Daily urine iodine excretion while consuming a low-iodine diet in preparation for radioactive iodine therapy in a high iodine intake area

Analytical validation of an inductively coupled plasma mass spectrometry method for urinary iodine concentration measurements in Taiwan

BACKGROUND

Urinary iodine concentration (UIC) measured by Sandell-Kolthoff spectrophotometric method has been used in the Nutrition and Health Surveys in Taiwan but this method is time consuming and produces toxic waste from arsenic trioxide. The aim of this study was to develop and validate an inductively coupled plasma mass spectrometry (ICP-MS) system to determine UIC in Taiwan.

METHODS

Samples and iodine calibrators were diluted 100-fold into an aqueous solution containing Triton X-100, 0.5% ammonia solution, and tellurium (¹²⁸Te) as an internal standard. Digestion prior to analysis was not necessary. Precision, accuracy, serial dilution, and recovery tests were performed. A total of 1243 urine samples covering a wide range of iodine concentrations were measured by both Sandell-Kolthoff method and ICP-MS. Passing-Bablok regression and Bland-Altman plots were used to compare values across methods.

RESULTS

The limit for detection and quantification by ICP-MS was 0.95 μg/L and 2.85 μg/L, respectively. The intra-assay and inter-assay coefficients were <10%, with a recovery range of 95%-105%. The results obtained by ICP-MS and the Sandell-Kolthoff method were highly correlated (Pearson's correlation: r = 0.996, 95% confidence interval [CI]: 0.9950-0.9961, p < 0.001). For UIC between 20 and 1000 μg/L, the y-intercept for the Passing-Bablok regression was -1.9 (95% CI: -2.5599 to -1.3500) and the slope was 1.01 (95% CI: 1.0000-1.0206).

CONCLUSION

This validated ICP-MS system can be used for measuring UIC.

Is a strict restricted-iodine diet necessary for preparation of radioactive iodine therapy?

OBJECTIVE

A restricted-iodine diet (RID) increases the effectiveness of radioiodine therapy (RAIT) by decreasing the body's iodine pool, especially in iodine-rich regions. However, there is no consensus on the RID that should be applied in iodine-deficient areas. This study aims to assess the effect of strict and flexible RID before RAIT.

METHODS

For the study, 144 patients were randomized into the strict or flexible RID group. All patients stopped levothyroxine before RAIT and followed a RID. After 2 weeks of RID, 24-h urine samples were taken. The urinary iodine excretion was compared. In 52 of 144 patients, the spot urine samples were taken before and after RID. The reduction in urinary iodine excretion was compared according to the iodine/creatinine ratio.

RESULTS

Our study included 47 males and 97 females with a mean age of 45 years. After RID in the 24-h urine samples, the mean iodine level was 47.9 µg/day, and both protocols were sufficient to reduce the body iodine pool. There was no significant difference between the strict and the flexible group, 43.06 and 52.89 µg/day (P:0.147). The reduction in urinary iodine excretion was not statistically different in both groups according to spot urine samples (68.20 vs. 60.53%; P:0.377).

CONCLUSION

The flexible RID protocol that less disrupts the patient's quality of life can be preferred for RAIT preparation in iodine-deficient countries.

Impact of low iodine diets on ablation success in differentiated thyroid cancer: A mixed-methods systematic review and meta-analysis

BACKGROUND

Debate remains regarding whether to recommend a low iodine diet (LID) before radioactive-iodine treatment and its duration and stringency. This mixed-methods review aimed to determine if iodine status affects treatment success, the most effective diet to reduce iodine status, and how LID impacts wellbeing.

METHODS

Five electronic databases were searched until February 2021. An effectiveness synthesis (quantitative studies) and views synthesis (qualitative, survey, and experience-based evidence) were conducted individually and then integrated. Quality assessment was undertaken.

