Meta-analysis for deriving age- and gender-specific dose–response relationships between urinary cadmium concentration and β2-microglobulinuria under environmental exposure

A meta-analysis was conducted to derive age- and gender-specific dose–response relationships between urinary cadmium (Cd) concentration and β2-microglobulinuria (β2MG-uria) under environmental exposure. β2MG-uria was defined by a cutoff point of 1000 μg β2-microglobulin/g creatinine. We proposed a model for describing the relationships among the interindividual variabilities in urinary Cd concentration, the ratio of Cd concentrations in the target organ and in urine, and the threshold Cd concentration in the target organ. The parameters in the model were determined so that good agreement might be achieved between the prevalence rates of β2MG-uria reported in the literature and those estimated by the model. In this analysis, only the data from the literature on populations environmentally exposed to Cd were used. Using the model and estimated parameters, the prevalence rate of β2MG-uria can be estimated for an age- and gender-specific subpopulation for which the distribution of urinary Cd concentrations is known. The maximum permissible level of urinary Cd concentration was defined as the maximum geometric mean of the urinary Cd concentration in an age- and gender-specific subpopulation that would not result in a statistically significant increase in the prevalence rate of β2MG-uria. This was estimated to be approximately 3 μg/g creatinine for a population in a small geographical area and approximately 2 μg/g creatinine for a nationwide population.