Low Iodine Diet for Preparation for Radioactive Iodine Therapy in Differentiated Thyroid Carcinoma in Korea

Article information

Endocrinol Metab. 2013;28(3):157-163

Publication date (electronic) : 2013 September 13

doi : https://doi.org/10.3803/EnM.2013.28.3.157

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

Corresponding author: Jae Hoon Chung. Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 135-710, Korea. Tel: +82-2-3410-3434, Fax: +82-2-3410-3849, thyroid@skku.edu

Abstract

Preparation for radioactive iodine (RAI) therapy includes an increased serum thyroid stimulating hormone level and a low iodine diet (LID). Because of extremely high iodine intake, some physicians have advocated a more stringent LID for greater than 2 weeks in Korean patients with thyroid cancer prior to RAI therapy; however, it is very difficult to maintain a stringent LID for a longer period of time. According to recent reports in Korea, a nonstringent, simple LID for only 1 week might be enough prior to RAI therapy, if the patients can be educated intensively by specially trained staff. The measurement of simple urinary iodine concentration (UIC; µg/L) may underestimate daily iodine excretion in patients with a urinary volume of more than 1 L/day and can also be affected by dilution status. Simple UIC had a weaker correlation than the iodine/creatinine (I/Cr) ratio. Therefore, the urinary I/Cr ratio can replace 24-hour urine iodine excretion instead of simple UIC, although it may overestimate iodine intake in patients with malnutrition or poor muscle mass. The measurement of serum iodine level might be useful as an adjunct parameter for assessing LID preparation, but its sensitivity and specificity were relatively low compared to the urinary I/Cr ratio.

Keywords: Radioactive iodine; Iodine; Low iodine diet; Urinary iodine concentration; Urinary iodine excretion

INTRODUCTION

Preparation for radioactive iodine (RAI) therapy includes an increased serum thyroid stimulating hormone (TSH) level (>25 mU/L) and a low iodine diet (LID). An elevated serum TSH level is traditionally achieved by thyroid hormone withdrawal, which may take 4 to 6 weeks; however, thyroid hormone withdrawal may cause a wide range of hypothyroid symptoms and signs and can have a significant impact on patients' daily activities [1-3]. Recombinant human TSH (rhTSH; Thyrogen, Genzyme, Cambridge, MA, USA) can be used as an alternative to thyroid hormone withdrawal to avoid hypothyroidism [1-3]. Another preparation prior to RAI administration is an LID. Most guidelines describing the management of differentiated thyroid cancer (DTC) recommend an LID less than 50 µg/day for 1 to 2 weeks prior to RAI therapy [1,4-8]. Sawka et al. [9] reported in their meta-analysis that ablation rates were higher in patients following an LID than in controls in one study, but, in another study, there was no significant benefit with an LID. They reported that no studies have examined long-term recurrence or mortality rates [9]. In addition, there have been no published studies regarding the appropriate degree and duration of an LID in an iodine-replete area. Recently, some data concerning an LID for preparation for RAI therapy were reported in Korea.

IS IODINE EXCESS TRUE IN MOST KOREAN POPULATIONS?

According to the World Health Organization epidemiological criteria for assessing iodine nutrition (2007), a median urinary iodine concentration (UIC) of 100 to 199 µg/L indicates adequate iodine intake in men, school-age children (≥6 years), and nonpregnant or lactating women. A median UIC of greater than 300 µg/L indicates excessive iodine intake, which may increase the risk of adverse health consequences [10]. More than 90% of dietary iodine is excreted in the urine, and UIC is considered an index of recent iodine intake. In nonpregnant, nonlactating women, a UIC of 100 µg/L corresponds roughly to a daily iodine intake of approximately 150 µg under steady-state conditions [10].

Kim et al. [11] reported that the average estimated iodine intake in 278 healthy Korean adults was 479 µg/day, and their average urinary iodine/creatinine (I/Cr) ratio was 674 µg/gCr, using an iodide selective electrode. Recently, Chung et al. [3] evaluated median UIC and median urinary I/Cr ratio in 1,072 euthyroid patients with benign thyroid nodules. Their median UIC was 358 µg/L, with a range from 24 to 9,224 µg/L, and the median urinary I/Cr ratio was 341 µg/gCr (data not published). In their study, UIC was measured by inductively coupled plasma mass spectrometry using an Agilent 7500 series instrument (Agilent Technologies Inc., Tokyo, Japan), which has been demonstrated to be extremely accurate in measuring UIC [12]. These levels are higher than those reported in other countries, except some regions in Japan. Because of extremely high iodine intake in most Korean populations, some physicians have advocated a more stringent LID for greater than 2 weeks in Korean DTC patients preparing for RAI therapy [13-15]; however, this is very difficult, and it seems to be impractical to maintain a stringent LID for a longer time prior RAI therapy. Therefore, I am going to discuss the degree and duration of an LID as a preparation for RAI therapy in Korean patients with DTC.

