Agency for Toxic Substances and Disease Registry
Case Studies in Environmental Medicine (CSEM) 

Pediatric Environmental Health
Direct Biologic Indicators

A 24-hour urine collection is obtained from the child and tested. It reveals a total mercury level of 321 micrograms per gram (µg/g) creatinine. Urine specimens are collected from the parents and grandmother and tested. The test results are expressed as urine mercury per gram creatinine, and are as follows: father, 18 µg/g creatinine; mother, 12 µg/g creatinine; and grandmother, 37 µg/g creatinine.

The World Health Organization's upper limit of normal for adults is 50 µg/g creatinine (World Health Organization 1991). The upper limit of normal for unexposed adults is 20 micrograms per liter (µg/L); most unexposed individuals have levels <5 µg/L (ATSDR 1999). However, the respective levels for children have not yet been established. More than likely, however, the upper limits are lower than those for adults. Urine mercury levels might be reported in different units of measure (e.g., micrograms per gram creatinine and micrograms per liter). A number of issues must be considered when interpreting results in children. These issues are discussed in more detail in Appendix B.

Some pediatric experts would regard a urinary mercury level >50 µg/g creatinine as in the toxic range and blood mercury >7-10 µg/dL as elevated. More information on acceptable urine and blood mercury levels in children can be found in Paulson (2001). However, the diagnosis of mercury poisoning should never be based solely on the results of a blood or urine test-environmental history and physical findings must support the diagnosis.

Urine or blood measurements in both adults and children who have chronic mercury exposure might not correlate with signs and symptoms of mercury toxicity. This might be due to several factors, including the storage of mercury in a relatively unexchangeable tissue compartment (i.e., renal cortex) or clearance from past exposure after irreversible signs and symptoms are manifested.

Further information on elemental mercury direct biologic indicators and treatment is in Appendix B.

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