Application of path analysis to urinary findings of cadmium-induced renal dysfunction

In order to identify some causal relations among various urinary indices of cadmium-induced renal dysfunction, such as glucose, total protein, amino nitrogen, Bz-microglobulin (beta (2)-m), metallothionein (MT), and cadmium (Cd), we applied path analysis method to previous epidemiological studies targeting the residents of the Cd-polluted Kakehashi River basin of Ishikawa Prefecture, Japan. We obtained a diagram-termed path model, representing some causal relations among the above urinary indices. It shows that urinary Cd is located at the beginning point in the diagram, and Cd-induced renal dysfunction develops in the following order: Cd exposure --> increase of beta (2)-m and/or MT excretion --> increase of amino-N and/or total protein excretion --> increase of glucose excretion. It was proved mathematically, that in the case of both males and females, increased excretions of beta (2)-m and/or MT were the most sensitive urinary indices of the early stage of chronic Cd-induced renal dysfunction.