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Urinary creatinine adjustment for uranium and kidney outcomes from lead workers

Journal of Exposure Science & Environmental Epidemiology volume 25, pages 119–120 (2015)Cite this article

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Shelley et al.1 reported that urinary adjustment by creatinine in nephrotoxic research had an effect on the association between uranium and kidney outcomes in lead workers. They used urinary N-acetyl-beta-d-glucosaminidase (NAG), two types of estimated glomerular filtration rate (eGFR), or measured creatinine clearance as a dependent variable, and urinary uranium was used as an independent variable in combination with several associated factors for multiple regression analysis. Urinary uranium was measured from spot urine, by creatinine adjustment and from 4-hour urine collection. The authors concluded that creatinine adjustment should be done cautiously to determine the net association between uranium exposure and kidney outcomes. I fundamentally agree with their statistical procedure, but I have some concerns on their result.

First, the authors handled the lead workers with a median value of blood lead of 21.5 mg/dl. In addition, the median value of urinary cadmium was 0.83 mg/g creatinine and the target subjects were assumed as population with low-level exposure to lead or cadmium. I previously reported that urinary NAG was also an early biological marker for renal effects,2 and the environmental exposure level was almost the same with Shelley’s population. Urinary uranium was associated with blood lead in their population, and I speculate that significant association between urinary uranium and urinary NAG after adjustment by several confounders is considered to be uranium association with kidney outcomes. NAG cannot pass through the glomerulus and urinary NAG is presented by a damage of renal proximal tubules. The same association was observed in measured creatinine clearance, and renal effect was supposed to be existed in both glomerulus and proximal tubules. As eGFR was derived from mathematical equation, and caution should be paid on its validity.3, 4

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References

  1. Shelley R, Kim NS, Parsons PJ, Lee BK, Agnew J, Jaar BG et al. Uranium associations with kidney outcomes vary by urine concentration adjustment method. J Expo Sci Environ Epidemiol 2014; 24: 58–64.

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  1. Department of Hygiene and Public Health, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo, Japan

    Tomoyuki Kawada

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  1. Tomoyuki Kawada
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Correspondence to Tomoyuki Kawada.

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Kawada, T. Urinary creatinine adjustment for uranium and kidney outcomes from lead workers. J Expo Sci Environ Epidemiol 25, 119–120 (2015). https://doi.org/10.1038/jes.2014.77

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