RESULTS

Fifty-six quantitative and three qualitative studies were identified. There was greater ablation success for those with an iodine status of &lt;50 mcg/L (or mcg/gCr) compared with ≥250 (odds ratio [OR] = 2.63, 95% confidence interval [CI], 1.18-5.86, n = 283, GRADE certainty of evidence very low). One study compared &lt;50 mcg/L (or mcg/gCr) to 100-199 and showed similar rates of ablation success (OR = 1.59, 95% CI, 0.48-6.15, n = 113; moderate risk of bias). People following a stricter LID before ablation had similar rates of success to a less-strict diet (OR = 0.67, 95% CI, 0.26-1.73, n = 256, GRADE certainty of evidence very low). A stricter LID reduced iodine status more than a less strict (SMD = -0.40, 95% CI, -0.56 to -0.24, n = 816), and reduction was seen after 1 and 2 weeks. The main challenges were a negative impact on psychological health, over restriction, confusion, and difficulty for sub-groups.

CONCLUSIONS

Although a LID of 1-2 weeks reduces iodine status, it remains unclear whether iodine status affects treatment success as only a few low-quality studies have examined this. LIDs are challenging for patients. Higher-quality studies are needed to confirm whether a LID is necessary.

Are ethnic differences, urinary iodine status, lead and cadmium exposure associated with thyroid autoimmunity and hypothyroid status? A cross-sectional study

OBJECTIVE

We aimed to evaluate the effects of different ethnicities and potential environmental exposure on the prevalence of thyroid autoimmune status and hypothyroid status.

DESIGN

The data were obtained from two cross-sectional studies.

PARTICIPANTS

2105 participants in Shanghai (Han) and 772 participants in Yunnan Honghe Prefecture (Han, Yi, Miao and Hani), aged 18-75 were enrolled.

METHODS

Participants underwent several checkups, including urinary iodine concentration, blood lead (BPb) and blood cadmium (BCd), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), thyroid stimulating hormone (TSH) as well as thyroid ultrasonography (US). Thyroid autoimmune status was defined as: antithyroid antibody positive (ATA+): TPOAb + or TgAb+; and ATA + and US+: TPOAb + or TgAb + together with characteristic US features.

RESULTS

The standardised prevalence of thyroid autoimmune positivity in Yunnan were higher than those in Shanghai (TPOAb+: 13.56% vs 8.27%, p<0.001; TgAb+: 9.28% vs 7.09%, p=0.045; ATA+: 16.96% vs 11.10%, p<0.001; ATA + and US+: 8.96% vs 6.64%, p=0.036). For urinary iodine-to-creatinine ratio (UI/Cr), compared with the level of 100.00-199.99 µg/g, the level of ≥300.00 µg/g had a 1.5-fold risk for ATA + and US+ (OR 1.455, p=0.041). The levels of 200.00-299.99 µg/g and ≥300.00 µg/g were positively associated with hypothyroid status (OR 1.509, p=0.002 and OR 1.338, p=0.043). Compared with the first quartiles, the fourth quartiles of BPb were positively associated with TPOAb+: (OR 1.637, p=0.006), ATA+ (OR 1.435, p=0.025), ATA + and US+ (OR 1.641, p=0.013), hypothyroid status (OR 1.467, p=0.013) and TSH levels (B 0.092, p=0.021). The fourth quartile of BCd was positively associated with the prevalence of ATA+ (OR 1.427, p=0.036).

CONCLUSIONS

Higher levels of UI/Cr, BPb and BCd may be associated with thyroid autoimmunity and hypothyroid status.

Low-Iodine Diet of 4 Days Is Sufficient Preparation for 131I Therapy in Differentiated Thyroid Cancer Patients

CONTEXT

No consensus exists about the optimal duration of the low-iodine diet (LID) in the preparation of 131I therapy in differentiated thyroid cancer (DTC) patients.

OBJECTIVE

This work aimed to investigate if a LID of 4 days is enough to achieve adequate iodine depletion in preparation for 131I therapy. In addition, the nutritional status of the LID was evaluated.

METHODS

In this prospective study, 65 DTC patients treated at 2 university medical centers were included between 2018 and 2021. The patients collected 24-hour urine on days 4 and 7 of the LID and kept a food diary before and during the LID. The primary outcome was the difference between the 24-hour urinary iodine excretion (UIE) on both days.

