Value of the Indicators of Urinary Iodine Metabolism in Identifying Iodine Excess during Pregnancy

  Objective  To assess the application value of indicators of urinary iodine metabolism in iden- tifying iodine excess during pregnancy.

  Methods  The clinical data were collected and analyzed of pregnant women undergoing hysterosalpinography(HSG) examination before pregnancy and pregnancy nutrition consultation or management in the Clinical Nutrition Department of Peking Union Medical College Hospital from January to December, 2018. Serum iodine > 90 μg/L was used as the gold standard for diagnosing iodine overdose, and the difference of random urinary iodine, urinary iodine-to-creatinine ratio, and 24-hour urinary iodine excretion were compared between pregnant women with serum iodine > 90 μg/L and pregnant women ≤90 μg/L. Spearman correlation method was used to analyze the correlation between the above indicators of urinary iodine metabolism and serum iodine. The receiver operating characteristic(ROC)curve was used to analyze the clinical value of random urinary iodine, urinary iodine-to-creatinine ratio, and 24-hour urinary iodine excretion in the diagnosis of iodine excess.

  Results  A total of 70 pregnant women meeting the inclusive and exclusive criteria were included in the study.The median value of serum iodine was 138.00(79.00, 510.50) μg/L, 50 cases(71.43%) of serum iodine > 90 μg/L, 20 cases(28.57%) ≤90 μg/L. The random urinary iodine, urinary iodine-to-creatinine ratio, and 24-hour urinary iodine excretion rate of pregnant women with serum iodine > 90 μg/L were significantly higher than those pregnant women with serum iodine ≤90 μg/L(all P < 0.001). Spearman correlation analysis showed that random urinary iodine(r_s=0.749, P < 0.001), urinary iodine-to-creatinine ratio(r_s=0.794, P < 0.001), 24-hour urinary iodine excretion(r_s=0.768, P < 0.001) were all positively related to serum iodine. ROC curve results showed that the area under curve of random urinary iodine(the best cut-off value was 654 μg/L), urinary iodine-to-creatinine ratio(the best cut-off value was 307.5 μg/g), and 24-hour urinary iodine excretion(the best cut-off value was 340.5 μg) on diagnosis iodine excess were 0.732(95% CI: 0.619-0.846), 0.780(95% CI: 0.662-0.898), 0.802(95% CI: 0.697-0.907), respectively, and there was no significant difference between pairwise comparisons(all P > 0.05).

  Conclusions  Women with a history of iodine exposure before pregnancy have a higher rate of excess iodine during pregnancy. Random urinary iodine, urinary iodine-to-creatinine ratio, and 24-hour urinary iodine excretion have certain application value in identifying iodine excess during pregnancy in women with a history of iodine exposure before pregnancy. Because urinary iodine-to-creatinine ratio is convenient to detect, that of > 307.5 μg/g may help to further improve the recognition rate of excess iodine during pregnancy.