Slotnick Melissa J, Meliker Jaymie R, Nriagu Jerome O
Department of Environmental Health Sciences, School of Public Health, The University of Michigan, Ann Arbor, Michigan 48109, USA.
J Expo Sci Environ Epidemiol. 2008 Mar;18(2):149-57. doi: 10.1038/sj.jes.7500569. Epub 2007 Apr 11.
Arsenic concentration in toenail clippings is used as a biomarker of exposure in epidemiological studies, often under the assumption that a single measurement represents long-term exposure. For this assumption to hold, the measured arsenic concentrations must be stable over time, yet temporal variability has not been adequately assessed. This study aims to evaluate temporal variability in multiple toenail samples collected from a population exposed to drinking water arsenic levels <100 microg/l. Our objectives are to investigate factors responsible for biomarker variability and to assess the suitability of single versus multiple measurements for determining exposure in epidemiological studies. Multiple toenail and drinking water samples were collected from 254 participants enrolled in a case-control study of arsenic exposure and bladder cancer in Michigan, USA; participants also answered questions on water consumption. Toenail samples collected an average of 14 months apart were positively correlated, although a substantial amount of variability was detected (r=0.43, P<0.0001, n=236). Arsenic concentration in drinking water was stable and small changes in drinking water arsenic concentration did not explain variability in toenail arsenic concentration. Change in drinking water consumption, however, was significant in predicting differences in toenail arsenic concentration. Stronger correlations between drinking water arsenic concentration and intake and toenail arsenic concentration were observed when two toenail samples were averaged, suggesting that multiple measurements may more accurately reflect exposure. When exposure was categorized into tertiles and other pre-determined categories, 25-40% of exposures were differentially classified. Only a small percentage (<4%), however, were classified as having low exposure using a single measurement and high exposure when an average of two measurements was used. These results suggest that the use of multiple measurements is unlikely to affect exposure classification of individuals into high- or low-exposure groups; however, collection of multiple samples may be advantageous for more refined exposure classification.
在流行病学研究中，脚趾甲剪屑中的砷浓度被用作暴露的生物标志物，通常是基于单次测量代表长期暴露的假设。要使这一假设成立，所测量的砷浓度必须随时间保持稳定，但尚未对时间变异性进行充分评估。本研究旨在评估从饮用水砷含量<100微克/升的人群中采集的多个脚趾甲样本的时间变异性。我们的目标是调查导致生物标志物变异性的因素，并评估单次测量与多次测量在流行病学研究中确定暴露情况的适用性。从美国密歇根州一项砷暴露与膀胱癌病例对照研究中招募的254名参与者采集了多个脚趾甲和饮用水样本；参与者还回答了关于水消耗的问题。平均间隔14个月采集的脚趾甲样本呈正相关，尽管检测到大量变异性（r = 0.43，P<0.0001，n = 236）。饮用水中的砷浓度稳定，饮用水砷浓度的微小变化并不能解释脚趾甲砷浓度的变异性。然而，饮用水消耗量的变化在预测脚趾甲砷浓度差异方面具有显著意义。当对两个脚趾甲样本的平均值进行观察时，发现饮用水砷浓度与摄入量和脚趾甲砷浓度之间的相关性更强，这表明多次测量可能更准确地反映暴露情况。当将暴露分为三分位数和其他预先确定的类别时，25%-40%的暴露被不同分类。然而，只有一小部分（<4%）在单次测量时被归类为低暴露，而在使用两次测量的平均值时被归类为高暴露。这些结果表明，使用多次测量不太可能影响个体在高暴露或低暴露组中的暴露分类；然而，采集多个样本可能有利于更精细的暴露分类。