RESULTS

The median 24-hour UIE on days 4 and 7 of the LID were not significantly different (36.1 mcg [interquartile range, 25.4-51.2 mcg] and 36.5 mcg [interquartile range, 23.9-47.7 mcg], respectively, P = .43). On day 4 of the LID, 72.1% of the DTC patients were adequately prepared (24-hour UIE < 50 mcg), and 82.0% of the DTC patients on day 7 (P = .18). Compared to the self-reported regular diet, DTC patients showed a significantly (P < .01) lower percentage of nutrient intake (calories, protein, calcium, iodine, and water) during the LID.

CONCLUSION

The 24-hour UIE on day 4 of the LID did not differ from day 7, and therefore shortening the LID from 7 to 4 days seems justified to prepare DTC patients for 131I therapy in areas with sufficient iodine intake and may be beneficial to maintain a sufficient nutritional intake during DTC treatment.

Development of Databases on Iodine in Foods and Dietary Supplements

Iodine is an essential micronutrient required for normal growth and neurodevelopment; thus, an adequate intake of iodine is particularly important for pregnant and lactating women, and throughout childhood. Low levels of iodine in the soil and groundwater are common in many parts of the world, often leading to diets that are low in iodine. Widespread salt iodization has eradicated severe iodine deficiency, but mild-to-moderate deficiency is still prevalent even in many developed countries. To understand patterns of iodine intake and to develop strategies for improving intake, it is important to characterize all sources of dietary iodine, and national databases on the iodine content of major dietary contributors (including foods, beverages, water, salts, and supplements) provide a key information resource. This paper discusses the importance of well-constructed databases on the iodine content of foods, beverages, and dietary supplements; the availability of iodine databases worldwide; and factors related to variability in iodine content that should be considered when developing such databases. We also describe current efforts in iodine database development in the United States, the use of iodine composition data to develop food fortification policies in New Zealand, and how iodine content databases might be used when considering the iodine intake and status of individuals and populations.

Urinary iodine excretion (UIE) estimated by iodine/creatinine ratio from spot urine in Chinese school-age children

OBJECTIVE

To assess the validity of urinary iodine excretion (UIE) estimated by urinary iodine/creatinine ratio (UI/Cr) from spot urines in Chinese school-age children.

DESIGN

A cross-sectional survey was performed in which twice-repeated collections of 24-h urine, and spot urine samples were obtained within 1 month.

MEASUREMENTS

Urinary iodine concentration (UIC), urinary creatinine concentration (UCr), urine volume (Uvol) of spot and 24-h urine samples were measured. Measured 24-h UIE was calculated from 24-h UIC multiplied by 24-h Uvol, while the estimated 24-h UIE was calculated from spot UI/Cr multiplied by 24-h urinary creatinine excretion (24-h UCrE).

RESULTS

No significant difference was observed in 24-h Uvol between two repeated collections (P = 0·70), while spot UIC, 24-h UIC, spot UI/Cr and measured 24-h UIE were significantly different (P < 0·05). The estimated 24-h UIE was 247 (136-431) μg/day in the first collection, lower than the measured 24-h UIE of 329 (183-536) μg/day (P < 0·001), while no significant difference was observed (P = 0·30) in the second sampling as the estimated 24-h UIE was 355 (168-624) μg/day and the measured 24-h UIE 350 (181-615) μg/day. The spot UIC (r = 0·57, P < 0·001), spot UI/Cr (r = 0·63, P < 0·001) and the estimated 24-h UIE (r = 0·83, P < 0·001) were strongly correlated with the measured 24-h UIE in the first collection. Likewise, in the second sampling, spot UIC (r = 0·60, P < 0·001), spot UI/Cr (r = 0·72, P < 0·001) and the estimated 24-h UIE (r = 0·89, P < 0·001) were also correlated with measured 24-h UIE. The Bland-Altman results indicated 95% of subjects were expected to locate within the limits of agreement (LOA), but showed an underestimation of the urinary iodine excretion by the estimated 24-h UIE. In addition, moderate-to-good agreement was found for the estimated and measured 24-h UIE, with kappa values of 0·55 and 0·66.

