Usefulness of Measurement of Serum Iodine Level to Assess the Appropriate Low Iodine Diet Preparation

Seo Young Sohn; Hye Jeong Kim; Hye Won Jang; Sun Wook Kim; Jae Hoon Chung

doi:10.11106/jkta.2012.5.2.143

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Sohn, Kim, Jang, Kim, and Chung: Usefulness of Measurement of Serum Iodine Level to Assess the Appropriate Low Iodine Diet Preparation

Original Article

Journal of Korean Thyroid Association

Journal of Korean Thyroid Association 2012; 5(2): 143-147.

Published online: 28 November 2012

DOI: https://doi.org/10.11106/jkta.2012.5.2.143

Usefulness of Measurement of Serum Iodine Level to Assess the Appropriate Low Iodine Diet Preparation

Seo Young Sohn, Hye Jeong Kim, Hye Won Jang, Sun Wook Kim, Jae Hoon Chung

Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

Correspondence: Jae Hoon Chung, MD, PhD, Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea. Tel: 82-2-3410-3434, Fax: 82-2-3410-3849, thyroid@skku.edu

Received 19 January 2012 Revised 11 April 2012 Accepted 9 May 2012

(open-access):

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background and Objectives

Low-iodine diet (LID) is generally recommended prior to radioactive iodine (RAI) therapy to increase RAI uptake. Recently, we suggested spot urine iodine/creatinine (I/Cr) ratio as a good alternative method replacing measurement of 24 hr urine iodine excretion for the evaluation of appropriate LID preparation. In next step, we studied to evaluate the usefulness of serum iodine concentration comparing with urine iodine concentration and urine I/Cr ratio to assess LID preparation status.

Materials and Methods

We prospectively measured serum iodine concentration, spot urine iodine concentration, and urine I/Cr ratio in 419 patients with differentiated thyroid carcinoma undergoing LID. Appropriate LID preparation was defined as urine I/Cr ratio less than 66.2 ug/gCr.

Results

There were significant correlations between serum iodine and the spot urine iodine concentrations or urine I/Cr ratio; the correlation coefficient was 0.51 for urine iodine concentration and 0.62 for I/Cr ratio (p<0.001). Calculated R² after log-log transformation was 0.45 for I/Cr ratio. The cutoff value of serum iodine concentration was 20.4 ug/L (sensitivity 79.3%, specificity 81.5%) for the evaluation of appropriate LID.

Conclusion

Measurement of serum iodine concentration may be useful as an adjunct parameter for assessing LID preparation, but its sensitivity and specificity were relatively low compared to the urine I/Cr ratio.

Keywords: Iodine, Thyroid carcinoma

Figures and Tables

Fig. 1

The relationship between serum iodine and urine iodine levels. (A) Serum iodine levels were significantly correlated with spot urine iodine levels (r=0.51, p<0.001). (B) Serum iodine levels were significantly correlated w ith spot urine I/Cr ratio (r=0.62, p<0.001).

Fig. 2

The relationship between serum iodine level and urine I/Cr ratio after log-log transformation. R² was calculated by linear regression analysis.

Fig. 3

Receiver-operating characteristic (ROC) analysis to determine the cutoff value of serum iodine for suggesting appropriate low-iodine diet. The area under the curve (AUC) values for serum iodine level was 0.871 (95% confidence interval, 0.832-0.911). The cutoff value of serum iodine level was 20.4 ug/L (sensitivity 79.3%, specificity 81.5%, p<0.001).

Notes

This study was supported by the Korean Thyroid Association-Hanmi Pharm Co. Research Grant (2010) and the Research Grant Number CB-2011-03-02 of the Korean Foundation for Cancer Research.

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