Assessing urinary flow rate, creatinine, osmolality and other hydration adjustment methods for urinary biomonitoring using NHANES arsenic, iodine, lead and cadmium data

Daniel R.S. Middleton, Michael J. Watts, R. Murray Lark, Chris J. Milne, David A. Polya*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

74 Citations (Scopus)
23 Downloads (Pure)


Background: There are numerous methods for adjusting measured concentrations of urinary biomarkers for hydration variation. Few studies use objective criteria to quantify the relative performance of these methods. Our aim was to compare the performance of existing methods for adjusting urinary biomarkers for hydration variation. 

Methods: Creatinine, osmolality, excretion rate (ER), bodyweight adjusted ER (ERBW) and empirical analyte-specific urinary flow rate (UFR) adjustment methods on spot urinary concentrations of lead (Pb), cadmium (Cd), non-arsenobetaine arsenic (AsIMM) and iodine (I) from the US National Health and Nutrition Examination Survey (NHANES) (2009-2010 and 2011-2012) were evaluated. The data were divided into a training dataset (n = 1,723) from which empirical adjustment coefficients were derived and a testing dataset (n = 428) on which quantification of the performance of the adjustment methods was done by calculating, primarily, the correlation of the adjusted parameter with UFR, with lower correlations indicating better performance and, secondarily, the correlation of the adjusted parameters with blood analyte concentrations (Pb and Cd), with higher correlations indicating better performance. 

Results: Overall performance across analytes was better for Osmolality and UFR based methods. Excretion rate and ERBW consistently performed worse, often no better than unadjusted concentrations. 

Conclusions: Osmolality adjustment of urinary biomonitoring data provides for more robust adjustment than either creatinine based or ER or ERBW methods, the latter two of which tend to overcompensate for UFR. Modified UFR methods perform significantly better than all but osmolality in removing hydration variation, but depend on the accuracy of UFR calculations. Hydration adjustment performance is analyte-specific and further research is needed to establish a robust and consistent framework.

Original languageEnglish
Article number68
JournalEnvironmental Health: A Global Access Science Source
Publication statusPublished - 10 Jun 2016
Externally publishedYes

Bibliographical note

Funding Information:
Funding was provided by the Natural Environment Research Council (NERC) via a University of Manchester/BUFI (Centre for Environmental Geochemistry) studentship (Contract No. GA/125/017, BUFI Ref: S204.2).

Publisher Copyright:
© 2016 The Author(s).


  • Biomonitoring
  • Creatinine
  • Hydration adjustment
  • Osmolality
  • Urinary flow rate

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Health, Toxicology and Mutagenesis


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