Metabolites in Urine that Interfere with the Sandell-Kolthoff Assay for Urinary Iodine

The Sandell-Kolthoff (SK) assay is the main analytical method used to monitor population iodine nutrition in low- and middle-income countries. This assay can distinguish between populations that are iodine-deficient (median urinary iodine levels below 100 ppb), iodine-sufficient (median urinary iodine levels between 100 and 300 ppb), and iodine- excessive(median urinary iodine levels above 300 ppb). However, the analysis of urine samples with the SK reaction is technically challenging, partly because urine samples must be rigorously pretreated to remove interferents. In the literature, the only urinary metabolite that has been identified as an interferent is ascorbic acid. In this study, we used the microplate SK method to screen thirty-three of the major organic metabolites present in urine. We identified four previously unknown interferents: citric acid, cysteine, glycolic acid and urobilin. For each interferent, we investigated the following factors: (1) nature of interference-positive or negative, (2) threshold concentration for interference, and (3) possible mechanisms of interference. While this paper does not attempt to provide an exhaustive list of all interferents, knowledge of the main interferents allows for targeted removal.

Concentration-dependent Differences in Urinary Iodine Measurements Between Inductively Coupled Plasma Mass Spectrometry and the Sandell-Kolthoff Method

A large amount of historical data regarding urinary iodine concentration (UIC) were measured with the Sandell-Kolthoff (S-K) method for iodine nutrition surveillance. The congruence in urinary iodine measurements between inductively coupled plasma mass spectrometry (ICP-MS) and the S-K method has been debated. A total of 2064 adult urine samples were included in the present study. The UIC measurement results obtained simultaneously by standardized ICP-MS and the S-K method were analyzed. The UIC obtained with ICP-MS was significantly higher than that obtained with the S-K method (158 μg/L vs. 148 μg/L, p < 0.001). The Bland-Altman difference plot showed a small but significant mean difference of 6.12 μg/L between the two methods. The stratified analysis showed that the correlation coefficient was higher in the UIC < 300 μg/L group than the UIC ≥ 300 μg/L group (0.93 vs. 0.88, p = 0.0001). The mean difference between the S-K and ICP-MS methods was positively correlated with the UIC. The ICP-MS and S-K methods were comparable when the UIC was less than 300 μg/L; however, UIC values between 300 and 600 μg/L should be compared with caution after considering the research objective. We do not suggest comparing UICs obtained from the ICP-MS and S-K methods in iodine monitoring studies if the UIC is greater than 600 μg/L.

Analytical evaluation of the new Seal Autoanalyzer 3 High Resolution for urinary iodine determination

Introduction

The aim of the study was to evaluate the analytical performance of the new colorimetric, automatic analyser, Seal AutoAnalyzer 3 High Resolution (Seal AA3 HR) (Seal Analytical, Wisconsin, USA) for urinary iodine measurement.

Materials and methods

This study included testing of several analytical features of the method involving: imprecision (within-run %CVr, between-run %CVb and total laboratory precision %CVl), measurement uncertainty, carryover, linearity and method comparison, with 70 urine samples including the measuring range (20 - 700 µg/L).

Results

Within-run, %CVb and %CVl of two control levels were 2.03% and 3.04%, 0.51% and 2.61%, and 2.09% and 4.01%, respectively. Carryover effect was less than 1%. The linearity was good in the range of urinary iodine values between 60 and 500 µg/L (R² = 0.99). Good agreement of urinary iodine values was found between manual technique and Seal AA3 HR, using Passing-Bablok regression (y = 7.84 (- 3.00 to 15.29) + 0.95 (0.90 to 1.00) x) and Blant-Altman test. Cusum test for linearity indicates that there is no significant deviation from linearity (P > 0.1).

Conclusions

The obtained results proved excellent precision, reproducibility and linearity, comparable to the already used, manual method. The New Seal AA3 HR automatic analyser is acceptable for urinary iodine measurement with very good analytical characteristics and can be used for urinary iodine epidemiological studies of the Croatian population.

