Dose‐response relations between urinary cadmium and tubular proteinuria in cadmium‐exposed workers

Cadmium in urine reflects the body burden in cadmium‐exposed individuals. Urinary β2‐microglobulin is frequently used as a marker of tubular proteinuria with an arbitrarily chosen value (34 μg/mmole creatinine) as the cut‐off limit. Both this cut‐off level and a lower limit (25 μg/mmole creatinine) were used in a study of the relationship between urinary cadmium and β 2 ‐microglobulin in 561 cadmium‐exposed battery workers. There was a clear dose‐response relation between the urinary cadmium level and the prevalence of tubular proteinuria ranging from 0.8% in the lowest exposure group, excreting less than 1 nmole cadmium/mmole creatinine, to 46.4% (50.0 for the lower cut‐off level) in the highest exposure group with a mean urinary cadmium of 15 nmole/mmole creatinine. The relation between urinary cadmium and tubular proteinuria was also assessed using probit analysis. There was a 10% response at a urinary cadmium of 3 nmole/mmole creatinine. The impact of age on the dose‐response relation was explored in two age groups with the cut‐off point at 60 years of age, showing a 10% prevalence of tubular proteinuria at urinary cadmium levels of 1.5 nmole/mmole creatinine in this older age group and 5.0 nmole/mmole creatinine in the category under 60 years of age. The study thus indicates that the present health‐based limit (10 nmole/mmole creatinine) proposed by the World Health Organization (WHO) is too high and it is suggested that a new limit should be set to 3 nmole/mmole creatinine.