Urinary metallothionein as a new index of renal dysfunction in "Itai-Itai" disease patients and other Japanese women environmentally exposed to cadmium.

The significance of elevated excretion of metallothionein in urine of women living in cadmium-polluted areas of Japan was studied with respect to renal dysfunction. The relationships between the concentrations of metallothionein in urine and those of other non-specific urinary indices of renal dysfunction, i.e., total protein, glucose, beta 2-microglobulin, retinol-binding protein, alpha-amino nitrogen and proline were examined. In addition, the relationships between urinary metallothionein and urinary cadmium and copper were also evaluated. It was found that the logarithm of the metallothionein concentration in urine was significantly correlated with the logarithm of the concentrations of each of the above parameters. When subjects with signs of renal dysfunction, including "itai'itai" disease patients and patients suspected of the disease, were compared with subjects with normal renal functions, as a group, the former excreted significantly higher concentrations of metallothionein in their urine than the latter. The results suggest that the elevated excretion of metallothionein is not only an index of excessive cadmium exposure, but also of renal dysfunction caused by chronic exposure to this metal.