Surveillance of Micronutrient Deficiency

Implementing practical and effective surveillance will be essential to control micronutrient deficiency successfully. A number of issues must be resolved, including selecting optimum target groups and appropriate indicators for surveillance, refining interpretive criteria, and defining technically sound and practical methods for data collection and analysis. Consensus on these issues is urgently required to establish effective surveillance that can both support current programmes and document progress toward the global goal of eliminating micronutrient deficiencies.

The assessment of iodine status - populations, individuals and limitations

Iodine deficiency is a significant global health concern, and the single greatest cause of preventable cognitive impairment. It is also a growing public health concern in the UK particularly among pregnant women. Biomarkers such as urinary iodine concentration have clear utility in epidemiological studies to investigate population-level iodine status, but determination of iodine status in individuals is much more problematic with current assays. This article reviews the available biomarkers of iodine status and their relative utility at the level of both populations and individuals for the investigation of iodine deficiency and iodine excess.

Iodine soil dynamics and methods of measurement: a review

Iodine is an essential micronutrient for human health: insufficient intake can have multiple effects on development and growth, affecting approximately 1.9 billion people worldwide. Previous reviews have focussed on iodine analysis in environmental and biological samples, however, no such review exists for the determination of iodine fractionation and speciation in soils. This article reviews the geodynamics of both stable ¹²⁷I and the long-lived isotope ¹²⁹I (t_1/2 = 15.7 million years), alongside the analytical methods for determining iodine concentrations in soils, including consideration of sample preparation. The ability to measure total iodine concentration in soils has developed significantly from rudimentary spectrophotometric analysis methods to inductively coupled plasma mass spectrometry (ICP-MS). Analysis with ICP-MS has been reported as the best method for determining iodine concentrations in a range of environmental samples and soils due to developments in extraction procedures and sensitivity, with extremely good detection limits typically <μg L^-1. The ability of ICP-MS to measure iodine and its capabilities to couple on-line separation tools has the significance to develop the understanding of iodine geodynamics. In addition, nuclear-related analysis and recent synchrotron light source analysis are discussed.

Urinary iodine: comparison of a simple method for its determination in microplates with measurement by inductively-coupled plasma mass spectrometry

The aim of our study was to develop and validate an inexpensive, rapid, easy to use quantitative method to determine urinary iodine without major procurement costs for equipment. The rationale behind introducing this method is the increasing demand for urinary iodine assessments. Our study included 103 patients (76 female, 27 male), age (arithmetic mean) 52 ± 17.3 years. Urinary iodine was determined in microplates by a modification of the Sandell-Kolthoff reaction. The results were compared with inductively-coupled plasma mass spectrometry (ICP-MS) for iodine, considered as reference method. Geometric mean of urinary iodine determined by the Sandell-Kolthoff reaction method was 62.69 μg/l (95% confidence interval 53.16-73.92) whereas by the ICP-MS method it was 65.53 μg/l (95% confidence interval 54.77-78.41). Passing-Bablok regression equations for both methods gave y = 3.374 + 0.873x (y: Sandell-Kolthoff method, x: ICP-MS). Spearman´s correlation coefficient was 0.981, indicating a very high degree of agreement between the two methods. Bland-Altman plots showed no significant systematic difference between the two methods. The modified Sandell-Kolthoff method using microtiter plate technique presented here is a simple, inexpensive semi-automated method to determine urinary iodine with very little toxic waste. Comparison with the ICP-MS-technique yielded a good agreement between the two methods.

Optimization of a New Mass Spectrometry Method for Measurement of Breast Milk Iodine Concentrations and an Assessment of the Effect of Analytic Method and Timing of Within-Feed Sample Collection on Breast Milk Iodine Concentrations

BACKGROUND

Breast milk iodine concentration (BMIC) may be an indicator of iodine status during lactation, but there are few data comparing different analytical methods or timing of sampling. The aims of this study were: (i) to optimize a new inductively coupled plasma mass spectrometry (ICP-MS) method; and (ii) to evaluate the effect of analytical method and timing of within-feed sample collection on BMIC.

METHODS

The colorimetric Sandell-Kolthoff method was evaluated with (a) or without (b) alkaline ashing, and ICP-MS was evaluated using a new (129)I isotope ratio approach including Tellurium (Te) for mass bias correction (c) or external standard curve (d). From iodine-sufficient lactating women (n = 97), three samples were collected within one breast-feeding session (fore-, mid-, and hind-feed samples) and BMIC was analyzed using (c) and (d).

