Urinary cadmium and some urinary indicators of kidney tubular damage in a population exposed to chronic environmental ca
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LETTER TO THE EDITOR
Urinary cadmium and some urinary indicators of kidney tubular damage in a population exposed to chronic environmental cadmium Tomoyuki Kawada1 Received: 25 February 2020 / Accepted: 6 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Keywords Urinary cadmium · Kidney tubular damage · Cadmium · Chronic exposure · Risk assessment Eom et al. (2020) conducted a cross-sectional study in general inhabitants exposed to environmental cadmium (Cd). Kidney tubular damage was assessed by urinary beta-2 microglobulin (BMG), N-acetyl-β- d -glucosaminidase (NAG) activity and malondialdehyde (MDA) levels. The serum copper-to-zinc ratio (CZR) was used as an essential metal imbalance indicator. The authors clarified that serum CZR had an influence on the relationship between urinary cadmium level and kidney tubular damage. By multiple regression analysis, it was revealed that serum CZR was significantly associated with urinary BMG levels in the low Cd exposure group and was significantly associated with urinary MDA levels, regardless of Cd exposure level. In addition, urinary Cd was significantly associated with urinary NAG and BMG levels in the high Cd exposure group. I have some concerns on their study. The authors used multiple regression analysis to investigate the association between urinary Cd, serum CZR and urinary markers of kidney tubular damage. Dependent variables and independent urinary CD were not adjusted by urinary creatinine. Although the authors used urinary creatinine for the adjustment of multivariate analysis, urinary creatinine should be used for concentrations of urinary Cd and urinary markers of kidney tubular damage of the spot urine. I recommend the authors to use urinary creatinine before applying to statistical model. Second, the authors used 2 µg/g creatinine as a cut-off point of low and high cadmium exposure. According to the criteria, multiple regression analysis was also conducted. But sex ratio differed between two groups, which might contribute to the difference of smoking habit. This means that * Tomoyuki Kawada [email protected] 1
two groups present different characteristics of comorbidities, which would be related to kidney dysfunction. In combination with subgroup analysis, multivariate analysis by total data should also be presented. Third, the same authors previously conducted a crosssectional study in inhabitants, who had not been exposed to occupational Cd exposure (Eom et al. 2017). The geometric mean concentration of Cd in urine was around 1 µg/g creatinine). Urinary Cd was significantly correlated with urinary BMG and NAG activity after controlling for various confounding variables. In addition, urinary MDA was associated with urinary Cd level in a dose-dependent manner. Regarding this result, I previously reported that urinary Cd was more closely associated with urinary NAG than with BMG in Cd-exposed male workers, whose geometric mean value of urinary Cd level was around 1 µg/g creatinine (Kawada et al. 1990). Increased urinary markers m
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