Journal List > Korean J Lab Med > v.30(4) > 1011658

Korean J Lab Med. 2010 Aug;30(4):351-356. Korean.
Published online August 30, 2010.  https://doi.org/10.3343/kjlm.2010.30.4.351
Copyright © 2010 The Korean Society for Laboratory Medicine
Determination of Urinary Iodine Concentration by Inductively Coupled Plasma-mass Spectrometry in Thyroid Cancer Patients on Low-iodine Diet
Ji Hyun Lee, M.D.,1 Ok-Ja Ji, M.T.,1 Min-Jung Song, M.D.,1 Hyung-Doo Park, M.D.,1 Hee Kyung Kim, M.D.,2 Sun Wook Kim, M.D.,2 Jae Hoon Chung, M.D.,2 and Soo-Youn Lee, M.D.1
1Department of Laboratory Medicine & Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
2Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

Corresponding author: Soo-Youn Lee, M.D. Department of Laboratory Medicine & Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea. Tel: +82-2-3410-1834, Fax: +82-2-3410-2719, Email: suddenbz@skku.edu
Received January 18, 2010; Revised June 09, 2010; Accepted July 19, 2010.

Abstract

Background

Thyroid cancer patients should be on low-iodine diet (LID) before radioactive iodine therapy (RAIT) to maximize the effect of RAIT. Urinary iodine excretion is the most accurate marker of very recent dietary iodine intake. We developed and evaluated the analytical performance of inductively coupled plasma-mass spectrometry (ICP-MS) to determine urinary iodine concentration.

Methods

We evaluated the linearity, precision, accuracy, and lower limit of quantification (LLOQ) of an ICP-MS method (Agilent 7500ce) to determine urinary iodine concentration in accordance with the Food and Drug Administration (FDA) guidelines for bioanalytical method validation. This method was used to determine and compare the iodine concentration in random urine samples of 120 thyroid cancer patients on LID for 1 week and 80 healthy adults on normal diet.

Results

Our ICP-MS method showed good linearity (1.0-1,913 µg/L; R2>0.999). Both intra-day and inter-day precision CV were within 20% for the LLOQ (1 µg/L) and within 15% for the other concentrations. Accuracy was 110-120% for the LLOQ and 95-115% for the other concentrations. The median concentration of iodine in random urine samples from thyroid cancer patients on LID (38.7 µg/L) was significantly lower than that of healthy subjects (238.8 µg/L) (P<0.0001).

Conclusions

Urinary iodine analysis by ICP-MS showed good linearity, precision, accuracy, wide measuring range of detection, and lower LLOQ. This method will be very useful to evaluate the status of dietary iodine intake and the appropriateness of LID in thyroid cancer patients, thereby maximizing the effect of RAIT.

Keywords: ICP-MS; Urinary iodine; Low-iodine diet; Radioactive iodine therapy; Thyroid cancer

Figures


Fig. 1
Linearity of standard iodine obtained by using inductively coupled plasma-mass spectrometry (ICP-MS).
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Fig. 2
Distribution patterns of urinary iodine in normal adults and thyroid cancer patients on low-iodine diet.

Abbreviation: ICP-MS, inductively coupled plasma-mass spectrometry.

Click for larger image

Tables


Table 1
Instrumental parameters and measurement conditions
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Table 2
Precision and accuracy data for standard iodine obtained by using inductively coupled plasma-mass spectrometry
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Notes

This study was supported by a grant from the Korean Ministry of Education, Science and Technology (FPR08A2-130 of the 21C Frontier Functional Proteomics Program) and a grant from the Korea Healthcare Technology R&D Project, Ministry of Health and Welfare, Republic of Korea (A070001).

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