IS A STRICT LOW-IODINE DIET NECESSARY AND REQUIRED FOR SUCCESSFUL RAI THERAPY?

Most guidelines regarding the management of DTC recommend an LID of less than 50 µg/day for 1 or 2 weeks prior to RAI therapy [1,4-8]. The European Association of Nuclear Medicine Therapy Committee (2008) recommends postponement of RAI therapy when the stable UIC is above 150 to 200 µg/L, which is believed to reflect a clinically relevant excess of iodine [5]. The theoretical basis is that low plasma iodide concentrations may increase the expression of the sodium-iodine symporter gene and result in increased RAI uptake in remnant thyroid tissue or cancer cells [16]; however, this recommendation is not based on outcome studies. Although several studies have examined the impact of an LID on success rates of RAI therapy, the results are inconsistent [17-19]. Pluijmen et al. [17] found that low UIC was associated with an improvement in the success rate of ablation. They reported that successful ablation was more frequent in patients who were on an LID than control patients who were on a standard diet (63% vs. 48% with 24-hour urine iodine excretion rates of 26.6 and 158.8 µg/day, respectively) [17]. In contrast, Morris et al. [18] and Tala Jury et al. [19] found no difference in UIC between ablated or nonablated patients. Recently, Sohn et al. [20] reported that the ablation rate was significantly lower in patients who had a UIC >250 µg/gCr at the time of RAI ablation (P<0.05). In a multivariate analysis, a UIC >250 µg/gCr was the only significant variable associated with ablation failure (P=0.001; odds ratio, 4.53 to 4.57; 95% confidence interval [CI], 1.73 to 11.9); however, the ablation rates were not different in patients with a UIC <250 µg/gCr (P for trend <0.05) (Fig. 1). They suggested that a strict LID was not necessary to achieve a successful ablation. Therefore, a nonstringent, simple LID might be adequate preparation for RAI therapy, even in an iodine-replete area such as Korea.

Fig. 1

Ablation outcomes. (A) The definition of ablation was negative or faint uptake on a diagnostic whole-body scan. The ablation rate significantly decreased as urinary iodine excretion increased (P for trend=0.008). (B) The definition of ablation was negative or faint uptake on a diagnostic whole-body scan plus a stimulated serum thyroglobulin less than 2 ng/mL. The ablation rate significantly decreased as urinary iodine excretion increased (P for trend=0.013). Adapted from Sohn et al. Thyroid 2013;23:741-7, with permission from Mary Ann Liebert, Inc. [20].

CAN THE I/CR RATIO FROM A SPOT-URINE SAMPLE REPLACE 24-HOUR URINE IODINE EXCRETION TO EVALUATE THE APPROPRIATENESS OF A LOW-IODINE DIET FOR PREPARATION FOR RAI THERAPY?

Most iodine absorbed in the body is eventually excreted in the urine. Therefore, UIC is a good marker of very recent dietary iodine intake. Measurement of UIC in 24-hour urine is considered the gold standard to evaluate the appropriateness of LID [21]; however, 24-hour urine collection is inconvenient and cumbersome for patients [12]. An alternative method is to measure iodine concentration in a random spot-urine, but this is influenced by the time of collection and the degree of urine dilution [22]. There is a circadian rhythm to urinary iodine excretion, and urinary iodine excretion is lowest between 8:00 AM and 11:00 AM and reaches peak levels 4 to 5 hours after main meals [22]. Therefore, a fasting morning urine is recommended to measure the UIC [10]. No simple reliable index in a spot-urine sample has been developed to replace the 24-hour urinary iodine excretion.

