GLOMERULAR FUNCTION OF LEAD-EXPOSED WORKERS

Among lead-exposed workers, there is evidence of increased mortality from chronic renal diseases (nephritis and nephrosis). Epidemiological studies using early markers of nephropathy among lead-exposed workers failed to demonstrate early renal changes. This study is aimed at assessing the glomerular function of 137 lead-exposed subjects and at evaluating whether changes in markers of glomerular function are related to exposure indices derived from longitudinal blood lead data. A control group of 153 postal workers was also investigated. Several exposure indices were derived for the exposed workers, including a time-integrated index Pb in blood (PbB)(int) and the number of times the PbB was above critical values (PbB400, PbB500, PbB600). Through multiple linear regression analysis, PbBint was the best predictor of variation in serum beta(2)-microglobulin (S beta(2)m) and alpha(1)-microglobulin (S alpha(1)m) and urinary albumin (UAlb). A small but statistically significant difference in the mean beta(2)m was found. S beta(2)m was also the only marker showing a significantly higher prevalence rate ratio (PRR) of abnormalities among lead-exposed workers. Though there was no clear dose-response relationship with PbBint as the index of dose, all the 15 subjects with abnormal S beta(2)m in the older age group were found in the highest PbBint group. Furthermore, of the 8 subjects with low 4-h creatinine clearance (CrCl4h), 6 had abnormal levels of beta(2)m. Two subjects with CrCl4h, of less than 75 ml/min/1.74 m(2) had high PbBint values, thus suggesting that high blood lead levels over a prolonged time may be associated with decreased CrCl4h. Though the long-term significance of elevated S beta(2)m and UAlb is unclear, their association with high PbBint and decreasing CrCl4h indicate a potentially adverse effect. Their relationship with PbB400 and PbB600 suggests that the threshold of 700 mu g/l for PbB may not prevent the occurrence of lead nephropathy.