CONCLUSIONS

Estimated 24-h UIE by UI/Cr ratio from spot urine could represent a valid and reliable alternative for measured 24-h UIE in estimating iodine excretion in children.

Low iodine diet in differentiated thyroid cancer: a review

Radioactive iodine (RAI) ablation is a beneficial, adjuvant therapy for the management of differentiated thyroid cancer (DTC) after thyroidectomy. The goal of RAI is to destroy remnant thyroid and microscopic cancerous tissue. Radioactive iodine uptake is enhanced by elevating TSH levels and initiating a low iodine diet (LID) prior to ablation. An ideal LID should preferably not exceed 50 mcg/day of dietary iodine for 1-2 weeks, although the duration may be shortened to a week with a structured patient education programme. A pre-ablation spot urinary iodine concentration (UIC) of <100 mcg/l and/or a urinary iodine to creatinine ratio (UICR) of <100 mcg/gCr would support an adequate LID preparation. Hyponatraemia, most likely due to iatrogenic hypothyroidism, is a potential side effect associated with LID and occurs during and a few days after the LID. Although the overall incidence of hyponatraemia is low, patients at high risk (older age, female sex, use of thiazide diuretics) may benefit from serum sodium monitoring. The existing evidence on the impact of LID on RAI ablation has been largely inconsistent due to retrospective study designs and the lack of an objective measurement of urinary iodine levels. Future large prospective randomized control trials are needed to elucidate and confirm the crucial role of LID in achieving successful RAI ablation and greater disease-free survival in DTC.

Low iodine diet for one week is sufficient for adequate preparation of high dose radioactive iodine ablation therapy of differentiated thyroid cancer patients in iodine-rich areas

BACKGROUND

Most current guidelines suggest one or two weeks of low iodine diet (LID) before radioactive iodine ablation therapy (RAIT) to increase its efficacy in differentiated thyroid cancer (DTC) patients after total thyroidectomy. LID duration is particularly important for patients living in iodine excess areas. However, there is no standardized LID protocol and there are limited reports regarding the relationship between LID and ablation outcome. Therefore, we aimed to evaluate the optimal LID duration and define clinical features that affect ablation outcome.

METHODS

A total of 202 papillary thyroid cancer patients with total thyroidectomy preparing for RAIT were enrolled. All patients had undergone two weeks of LID before (131)I administration. Morning spot urine specimens were obtained twice (one week or two weeks after LID, respectively) from each patient. Urine iodine excretion (UIE) values were used to evaluate LID efficacy. Successful ablation was defined using two definitions: (i) no visible uptake on a follow-up diagnostic (131)I scans, and (ii) no visible uptake on a follow-up diagnostic (131)I scans and stimulated serum thyroglobulin (Tg) levels <1 ng/mL.

RESULTS

The UIE median values after LID for one and two weeks were lower than 50 μg/L, and the median UIE values were not significantly different according to the LID duration. Based on the first criterion for successful ablation, 175 of the 195 patients were successfully ablated. There were no significant differences in mean and median UIE levels between the ablated and non-ablated groups after LID for two weeks. The rate of ablation did not differ between the mild and moderate iodine deficient groups. Based on the second criterion for successful ablation, 149 of 188 patients were successfully ablated. The ablation success rate did not differ between UIE levels. When we analyzed clinical factors that affect ablation outcome, serum Tg level at the time of ablation was the only significant variable in multivariate logistic analysis.

CONCLUSION

Strict LID for one week was sufficient to achieve target UIE values for RAIT preparation, even in iodine-rich areas.

The impact of iodinated contrast agent administered during preoperative computed tomography scan on body iodine pool in patients with differentiated thyroid cancer preparing for radioactive iodine treatment

BACKGROUND

Iodine in iodinated contrast agents (ICAs) interferes with radioactive iodine treatment (RAIT) and diagnostic scans in patients with differentiated thyroid carcinoma (DTC) because it can compete with ¹³¹I. Published guidelines recommend delaying RAIT for three to four months in patients who have been exposed to ICA. Spot urinary iodine concentration is a useful marker to reflect the body iodine pool. We investigated the impact of ICAs administered at preoperative computed tomography (CT) scan on the body iodine pool to determine the proper time interval between preoperative CT and RAIT in DTC patients.

