尿比重校正尿碘浓度合理性的实验研究

A study of rationality of correcting urinary iodine concentration by using urine specific gravity

目的 探讨采用尿比重校正尿碘浓度的合理性.方法 分别采用电子天平称重法（简称称重法）和数字式尿液比重折射计法（简称折射计法）测量质量浓度为10～30 g/L的不同无机盐（氯化钠、硫酸钠、磷酸二氢铵）、有机物（尿素、葡萄糖、甘氨酸）水溶液比重,以及尿样外加10～ 30 g/L氯化钠或尿素时尿液比重.采用砷铈催化分光光度法（WS/T 107-2006）、称重法和折射计法测定27份孕妇尿样的尿碘浓度和比重,分别用直接表示、称重法比重校正、折射计法比重校正表示尿碘结果并进行比较.在不同季节分别6批次采集8～10岁学生和孕妇的1次即时尿样,测定折射计法尿比重和尿碘浓度,比较尿碘浓度校正与否的结果.结果 ①称重法测得比重为无机盐（氯化钠、硫酸钠、磷酸二氢铵）水溶液大于相同质量浓度的有机物（尿素、葡萄糖、甘氨酸）水溶液,10 g/L氯化钠溶液的比重（1.008）比30 g/L尿素溶液的比重（1.006）大.②称重法测得3份尿样加10 g/L氯化钠时对应比重分别增加0.006、0.008、0.007,而加10 g/L尿素时对应比重分别增加0.003、0.002、0.004.③27份孕妇尿样尿碘浓度直接表示、称重法比重校正、折射计法比重校正的结果中位数分别为106.4、165.2、211.8 μg/L.④6批次8～10岁学生尿样的折射计法尿比重中位数在1.019 0～1.021 2 g/cm3,尿碘结果直接表示及折射计法比重校正表示的中位数分别在134.5 ～ 181.7、157.7～190.4 μg/L;6批次孕妇尿样的折射计法尿比重中位数在1.013 4～1.017 1 g/cm3,尿碘结果直接表示及折射计法比重校正表示的中位数分别在96.2～138.9、135.2～181.6 μg/L.结论 尿中氯化钠浓度变化是尿比重变化的最主要原因.基于我国人群尿中碘的主要来源是人食用加碘食盐,加碘食盐摄入量直接影响尿比重和尿碘浓度,若以尿比重来校正尿碘浓度,会出现摄入加碘食盐量越低致尿比重越低,尿碘浓度经校正“被增高”越多;反之摄入加碘食盐量越高致尿比重越高,尿碘浓度经校正“被减低”越多的不合理现象,因此不能以尿比重来校正尿碘浓度.

Objective To explore the rationality of correcting urinary iodine （UI） concentration by using urine specific gravity （U-SG）.Methods Weighing method and refractometer method were used respectively to measure specific gravity of 10-30 g/L mass concentration of different inorganic salts （sodium chloride,sodium sulfate,ammonium biphosphate） and organic matters（urea,glucose,glycine） aqueous solution,and urine plus 10-30 g/L sodium chloride or urea.UI concentrations in urine samples of 27 pregnant women respectively were expressed by direct method,weighing method U-SG correction and refractometer method U-SG correction.One random urine sample was collected for six batches in different seasons from children aged 8-10 and pregnant women for determination of U-SG and UI concentration.UI concentration was determined by arsenic cerium catalytic spectrophotometry （WS/T 107-2006）.Results ①Measured by weighing method,specific gravity of inorganic salt （sodium chloride,sodium sulfate,ammonium biphosphate） aqueous solution was significantly greater than that of organic matters （urea,glucose,glycine） aqueous solution which had the same mass concentration.The specific gravity of 10 g/L sodium chloride aqueous solution was 1.008,and that of 30 g/L urea solution was 1.006.②Measured by weighing method,10 g/L sodium chloride was added to 3 urine samples separately.Accordingly the increases of USG were 0.006,0.008 and 0.007,respectively.Otherwise,the increases of U-SG were 0.003,0.002 and 0.004,respectively,when adding 10 g/L urea.~he median results of UI concentrations in urine samples from 27 pregnant women were 106.4,165.2 and 211.8 μg/L,respectively,expressing obtained by direct method,weighing method USG correction and refractometer method U-SG correction.④The determination results of six batches urine collected from children aged 8-10 in different seasons,the median results of U-SG measured by refractometer method were 1.019 0-1.021 2,the median UI concentration results obtained by direct method and refractometer method U-SG correction were 134.5-181.7 μg/L and 157.7-190.4 μg/L.The determination results of six batches urine samples of pregnant women in different seasons,the median results of U-SG measured by refractometer method were 1.013 4 -1.017 1,the median UI concentration results obtained by direct method and refractometer method U-SG correction were 96.2-138.9 μg/L and 135.2-181.6 μg/L.Conclusions The change of sodium chloride concentration in urine is the most important reason for the change of U-SG.In China,the main source of UI is the intake of edible iodized salt.Iodized salt intakes directly affect the U-SG and UI concentration.If the U-SG is used to correct the UI concentration,there will be a phenomena that the lower intake of iodized salt the lower U-SG.So the UI concentration was falsely increased significantly after correction.Conversely higher intakes of iodized salt caused higher U-SG.The UI concentration was falsely reduced significantly after correction.Therefore,U-SG cannot be used to correct the UI concentration.