title: Human and methodological sources of variability in the measurement of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine.
abstract: OBJECTIVE
  Urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is a widely used biomarker of oxidative stress. However, variability between chromatographic and ELISA methods hampers interpretation of data, and this variability may increase should urine composition differ between individuals, leading to assay interference. Furthermore, optimal urine sampling conditions are not well defined. We performed inter-laboratory comparisons of 8-oxodG measurement between mass spectrometric-, electrochemical- and ELISA-based methods, using common within-technique calibrants to analyze 8-oxodG-spiked phosphate-buffered saline and urine samples. We also investigated human subject- and sample collection-related variables, as potential sources of variability.
  
  
  RESULTS
  Chromatographic assays showed high agreement across urines from different subjects, whereas ELISAs showed far more inter-laboratory variation and generally overestimated levels, compared to the chromatographic assays. Excretion rates in timed 'spot' samples showed strong correlations with 24 h excretion (the 'gold' standard) of urinary 8-oxodG (rp 0.67-0.90), although the associations were weaker for 8-oxodG adjusted for creatinine or specific gravity (SG). The within-individual excretion of 8-oxodG varied only moderately between days (CV 17% for 24 h excretion and 20% for first void, creatinine-corrected samples).
  
  
  METHODS
  This is the first comprehensive study of both human and methodological factors influencing 8-oxodG measurement, providing key information for future studies with this important biomarker.
  
  
  CONCLUSIONS
  ELISA variability is greater than chromatographic assay variability, and cannot determine absolute levels of 8-oxodG. Use of standardized calibrants greatly improves intra-technique agreement and, for the chromatographic assays, importantly allows integration of results for pooled analyses. If 24 h samples are not feasible, creatinine- or SG-adjusted first morning samples are recommended.
authors.affiliation: Department of Occupational and Environmental Medicine, University of Gothenburg, Gothenburg, Sweden. lars.barregard@amm.gu.se
authors.forename: Lars
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authors.lastname: Barregard
authors.forename: Peter
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authors.initials: MD
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authors.forename: Yun-Shan
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authors.lastname: Sakai
authors.forename: Rajinder
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authors.forename: Friederike
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authors.forename: Rafal
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authors.lastname: Rozalski
authors.forename: Daniel
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authors.lastname: Gackowski
authors.forename: Agnieszka
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authors.lastname: Siomek
authors.forename: Guillermo T
authors.initials: GT
authors.lastname: Saez
authors.forename: Concha
authors.initials: C
authors.lastname: Cerda
authors.forename: Karin
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authors.lastname: Broberg
authors.forename: Christian
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authors.lastname: Lindh
authors.forename: Mohammad Bakhtiar
authors.initials: MB
authors.lastname: Hossain
authors.forename: Siamak
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authors.lastname: Haghdoost
authors.forename: Chiung-Wen
authors.initials: CW
authors.lastname: Hu
authors.forename: Mu-Rong
authors.initials: MR
authors.lastname: Chao
authors.forename: Kuen-Yuh
authors.initials: KY
authors.lastname: Wu
authors.forename: Hilmi
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authors.lastname: Orhan
authors.forename: Nilufer
authors.initials: N
authors.lastname: Senduran
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Smith
authors.forename: Regina M
authors.initials: RM
authors.lastname: Santella
authors.forename: Yali
authors.initials: Y
authors.lastname: Su
authors.forename: Czarina
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authors.lastname: Cortez
authors.forename: Susan
authors.initials: S
authors.lastname: Yeh
authors.forename: Ryszard
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authors.lastname: Olinski
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authors.lastname: Loft
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authors.initials: MS
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mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D000328:Adult; D016477:Artifacts; D002021:Buffers; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000032:analysis / Q000652:urine; D005260:Female; D006258:Head and Neck Neoplasms / Q000652:urine; D006801:Humans; D008297:Male; D008875:Middle Aged; D012015:Reference Standards; D015203:Reproducibility of Results; D012965:Sodium Chloride; D012996:Solutions; D016482:Urinalysis / Q000592:standards*; D055815:Young Adult
chemical_list: D002021:Buffers; D012996:Solutions; D012965:Sodium Chloride; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine