Associations of low-level urine cadmium with kidney function in lead workers.

OBJECTIVES Low-level cadmium exposure, resulting in, for example, urinary cadmium <2.0 μg/g creatinine, is widespread; recent data suggest nephrotoxicity even at these low levels. Few studies have examined the impact of low-level cadmium exposure in workers who are occupationally exposed to other nephrotoxicants such as lead. METHODS We evaluated associations of urine cadmium, a measure of cumulative dose, with four glomerular filtration measures and N-acetyl-β-D-glucosaminidase (NAG) in lead workers. Recent and cumulative lead doses were assessed via blood and tibia lead, respectively. RESULTS In 712 lead workers, mean (SD) blood and tibia lead values, urine cadmium values and estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease equation were 23.1 (14.1) μg/dl, 26.6 (28.9) μg Pb/g bone mineral, 1.15 (0.66) μg/g creatinine and 97.4 (19.2) ml/min/1.73 m(2), respectively. After adjustment for age, sex, body mass index, urine creatinine, smoking, alcohol, education, annual income, diastolic blood pressure, current or former lead worker job status, new or returning study participant, and blood and tibia lead, higher ln-urine cadmium was associated with higher calculated creatinine clearance, eGFR (β = 8.7 ml/min/1.73 m(2); 95% CI 5.4 to 12.1) and ln-NAG but lower serum creatinine. CONCLUSIONS Potential explanations for these results include a normal physiological response in which urine cadmium levels reflect renal filtration, the impact of adjustment for urine dilution with creatinine in models of kidney outcomes, and cadmium-related hyperfiltration.