RESULTS

Iodine recovery from NIST SRM1549a whole milk powder for methods (a)-(d) was 67%, 24%, 105%, and 102%, respectively. Intra- and inter-assay coefficients of variation for ICP-MS comparing (c) and (d) were 1.3% versus 5.6% (p = 0.04) and 1.1% versus 2.4% (p = 0.33). The limit of detection (LOD) was lower for (c) (0.26 μg/kg) than it was for (d) (2.54 μg/kg; p = 0.02). Using (c), the median [95% confidence interval (CI) obtained by bootstrap] BMIC (μg/kg) in foremilk (179 [CI 161-206]) and in mid-feed milk (184 [CI 160-220]) were not significantly different (p = 0.017), but were higher than in hindmilk (175 [CI 153-216]; p < 0.001). In foremilk using (d), BMIC was 199 ([CI 182-257]; p < 0.001 vs. (c)). The variation in BMIC comparing (c) and (d) (13%) was greater than variation within feeding (5%; p < 0.001).

CONCLUSIONS

Because of poor recoveries, (a) and (b) should not be used to measure BMIC. Compared with (d), (c) has the advantages of higher precision and a lower LOD. In iodine-sufficient women, BMIC shows low variation within a breast-feeding session, so timing of sampling is not a major determinant of BMIC.

Simultaneous determination of iodide and creatinine in human urine by flow analysis with an on-line sample treatment column

The first system suitable for large-scale screening of iodine deficiency in humans was developed. This is a step towards resolving the outstanding problems of sample preparation and 24 h urine collection.

Determination of iodate by HPLC-UV after on-line electrochemical reduction to iodide

In this study, a novel on-line pre-column electrochemical instrument (PECI) coupled with high-performance liquid chromatography (HPLC) was developed, and a novel method based on PEC-HPLC-UV for amplifying the ultraviolet (UV) response of iodate (IO₃⁻) was studied. Iodate undergoes reduction in the PECI, and the resulting I(-) was injected to an HPLC system and detected by a UV detector. For IO₃⁻ analysis, conditions that can influence the reduction efficiency, including applied potential, pH value and salt concentration, were investigated in detail. In an appropriate condition, the UV response of iodate after passing through PECI was almost 10 times more than that of the initial form with good precision (relative standard deviation 2.0-4.3%). The detection limit and quantity limit were 9 and 20 ng, respectively. It can be concluded that the proposed method is simple and highly sensitive.

Spectrophotometric determination of urinary iodine by the Sandell-Kolthoff reaction subsequent to dry alkaline ashing. Results from the Czech Republic in the period 1994–2002

The Czech Republic is an iodine-deficient area. Insufficient iodine intake was reduced by enriching cooking salt with iodine in the range 20–34mgI/kg. An important indicator for tracking changes in iodine nutrition over time is accurate information about urinary iodine concentrations in the population. In this paper we describe and characterize our method used for the determination of iodine in biological material, which is based on alkaline ashing of urine specimens preceding Sandell-Kolthoff reaction using brucine as a colorimetric marker. The losses of radioiodine added during sample preparation have not exceeded 0.001%. The detection limit is 2.6μgI/L and the limit of quantification is 11.7μgI/L, with intra-assay precision of 4% and inter-assay precision of 4.9%. During the period 1994–2002, the urinary iodine concentration was determined in 29,612 samples in the Institute of Endocrinology. The mean basal urinary iodine concentrations±SD were 115±69μgI/L. Of the samples, 0.7% were in severe (<20μgI/L), 9.6% in moderate (20–49μgI/L), 40.1% in mild (50–99μgI/L), 35.6% in adequate (100–200μgI/L), and 14.0% in more than adequate (>200μgI/L) subsets of iodine nutrition. A statistically significant (p<0.00001) difference was found between mean male (127μgI/L) and female (112μgI/L) urinary iodine, and an inversely proportional trend also exists in the age-related data.