Kim et al. [23] demonstrated that the I/Cr ratio from a spot-urine sample could serve as a useful and reliable alternative to 24-hour urine collection to evaluate the appropriateness of an LID prior to RAI therapy. They enrolled 193 patients and collected 24-hour urine samples (µg/day) and fasting spot-urine samples (µg/L and µg/gCr). There were statistically significant correlations between the 24-hour urinary iodine excretion and the two spot-urine-based indices (correlation coefficient, 0.539 for simple UIC; 0.773 for I/Cr ratio, P<0.001) (Fig. 2). When a 24-hour urinary iodine excretion of >150 µg/day was defined as a poor LID and receiver operating characteristic analysis was performed, the cutoff of the I/Cr ratio for poor LID was >66.2 µg/gCr (sensitivity 96.4%, specificity 83.6%, positive predictive value 50.0%, and negative predictive value 99.3%). A simple UIC has been proposed as a marker for iodine status in epidemiological studies [24-26]; however, this measurement could underestimate daily iodine excretion in patients with a urinary volume of more than 1 L/day and be affected by dilution status. Kim et al. [23] found that a simple UIC had a weaker correlation than the I/Cr ratio; however, the I/Cr ratio has a limitation in that it may overestimate iodine intake in patients with malnutrition or poor muscle mass because of low Cr levels.

Fig. 2

(A) The relationship between the iodine/creatinine (I/Cr) ratio from a spot-urine and iodine excretion from a 24-hour urine collection. The horizontal dotted line denotes the cutoff for the poor status of a low-iodine-diet preparation for radioiodine therapy based on a 24-hour urine iodine excretion, which was set at 150 µg/day. The vertical dotted line is the proposed cutoff of the 'I/Cr ratio' from a spoturine, which was set at 66.2 µg/gCr. (B) The correlation after log-log transformation of the data. R² was computed by regression analysis. Adapted from Kim et al. Clin Endocrinol (Oxf) 2010;73:114-8, with permission from Blackwell Publishing [23].

OPTIMAL LENGTH OF A LOW-IODINE DIET FOR PREPARATION OF RAI THERAPY: 1 WEEK VS. 2 WEEKS

The American Thyroid Association and Korean Thyroid Association recommend an LID for 1 to 2 weeks for patients undergoing RAI remnant ablation, particularly for those patients with high iodine intake [1,8]. In contrast, the European Thyroid Association recommends an LID for 3 weeks prior to RAI therapy [4]. Several protocols exist for an LID, but there are no standardized guidelines for the duration of an LID prior to RAI therapy. Iodine intake varies depending on the region and patients' diet patterns. The reduction by 1 week for an LID has a large impact on the patients' quality of life. A longer duration of an LID tries their patience, and some patients reach the end of endurance. A longer duration of LID can even affect patients negatively.

There are four articles dealing with the duration of an LID (1 week vs. 2 weeks) prior to RAI therapy. Two articles reported in Korea suggested that an LID for 1 week was enough to achieve an acceptable reduction of UIE [15,27]. On the contrary, another two articles reported in the USA and Japan suggested an LID for 2 weeks was superior to 1 week to achieve the targeted reduction in UIC [13,14]. Kim et al. [27] suggested that a 1-week strict LID was enough to decrease the level of UIC in preparation for RAI therapy, even in an iodine-sufficient area such as Korea. They prospectively designed and enrolled 19 patients with DTC preparing for RAI therapy. Patients went on a strict LID for 2 weeks prior to RAI administration. The daily first spot-urine in the morning was collected and stored at -20℃ for 2 weeks from the first day of the LID to the day of RAI administration. Patients were educated by specially trained nurses and dieticians for 2 hours before the start of the LID. They were informed about the foods that were allowed and not allowed. They were given a 3-day sample menu specifically designed for patients living in Korea and the contact information for dietary questions. The UIC (µg/gCr) decreased significantly from day 0 (576.9±825.5) to day 7 (26.7±16.2) and day 14 (19.5±8.8) (P<0.05) (Fig. 3). On day 6, the UIC decreased below the cutoff level (66.2 µg/gCr) by both 95% CI (0 to 60.8 µg/gCr) and 90th percentile (51.9 µg/gCr). Roh et al. [15] also demonstrated that a stringent LID for 1 week resulted in a better UIC (I/Cr ratio) compared with a less stringent LID for 2 weeks; however, they cautiously suggested that a stringent LID for 2 weeks is expected to be more desirable. On the contrary, Park and Hennessey. [13] suggested that an acceptable reduction (<100 µg/gCr) of UIC was achieved in 41% of patients with a 1-week LID and in 71% patients with a 2-week LID. They reported that the mean UIC (I/Cr ratio) was significantly lower in 24 patients who followed a 2-week LID (84.7±44.0) compared to 21 patients on a 1-week LID (199.9±169.5, P<0.01). Tomoda et al. [14] also suggested that a targeted reduction of UIC (<100 µg/gCr) was achieved in 26% of patients with a 1-week and in 70% with a 2-week LID. They reported that UIC (I/Cr ratio) was lower after 2 weeks of LID (17 patients; 63.1±38.7) than after 1 week of LID treatment (15 patients; 119.4±55.9) when the patients followed a stringent LID. In both studies, LID was explained to the patients after surgery and they were sent home with a simple, one-page list of dietary recommendations. A possible explanation for this discrepancy between Kim (Korea), Park (USA), and Tomoda (Japan) might be the intensity and compliance to the LID by patients. In conclusion, LID for 1 week may be enough prior to RAI therapy even in an iodine-replete area, if the patients can be educated intensively by specially trained staffs and their compliance can be regularly checked and reinforced.

