Temporal changes in urinary levels of cadmium, N-acetyl-β-d-glucosaminidase and β2-microglobulin in individuals in a cadmium-contaminated area

• Urinary Cd levels decreased over time in individuals whose urinary Cd >2 μg/g creatinine.
• NAG activity decreased, but urinary β2-MG levels did not in those individuals.
• High urinary β2-MG levels in individuals who have exposed to Cd suggest the possibility of Cd-induced renal tubular damage.

Cadmium (Cd) is a metal that is toxic to renal tubules. If renal tubules are damaged by Cd, urinary excretion of N-acetyl-β-D-glucosaminidase (NAG) and beta 2-microglobulin (β2-MG) increases. The aim of this study was to describe the changing patterns of urinary Cd, NAG, and β2-MG levels over a 3-year period in individuals living in a Cd-contaminated area. This follow-up study included 191 residents (65.6 ± 9.3 years) who were living in the vicinity of a copper refinery. Urinary levels of Cd, NAG activity, and β2-MG levels were measured, and their determinants and changing patterns were analyzed statistically. The natural logarithm of urinary Cd levels decreased significantly over time. Sex and intake of locally cultivated rice were significant determinants of urinary Cd concentration. Urinary NAG activity decreased over time. Age and urinary Cd concentration were significant determinants of urinary NAG activity in subjects with urinary Cd concentrations >5 μg/g creatinine. In subjects whose urinary Cd concentrations were >2 μg/g creatinine, diabetes was found to be a significant risk factor for high urinary NAG activity. The slope for temporal changes in urinary β2-MG levels was negative in subjects whose urinary Cd levels were <2 μg/g creatinine but was positive in those whose urinary Cd levels were 2–5 μg/g creatinine or >5 μg/g creatinine. The urinary β2-MG levels found in individuals whose urinary Cd levels were >2 μg/g creatinine suggest that previous Cd-induced renal tubular damage had occurred.