Reversibility of microproteinuria in nickel-cadmium battery workers after removal from exposure

Objectives: The study was aimed at assessing the reversibility of renal tubule dysfunction in workers exposed to cadmium according to the severity of microproteinuria, concentrations of cadmium in urine (Cd-U), and the time since removal from exposure. Methods: The study was carried out in a nickel-cadmium battery factory. Exposure to cadmium was formerly very high. In 1983 and in 1986-1988, geometric mean concentrations of cadmium in blood (Cd-B) of workers amounted to 23.3 mug/l and 55.7 mug/l, respectively. Workers with determinations of Cd-B, Cd-U and retinol binding protein in urine (RBP-U) in the past were eligible for the study. Fifty-eight workers who had met this profile and had been removed from exposure to cadmium before 1998 were investigated in 1998-1999. They were divided into three groups according to their RBP-U concentrations in 1986-1988: <300 (n=26); 301-1,501 (n=25) and >1,501 mug/g creatinine (n=7). Results: In 1999, the RPB-U levels were below 300 mug/g creatinine in 85%, 64% and 42% of persons from groups 1, 2 and 3, respectively. Statistical analysis of the results by means of multi-parametric logistic regression analysis revealed that, from the viewpoint of reversibility of tubular proteinuria, its severity in 1986-1988 was most important. Also. the time since the removal from exposure to cadmium and Cd-U levels seemed to play some role, but the influence of these parameters was not statistically significant. Significant correlation between beta(2)-microglobulin in serum (beta(2)M-S) and RBP-U concentrations measured in 1998-1999 with apparent lack of correlation between beta(2)M-S and RBP-U concentrations in 1986-1988 supports the hypothesis that the glomerular impairment induced by cadmium may be secondary to the tubular lesion rather than independent from tubular effect. Conclusions: The results show that the tubular proteinuria, and maybe also the decline in glomerular filtration rate, may be reversible, even in the case of relatively high past exposure. The results confirm the necessity for monitoring urinary levels of low-molecular-weight proteins during periodic examination of workers exposed to cadmium.