Fig. 3

Changes in daily urine iodine excretion by the iodine/creatinine (I/Cr) ratio during a low iodine diet in preparation for radioiodine therapy among differentiated thyroid cancer patients. The I/Cr ratio decreased significantly from day 0 (576.9±825.5) to day 7 (26.7±16.2) and day 14 (19.5±8.8) (P<0.05). On day 6, the I/Cr ratio decreased below the cutoff level (66.2 µg/gCr) by both 95% confidence interval (0 to 60.8 µg/gCr) and 90th percentile (51.9 µg/gCr). Adapted from Kim et al. Clin Endocrinol (Oxf) 2011;75:851-6, with permission from Blackwell Publishing [27].

Levothyroxine might be a significant source of dietary iodine in patients undergoing rhTSH-stimulated RAI therapy. Park and Hennessey [13] reported in a previous study that the urinary iodine excretion (I/Cr ratio) after a 2-week LID was different between patients without levothyroxine (59.6±76.0) and with levothyroxine (84.7±44.0, P<0.01).

CAN THE MEASUREMENT OF THE SERUM IODINE LEVEL REPLACE URINE IODINE EXCRETION IN THE EVALUATION OF THE APPROPRIATENESS OF A LOW-IODINE DIET FOR PREPARATION FOR RAI THERAPY?

Sohn et al. [28] suggested that the measurement of the serum iodine level might 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. They found significant correlations between the serum iodine level and the spot UIC (µg/L) or I/Cr ratio (µg/gCr) (correlation coefficients, 0.51 for UIC; 0.62 for I/Cr ratio; P<0.001) (Figs. 4, 5). The cutoff value for the serum iodine level was 20.4 µg/L (sensitivity 79.3%, specificity 81.5%) for the evaluation of an appropriate LID.

Fig. 4

The relationship between serum iodine and urine iodine levels. (A) Serum iodine levels were significantly correlated with spoturine iodine levels (r=0.51, P<0.001). (B) Serum iodine levels were significantly correlated with the spot-urine iodine/creatinine (I/Cr) ratio (r=0.62, P<0.001). Adapted from Sohn et al. J Korean Thyroid Assoc 2012;5:143-7 [28].

Fig. 5

The relationship between serum iodine level and urine iodine/creatinine (I/Cr) ratio after log-log transformation. R² was calculated by linear regression analysis. Adapted from Sohn et al. J Korean Thyroid Assoc 2012;5:143-7 [28].

CONCLUSIONS

A nonstringent, simple LID for only 1 week might be enough prior to RAI therapy, if the patients can be educated intensively. The urinary I/Cr ratio can replace 24-hour urine iodine excretion instead of simple UIC, The measurement of serum iodine level might be useful as an adjunct parameter for assessing LID preparation, but its sensitivity and specificity were relatively low compared to the urinary I/Cr ratio.

ACKNOWLEDGMENTS

I would like to express my sincere appreciation to Dr. Hee Kyung Kim, Dr. Seo Young Sohn, Dr. Na Kyung Kim, and Professor Sun Wook Kim for discussions regarding their raw data.

Notes

No potential conflict of interest relevant to this article was reported.

References

1. American Thyroid Association (ATA) Guidelines Taskforce on Thyroid Nodules and Differentiated Thyroid Cancer. Cooper DS, Doherty GM, Haugen BR, Kloos RT, Lee SL, Mandel SJ, Mazzaferri EL, McIver B, Pacini F, Schlumberger M, Sherman SI, Steward DL, Tuttle RM. Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid 2009;19:1167–1214. 19860577.

