J Korean Thyroid Assoc.  2012 Nov;5(2):143-147. 10.11106/jkta.2012.5.2.143.

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

• Sohn SY
• Kim HJ
• Jang HW
• Kim SW
• Chung JH

• KMID: 2095104
• DOI: http://doi.org/10.11106/jkta.2012.5.2.143

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.

Keyword

Iodine; Thyroid carcinoma

MeSH Terms

Diet
Humans
Iodine
Prospective Studies
Sensitivity and Specificity
Thyroid Neoplasms
Iodine

Figure

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  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).

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  Fig. 2 The relationship between serum iodine level and urine I/Cr ratio after log-log transformation. R2 was calculated by linear regression analysis.

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  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).

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