METHODS

We performed a retrospective review of 1023 patients with DTC who underwent a preoperative CT scan with ICA, total thyroidectomy, and one week of low-iodine diet in preparation for RAIT. Urine iodine excretion (UIE) was measured in spot urine by inductively coupled plasma mass spectrometry and reported both in simple concentration (μg/L) and divided by gram creatinine (μg/gCr). Patients were divided into five groups by time interval in days between preoperative CT scan and spot urine iodine measurement (A, 31-60 [n=29]; B, 61-90 [n=155]; C, 91-120 [n=546]; D, 121-150 [n=226]; E, 151-180 [n=67]).

RESULTS

The median (interquartile range) of UIE (μg/gCr) in each group was 44.4 (27.7-73.2) in group A, 33.3 (22.8-64.7) in group B, 32.7 (20.8-63.0) in group C, 32.0 (20.6-67.0) in group D, and 30.4 (19.6-70.8) in group E. There was no significant difference between group A and the remaining groups (p>0.05) Also, the proportion of patients who achieved the appropriate UIE for RAIT according to our hospital's cutoff (≤66.2 μg/gCr) was not different between groups (A, 72.4%; B, 76.1%; C, 77.5%; D, 74.8%; E, 74.6%) (p=0.78).

CONCLUSION

This study shows that a UIE of one month after preoperative CT scan with ICA was not higher than that of six months after CT scan in patients who underwent total thyroidectomy for DTC. Thus, current guidelines that recommend delay of RAIT for three to four months after CT scan with ICA should be revisited and future studies to clarify the appropriate time interval between CT scan with ICA and RAIT are warranted.

Low iodine diet for preparation for radioactive iodine therapy in differentiated thyroid carcinoma in Korea

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.

Association between excessive urinary iodine excretion and failure of radioactive iodine thyroid ablation in patients with papillary thyroid cancer

BACKGROUND

A low-iodine diet (LID) is usually recommended for a week or two before radioactive iodine (RAI) ablation therapy in papillary thyroid cancer (PTC) patients after total thyroidectomy. However, it is still controversial whether an LID affects ablation outcomes. We therefore evaluated the association between urinary iodine excretion and the rate of successful ablation and investigated the determinants of successful RAI ablation outcomes.

METHODS

We retrospectively reviewed the records of 295 consecutive patients with PTC who received 1110 MBq RAI remnant ablation therapy with thyroid hormone withdrawal after total thyroidectomy. Successful ablation was defined as either no visible or faint uptake on a follow-up scan (definition 1), or no visible or faint uptake on a follow-up scan and a stimulated thyroglobulin level <2 ng/mL (definition 2).

RESULTS

The proportion of patients with appropriate LID status (defined as a urinary iodine concentration [UIC] <66.2 μg iodine/g creatinine [μg/gCr]) was significantly higher in the successfully ablated group (81% vs. 67%, p=0.03). Based on definition 1, 80.3% (237/295) of patients were successfully ablated. 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 multivariate analysis, a UIC >250 μg/gCr was the only significant variable associated with ablation failure (p=0.002, odds ratio [OR] 4.74 [95% confidence interval (CI) 1.78-12.63]). Based on definition 2, 74.9% (221/295) of patients were successfully ablated. A UIC >250 μg/gCr at RAI administration showed a significant association with ablation failure (p<0.05). The OR of a UIC >250 μg/gCr for ablation failure was 3.88 [CI 1.42-10.57] (p=0.008).

CONCLUSION

Excessive iodine intake (UIC >250 μg/gCr) was associated with poor RAI ablation outcomes. Because this amount of iodine is very high, we propose that the level of strictness of the LID protocol should be modified according to the region that the patient is from and the food that the patient is accustomed to eating. Even in those areas where iodine intake is high, overly strict compliance with an LID protocol is not necessary and simple recommendations to avoid iodine-rich foods would be appropriate.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.