An  assessment of sensitivity biomarkers for urinary cadmium burden

Background: Excess cadmium (Cd) intake poses a general risk to health and to the kidneys in particular. Among indices of renal dysfunction under Cd burden measures are the urinary N-acetyl-β-D-glucosidase (UNAG) and urinary β 2 -microglobulin (Uβ 2 -MG) enzymes. However, the end-pointed values and the Cd burden threshold remain controversial because the scopes fluctuate widely. Methods: : To ascertain the clinical benchmark dose of urinary Cd (UCd) burden for renal dysfunction, 1595 residents near a Cd site were surveyed. Urine was sampled and assayed. A benchmark dose low (BMDL) was obtained by fitting UCd levels and index levels. Results: : We found that over 50% of the subjects were suffering from Cd exposure as their UCd levels far exceeded the national standard threshold of 5.000 μg/g creatinine (cr). Further analysis indicated that Uβ 2 -MG was more sensitive than UNAG for renal dysfunction. The BMDL for UCd was estimated as 3.486 U/g cr (male, where U is unit of enzyme) and 2.998 U/g cr (female) for UNAG. The BMDL for Uβ 2 -MG, which is released into urine from glomerulus after Cd exposure, was found to be 2.506 μg/g cr (male, where μg is the unit of microglobulin) and 2.236 μg/g cr (female). Conclusions: : Uβ 2 -MG is recommended as the sensitivity index for renal dysfunction, with 2.2 μg/g cr as the threshold for clinical diagnosis. Our findings suggest that Uβ 2 -MG is the better biomarker for exposure to Cd.