Temperature stability of urinary F2-isoprostane and 8-hydroxy-2-deoxyguanosine

Background: Clinical and epidemiological studies employ long -term temperature storage but the effect of temperature on the stability of oxidative stress (OS) markers is unknown. We investigated the effects of storage at -20 degrees C and -80 degrees C over 4-9 months on F-2-isoprostanes (F-2-IsoP) and 8-hydroxy-2 '-deoxyguanosine (8-OHdG) levels in urine of children, a population group among whom the measurement of these markers is still limited. Methods: Paired spot urine samples from 87 children aged 8.9-16.9 years (52.9% boys) were analyzed. Samples were preserved with 0.005% (w/v) butylated hydroxytoluene, portioned and stored within 2.5 h (median) of collection. Samples were analyzed in duplicate or triplicate using commercial ELISA kits and their correlations were evaluated. Results: F-2-IsoP and 8-OHdG showed high correlations (Spearman rho of 0.90 and 0.97, respectively; P < 0.0001) with storage at -20 degrees C and -80 degrees C. There was a strong agreement among categories of values for F-2-IsoP (Kappa = 0.76 +/- 0.08, agreement = 83.9%, P < 0.0001) and 8OHdG: (Kappa = 0.83 +/- 0.08, agreement = 88.4%, P < 0.0001). The correlation between the temperatures for F-2-IsoP concentrations was also high when stored for <4 (0.93), 4 (0.93), and 5 months (0.88), all P < 0.0001. For 8-OHdG, Spearman correlations at <8, 8, and 9 months of storage at -20 degrees C and -80 degrees C were 0.95, 0.98, and 0.96 (all P < 0.0001), respectively. Conclusions: Urine storage with BHT for up to nine months at a temperature of -20 degrees C to -80 degrees C yields highly comparable concentrations of F-2-IsoP and 8-OHdG.