Spot urinary concentrations of environmental exposure biomarkers require correction for dilution. There is no consensus on the most appropriate method, with creatinine used by default despite lacking theoretical robustness. We comparatively assessed the efficacy of creatinine; specific gravity (SG); osmolality and modifications of all three for dilution correcting urinary arsenic. For 202 participants with urinary arsenic, creatinine, osmolality and SG measurements paired to drinking water As, we compared the performance corrections against two independent criteria: primarily, (A) correlations of corrected urinary As and the dilution measurements used to correct them - weak correlations indicating good performance and (B) correlations of corrected urinary As and drinking water As - strong correlations indicating good performance. More than a third of variation in spot urinary As concentrations was attributable to dilution. Conventional SG and osmolality correction removed significant dilution variation from As concentrations, whereas conventional creatinine over-corrected, and modifications of all three removed measurable dilution variation. Modified creatinine and both methods of SG and osmolality generated stronger correlations of urinary and drinking water As concentrations than conventional creatinine, which gave weaker correlations than uncorrected values. A disparity in optima between performance criteria was observed, with much smaller improvements possible for Criterion B relative to A. Conventional corrections – particularly creatinine - limit the utility spot urine samples, whereas a modified technique outlined here may allow substantial improvement and can be readily retrospectively applied to existing datasets. More studies are needed to optimize urinary dilution correction methods. Covariates of urinary dilution measurements still warrant consideration.
Bibliographical noteFunding Information:
We thank Elliott Hamilton, Louise Ander, Andrew Marriott and Andrew Dunne (BGS) and Tony Fletcher, Giovanni Leonardi, Rebecca Close, Helen Crabbe, Karen Exley, Amy Rimell and Mike Studden (PHE) for their involvement in the wider Cornwall arsenic biomonitoring project. We thank Nigel Kendall and David Gardner from the University of Nottingham Biosciences for facilitating creatinine and osmolality measurements. Murray Lark, Chris Milne, Mark Cave and Simon Chenery from the BGS are thanked for advice. The time and contributions of the study participants are gratefully acknowledged. This work was undertaken during a NERC-funded University of Manchester/BUFI (Centre for Environmental Geochemistry) PhD studentship (GA/125/017, BUFI Ref: S204.2) and completed during a Postdoctoral Fellowship at the International agency for Research on Cancer (IARC), partially supported by the European Commission FP7 Marie Curie Actions – People – Co-funding of regional, national and international programmes (COFUND). None.
This work was undertaken during a NERC-funded University of Manchester / BUFI (Centre for Environmental Geochemistry) PhD studentship ( GA/125/017 , BUFI Ref: S204.2 ) and completed during a Postdoctoral Fellowship at the International agency for Research on Cancer (IARC), partially supported by the European Commission FP7 Marie Curie Actions – People – Co-funding of regional, national and international programmes (COFUND).
- Hydration correction
ASJC Scopus subject areas
- Environmental Science(all)