Abstract
A large amount of historical data regarding urinary iodine concentration (UIC) were measured with the Sandell-Kolthoff (S-K) method for iodine nutrition surveillance. The congruence in urinary iodine measurements between inductively coupled plasma mass spectrometry (ICP-MS) and the S-K method has been debated. A total of 2064 adult urine samples were included in the present study. The UIC measurement results obtained simultaneously by standardized ICP-MS and the S-K method were analyzed. The UIC obtained with ICP-MS was significantly higher than that obtained with the S-K method (158 μg/L vs. 148 μg/L, p < 0.001). The Bland-Altman difference plot showed a small but significant mean difference of 6.12 μg/L between the two methods. The stratified analysis showed that the correlation coefficient was higher in the UIC < 300 μg/L group than the UIC ≥ 300 μg/L group (0.93 vs. 0.88, p = 0.0001). The mean difference between the S-K and ICP-MS methods was positively correlated with the UIC. The ICP-MS and S-K methods were comparable when the UIC was less than 300 μg/L; however, UIC values between 300 and 600 μg/L should be compared with caution after considering the research objective. We do not suggest comparing UICs obtained from the ICP-MS and S-K methods in iodine monitoring studies if the UIC is greater than 600 μg/L.
Highlights
Iodine is an essential component of thyroid hormones and normally obtained by the consumption of foods that contain iodine or iodized salt, and either low or high iodine intake may lead to thyroid disorders [1]
The Bland-Altman plot showed that the Urinary iodine concentration (UIC) measured by ICPMS was 6.12 μg/L higher than that measured by the S-K method
That difference was acceptable in clinical examination; we considered that the S-K and inductively coupled plasma mass spectrometry (ICP-MS) methods showed good congruence and the test results of the two methods could be compared directly
Summary
Iodine is an essential component of thyroid hormones and normally obtained by the consumption of foods that contain iodine or iodized salt, and either low or high iodine intake may lead to thyroid disorders [1]. Different techniques for the determination of urinary iodine, such as chemical methods and inductively coupled plasma mass spectrometry (ICP-MS), have been developed [7]. UIC is commonly determined spectrophotometrically using the Sandell-Kolthoff reaction (SK), or by ICP-MS [8]. The S-K method is cumbersome and time consuming, with significant chemical hazards such as arsenic and cerium. As the S-K method relies on chemical kinetics for determination of iodine concentration, the assay is susceptible to form organic species which may chelate cerium and alter the reaction rate [9, 10]. The ICP-MS method is fast and accurate, offers precision that is equal to the S-K method, enables easier sample preparation, and has the potential for simultaneous multielement analysis [11]
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