The Utility of Spot vs 24-Hour Urine Samples for Metal Determination in Veterans With Retained Fragments

Objectives: The objective of this investigation is to explore the utility of using a spot urine sample in lieu of a 24-hour collection in assessing fragment-related metal exposure in war-injured veterans.

Methods: Twenty-four veterans collected each urine void over a 24-hour period in separate containers. Concentrations of 13 metals were measured in each void and in a pooled 24-hour sample using inductively coupled plasma mass spectrometry. To assess the reliability of spot sample measures over time, intraclass correlations (ICCs) were calculated across all spot samples. Lin's concordance correlation coefficient was used to assess agreement between a randomly selected spot urine sample and each corresponding 24-hour sample.

Results: In total, 149 spot urine samples were collected. Ten of the 13 metals measured had ICCs more than 0.4, suggesting "fair to good" reliability. Concordance coefficients were more than 0.4 for all metals, suggesting "moderate" agreement between spot and 24-hour concentrations, and more than 0.6 for seven of the 13 metals, suggesting "good" agreement.

Conclusions: Our fair to good reliability findings, for most metals investigated, and moderate to good agreement findings for all metals, across the range of concentrations observed here, suggest the utility of spot urine samples to obtain valid estimates of exposure in the longitudinal surveillance of metal-exposed populations.