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Blood lead-urine lead relationships in adults and children
B L Gulson1, M A Cameron, A J Smith
1Graduate of School of the Environment, Macquire University, Sydney, New South Wales, Australia.
Insights
Urine lead isotope ratios can indicate blood lead exposure, but urine lead concentrations do not reliably predict blood lead levels, especially at low exposures. This finding is crucial for monitoring lead exposure in infants and adults.
Area of Science:
- Environmental Health
- Toxicology
- Analytical Chemistry
Background:
- Blood lead concentration is the standard biomarker for lead exposure.
- Non-invasive or less invasive biomarkers are needed for frequent monitoring, especially in vulnerable populations like infants.
- Urine analysis offers a potential alternative, but its reliability for lead exposure assessment requires validation.
Purpose of the Study:
- To evaluate the utility of urine as a surrogate for blood in lead exposure assessment.
- To compare lead concentrations and isotopic measurements in paired blood and urine samples.
- To determine if urine lead isotopic ratios can serve as a proxy for blood lead isotopic ratios.
Main Methods:
- Collected paired venous blood and spot urine samples from over 260 subjects.
- Performed high-precision lead isotopic measurements on all samples.
- Analyzed lead concentrations in both blood and urine.
- Monitored an adult male over 24 months with weekly urine and monthly blood samples.
- Compared spot urine samples with 24-hour urine samples for two subjects.
Main Results:
- High correlation observed between blood and urine lead isotope ratios, suggesting urine can be a proxy for blood isotopic measurements.
- Approximately 10% of measurements showed significant discrepancies between blood and urine, often attributed to urine sample contamination.
- Lead concentrations in blood and urine showed only a weak relationship, with urine concentrations unable to predict blood concentrations, particularly at low exposure levels (<10 microgram/dL).
- Weekly urine and monthly blood monitoring showed excellent correlations over 24 months, despite higher standard deviations in urine.
- Spot urine analyses agreed well with 24-hour urine samples.
Conclusions:
- Lead isotopic measurements in urine are a viable proxy for blood isotopic measurements, useful for tracking lead sources and body burden dynamics.
- Lead concentrations in urine are not a reliable indicator of blood lead concentrations, limiting its use for quantitative exposure assessment.
- Careful sample collection protocols are essential to prevent contamination during urine lead analysis.
Abstract:
To determine the potential for using instead of blood as an indicator of lead exposure, especially in infants, lead concentrations and high-precision lead isotopic measurements have been compared in venous blood and "spot" urine (n > 260 from 182 different subjects) collected within the same 24-h period. Physiological conditions for the children and most of the adults were considered to be in a steady-state between body stores and lead in the environment. In the case of some adults, conditions were initially not steady-state because exposure conditions changed (for example, subjects moved to a country with lead of different isotopic composition.) There was a high correlation (r2 = ) between the blood and urine measurements of the isotope ratios but about 10% of measurements were outliers--the blood and urine measurements were further apart than was consistent with the measurement error that was generally obtained. The discrepancy was usually found to be associated with the urine measurement and was attributed to contamination during sampling. Weekly urine and monthly blood monitoring of an adult male over a 24-month period showed and excellent correlations, although the standard deviations were about an order of magnitude higher than the precision measured for replicate analyses of a single blood or urine sample. "Spot" urine analyses for two male subjects gave excellent agreement with 24-h urine samples. Standard deviations of the spot analyses were of similar order to those in the 24-month monitored subject. In cases where female adults from Eastern Europe migrated to Australia, there was generally a more rapid exchange of skeletal lead with Australian environmental lead in urine compared with blood. These data do not support a differential partitioning of endogenous lead into the plasma. At this stage, isotopic measurements of urine can be used as a proxy for isotopic measurements in blood. However, lead concentrations in blood and in urine are only weakly related. Concentrations of lead in urine cannot serve to predict concentrations of lead in blood, particularly at the lower range of exposures, for example, at blood concentrations less than 10 microgram/d1.