2. Chen MK, Doddamane I, Cheng DW. Recombinant human thyroid-stimulating hormone as an alternative for thyroid hormone withdrawal in thyroid cancer management. Curr Opin Oncol 2010;22:6–10. 19844179.

3. Chung JH. Use of recombinant human TSH (rhTSH) In : Baek JH, Chang HS, Choi SH, Chung JH, Kim TY, Kim WB, Ryu JS, Shong YK, eds. Proceedings of the First Asian Master Course of Thyroid Cancer; 2011 September 1-3; Seoul, Korea. Seoul: Korean Thyroid Association; 2011. p. 143–149.

4. Pacini F, Schlumberger M, Dralle H, Elisei R, Smit JW, Wiersinga W. European Thyroid Cancer Taskforce. European consensus for the management of patients with differentiated thyroid carcinoma of the follicular epithelium. Eur J Endocrinol 2006;154:787–803. 16728537.

5. Luster M, Clarke SE, Dietlein M, Lassmann M, Lind P, Oyen WJ, Tennvall J, Bombardieri E. European Association of Nuclear Medicine (EANM). Guidelines for radioiodine therapy of differentiated thyroid cancer. Eur J Nucl Med Mol Imaging 2008;35:1941–1959. 18670773.

6. Gharib H, Papini E, Paschke R, Duick DS, Valcavi R, Hegedüs L, Vitti P. AACE/AME/ETA Task Force on Thyroid Nodules. American Association of Clinical Endocrinologists, Associazione Medici Endocrinologi, and European Thyroid Association Medical guidelines for clinical practice for the diagnosis and management of thyroid nodules: executive summary of recommendations. Endocr Pract 2010;16:468–475. 20551008.

7. Gharib H, Papini E, Paschke R, Duick DS, Valcavi R, Hegedüs L, Vitti P. AACE/AME/ETA Task Force on Thyroid Nodules. American Association of Clinical Endocrinologists, Associazione Medici Endocrinologi, and European Thyroid Association medical guidelines for clinical practice for the diagnosis and management of thyroid nodules: executive summary of recommendations. J Endocrinol Invest 2010;33(5 Suppl):51–56. 20543551.

8. Yi KH, Park YJ, Koong SS, Kim JH, Na DG, Ryu JS, Park SY, Park IA, Baek CH, Shong YK, Lee YD, Lee J, Lee JH, Chung JH, Jung CK, Choi SH, Cho BY. Revised Korean Thyroid Association Management Guidelines for patients with thyroid nodules and thyroid cancer. J Korean Thyroid Assoc 2010;3:65–96.

9. Sawka AM, Ibrahim-Zada I, Galacgac P, Tsang RW, Brierley JD, Ezzat S, Goldstein DP. Dietary iodine restriction in preparation for radioactive iodine treatment or scanning in well-differentiated thyroid cancer: a systematic review. Thyroid 2010;20:1129–1138. 20860420.

10. International Council for Control of Iodine Deficiency Disorders. UNICEF. World Health Organization. Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers 3rd edth ed. Geneva: World Health Organization; 2007.

11. Kim JY, Moon SJ, Kim KR, Sohn CY, Oh JJ. Dietary iodine intake and urinary iodine excretion in normal Korean adults. Yonsei Med J 1998;39:355–362. 9752802.

12. Knudsen N, Christiansen E, Brandt-Christensen M, Nygaard B, Perrild H. Age- and sex-adjusted iodine/creatinine ratio. A new standard in epidemiological surveys? Evaluation of three different estimates of iodine excretion based on casual urine samples and comparison to 24 h values. Eur J Clin Nutr 2000;54:361–363. 10745289.

13. Park JT 2nd, Hennessey JV. Two-week low iodine diet is necessary for adequate outpatient preparation for radioiodine rhTSH scanning in patients taking levothyroxine. Thyroid 2004;14:57–63. 15009915.

14. Tomoda C, Uruno T, Takamura Y, Ito Y, Miya A, Kobayashi K, Matsuzuka F, Amino N, Kuma K, Miyauchi A. Reevaluation of stringent low iodine diet in outpatient preparation for radioiodine examination and therapy. Endocr J 2005;52:237–240. 15863954.

