REDUCED ALIQUOT SIZE FOR A PLASMA ORGANOCHLORINE ASSAY FOR USE IN EPIDEMIOLOGIC STUDIES

Because archived blood specimens are an important but limited resource for conducting epidemiological studies using biomarkers, it is import ant to develop analytical techniques that minimize the amount of sampl e needed, We modified an established 1.0-ml blood plasma organochlorin e assay to use smaller volumes, We assessed its utility by comparing t he accuracy and precision of measurements obtained with different-size d aliquots of spiked plasma from three pools of known concentration of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) and polychlorinate d biphenyls (PCBs; low, medium, and high), There was a modest sacrific e in accuracy using 0.5 as opposed to 1.0 mi, However, the within-batc h coefficients of variation, a measure of laboratory error, were consi stently low when 0.5-ml aliquots were used. For both DDE and PCB conce ntrations, this error was less than 5% for the medium and high pools [ 5-20 parts per billion (ng/ml)] and less than 9% for the low pool (<1 part per billion), After determining that aliquots of 0.5 mi were suff icient, we performed a blinded quality control analysis of stored plas ma, In this study, the within-subject variation was low for DDE and PC Bs and substantially lower than the between-subject variation, suggest ing that the assay would rank subjects with reasonable precision, Our results suggest that use of 0.5-ml as opposed to 1.0-ml aliquots shoul d not compromise the po,ver of a nested case-control study to detect d ifferences between subjects and would thus save plasma for future rese arch, For populations with very low levels of organochlorines, however , the larger volumes should still be used.