title: Assaying organochlorines in archived serum for a large, long-term cohort: implications of combining assay results from multiple laboratories over time.
abstract: Conserving irreplaceable, archived serum samples may sometimes conflict with the objective of minimizing measurement error due to laboratory effects. We sought to determine whether we could successfully combine assay results for DDT-related compounds and polychlorinated biphenyls (PCBs) in serum from the same birth cohort obtained from different laboratories over time. Using the Child Health and Development Studies (CHDS) serum archive, we compared variability for assays of a quality control pool to variability for assays of subject serum. The quality control pool was created from native archived serum samples that were pooled, then aliquoted, blinded and inserted pair-wise into assay batches along with the subject serum for 5 studies using CHDS samples conducted over a 13year period by three different laboratories. We found that the variability between laboratory and over time within laboratory was small relative to inter-individual variability for p,p'-DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), p,p'-DDE (1,1'-dichloro-2,2'-bis(p-chlorophenyl)ethylene) and o,p'-DDT (1,1,1-trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)-ethane). Results were also consistent for most PCB congeners which were detectable in 85% or more of samples. Our results suggest that it is possible to combine assays for DDT and PCB congeners measured at positive levels as they are accumulated for cohort subjects without risking meaningful misclassification due to variation stemming from laboratory or time period. This has significant implications for future study costs, conservation of irreplaceable archived samples and for leveraging past investments for future research. For PCB congeners with very low levels, findings caution against pooling of assays without further exploration.
authors.affiliation: Child Health and Development Studies, Public Health Institute, Berkeley, CA 94709, USA.
authors.forename: Robert I
authors.initials: RI
authors.lastname: Sholtz
authors.forename: Katherine R
authors.initials: KR
authors.lastname: McLaughlin
authors.forename: Piera M
authors.initials: PM
authors.lastname: Cirillo
authors.forename: Myrto
authors.initials: M
authors.lastname: Petreas
authors.forename: June-Soo
authors.initials: JS
authors.lastname: Park
authors.forename: Mary S
authors.initials: MS
authors.lastname: Wolff
authors.forename: Pam
authors.initials: P
authors.lastname: Factor-Litvak
authors.forename: Brenda
authors.initials: B
authors.lastname: Eskenazi
authors.forename: Nickilou
authors.initials: N
authors.lastname: Krigbaum
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Cohn
mesh_terms: D001681:Biological Assay / Q000379:methods*; D001774:Blood Chemical Analysis / Q000379:methods*; D015331:Cohort Studies; D003634:DDT / Q000097:blood*; D004785:Environmental Pollutants / Q000097:blood*; D005260:Female; D006801:Humans; D007753:Laboratories; D018811:Maternal Exposure / Q000706:statistics & numerical data; D011078:Polychlorinated Biphenyls / Q000097:blood*; D011247:Pregnancy; D011786:Quality Control
chemical_list: D004785:Environmental Pollutants; D003634:DDT; D011078:Polychlorinated Biphenyls