15. Roh JH, Kim BI, Ha JS, Chang SJ, Shin HY, Choi JH, Kim DM, Kim CS. Comparison of urine iodine/creatinine ratio between patients following stringent and less stringent low iodine diet for radioiodine remnant ablation of thyroid cancer. Nucl Med Mol Imaging 2006;40:322–326.

16. Uyttersprot N, Pelgrims N, Carrasco N, Gervy C, Maenhaut C, Dumont JE, Miot F. Moderate doses of iodide in vivo inhibit cell proliferation and the expression of thyroperoxidase and Na+/I- symporter mRNAs in dog thyroid. Mol Cell Endocrinol 1997;131:195–203. 9296378.

17. Pluijmen MJ, Eustatia-Rutten C, Goslings BM, Stokkel MP, Arias AM, Diamant M, Romijn JA, Smit JW. Effects of low-iodide diet on postsurgical radioiodide ablation therapy in patients with differentiated thyroid carcinoma. Clin Endocrinol (Oxf) 2003;58:428–435. 12641625.

18. Morris LF, Wilder MS, Waxman AD, Braunstein GD. Reevaluation of the impact of a stringent low-iodine diet on ablation rates in radioiodine treatment of thyroid carcinoma. Thyroid 2001;11:749–755. 11525267.

19. Tala Jury HP, Castagna MG, Fioravanti C, Cipri C, Brianzoni E, Pacini F. Lack of association between urinary iodine excretion and successful thyroid ablation in thyroid cancer patients. J Clin Endocrinol Metab 2010;95:230–237. 19858316.

20. Sohn SY, Choi JY, Jang HW, Kim HJ, Jin SM, Kim SW, Suh S, Hur KY, Kim JH, Chung JH, Kim SW. Association between excessive urinary iodine excretion and failure of radioactive iodine thyroid ablation in patients with papillary thyroid cancer. Thyroid 2013;23:741–747. 23205883.

21. Baloch Z, Carayon P, Conte-Devolx B, Demers LM, Feldt-Rasmussen U, Henry JF, LiVosli VA, Niccoli-Sire P, John R, Ruf J, Smyth PP, Spencer CA, Stockigt JR. Guidelines Committee, National Academy of Clinical Biochemistry. Laboratory medicine practice guidelines. Laboratory support for the diagnosis and monitoring of thyroid disease. Thyroid 2003;13:3–126. 12625976.

22. Rasmussen LB, Ovesen L, Christiansen E. Day-to-day and within-day variation in urinary iodine excretion. Eur J Clin Nutr 1999;53:401–407. 10369497.

23. Kim HK, Lee SY, Lee JI, Jang HW, Kim SK, Chung HS, Tan AH, Hur KY, Kim JH, Chung JH, Kim SW. Usefulness of iodine/creatinine ratio from spot-urine samples to evaluate the effectiveness of low-iodine diet preparation for radioiodine therapy. Clin Endocrinol (Oxf) 2010;73:114–118. 20050860.

24. Konno N, Yuri K, Miura K, Kumagai M, Murakami S. Clinical evaluation of the iodide/creatinine ratio of casual urine samples as an index of daily iodide excretion in a population study. Endocr J 1993;40:163–169. 7951490.

25. Thomson CD, Smith TE, Butler KA, Packer MA. An evaluation of urinary measures of iodine and selenium status. J Trace Elem Med Biol 1996;10:214–222. 9021672.

26. Bourdoux P. Evaluation of the iodine intake: problems of the iodine/creatinine ratio: comparison with iodine excretion and daily fluctuations of iodine concentration. Exp Clin Endocrinol Diabetes 1998;106(Suppl 3):S17–S20. 9865547.

27. Kim HK, Lee SY, Lee JI, Jang HW, Kim SK, Chung HS, Tan AH, Hur KY, Kim JH, Chung JH, Kim SW. Daily urine iodine excretion while consuming a low-iodine diet in preparation for radioactive iodine therapy in a high iodine intake area. Clin Endocrinol (Oxf) 2011;75:851–856. 21707689.

28. Sohn SY, Kim HJ, Jang HW, Kim SW, Chung JH. Usefulness of measurement of serum iodine level to assess the appropriate low iodine diet preparation. J Korean Thyroid Assoc 2012;5:143–147.

Article information Continued

(open-access, http://creativecommons.org/licenses/by-nc/3.0/) :

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.