A study of rationality of correcting urinary iodine concentration by using urine specific gravity / 中华地方病学杂志

ABSTRACT

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.