, our results fitted in the reference range for one lot but were somewhat higher for the other lot ; the overall results (mean ± standard deviation) for Lot 183RD were 325 ± 10 U/ml as compared to the reference range 300 +/- 54 U/ml, whereas those for Lot 170RD were 298 ± 9 U/ml as compared to the reference range 250 +/- 45 U/ml. Nevertheless, the reference range (i.e., the declared approximate concentration) of Cu, Zn-SOD in the Ransod Control appears to be overly wide, which makes this reference material poorly applicable for research purposes.

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