Thyroid size and iodine intake in iodine-repleted pregnant women in Isfahan, Iran

OBJECTIVE

To evaluate the goiter and iodine intake status of pregnant women in Isfahan, after 8 years of iodized salt distribution in Iran.

METHODS

Thyroid staging was assessed by clinical examination, thyroid volume was determined by sonography, and urinary iodine (UI) excretion was assessed by the digestion method in 90 healthy pregnant women (30 in each trimester) and 90 age-matched nonpregnant women selected by random sampling in prenatal and primary health-care clinics. The data were reported as mean +/- standard deviation; P values <0.05 were considered statistically significant.

RESULTS

The mean age of the pregnant and the nonpregnant women was 25.3 and 27.5 years, respectively-no significant difference (P = NS). The clinical goiter prevalence in the pregnant and the nonpregnant groups was 37% and 32%, respectively (P = NS). The mean thyroid volume in the pregnant and nonpregnant women was 7.8 +/- 3.2 and 7.8 +/- 2.8 mL, respectively (P = NS). Urinary iodine (UI) excretion was 20.7 +/- 6.9 mg/dL in pregnant women and 23.7 +/- 7.6 mg/dL in nonpregnant women (P = NS). The prevalence of goiter assessed by sonography was 29% in pregnant women and 21% in nonpregnant women (P = NS). The mean thyroid size in 26 of 90 pregnant women with goiter (thyroid volume >9.2 mL) was 11.8 +/- 2.73 mL and in 19 of 90 nonpregnant women with goiter was 12.36 +/- 1.6 mL (P = NS). The mean thyroid volume was 6.0 +/- 1.7, 9.9 +/- 1.7, 11.8 +/- 2.2, and 18.9 +/- 2.4 mL in the pregnant women with or without goiter at thyroid stages 0, Ia, Ib, and II, respectively. A strong correlation between goiter staging assessed by clinical examination and thyroid volume determined by sonography was found in pregnant (r = 0.77) and nonpregnant (r = 0.78) women (both P<0.000001). Mean UI excretion was 20.9 +/- 7.0, 19.9 +/- 6.8, 20.6 +/- 7.5, and 25.9 +/- 2.3 mg/dL in the pregnant women at thyroid stages 0, Ia, Ib, and II, respectively. In the pregnant and the nonpregnant women, no correlation was found between thyroid stage and UI excretion or between thyroid volume and UI excretion.

CONCLUSION

No iodine deficiency was found in Isfahani pregnant women. Thus, as in most iodine-sufficient areas, thyroid size did not increase during pregnancy. Despite sufficient iodine intake, a moderate prevalence of goiter was noted in pregnant and nonpregnant women. This study also revealed that careful physical examination of the thyroid had diagnostic accuracy similar to sonography.

Determination of iodide in seawater and urine by size exclusion chromatography with iodine-starch complex

A novel method for the determination of iodide by size exclusion chromatography was established. The method was simple and highly sensitive with good precision. Iodide was converted to iodine, then sequestered with starch, and separated from the matrix using a Shim-pack DIOL-150 (250 x 7.9 mm) size exclusion column with methanol-0.01 mol l(-1) aqueous phosphoric acid (10:90, v/v) as mobile phase at 1.2 ml min(-1) and UV detection at 224 nm. The calibration graph was linear from 1.0 ng ml(-1) to 100.0 ng ml(-1) for iodide with a correlation coefficient of 0.9992 (n=6). The detection limit was 0.2 ng ml(-1). The method was successfully applied to the determination of iodide in seawater and urine. The recovery was from 92% to 103% and the relative standard deviation was in the range of 1.5% to 3.7%.

Effects of iodized salt consumption on goiter prevalence in Isfahan: the possible role of goitrogens

OBJECTIVE

To evaluate the success of the Iranian Iodine Deficiency Disorders Committee in achieving World Health Organization (WHO) goals for reducing the prevalence of goiter in children by adding iodine to table salt beginning in 1989.

METHODS

In 1997, 8,000 male and female 6- to 18-year-old students were selected by cluster sampling in schools of Isfahan. Their thyroids were examined by four endocrinologists, and goiter was staged on the basis of the WHO classification. As an index of iodine consumption, urinary iodine concentrations were measured in 3,000 students.

RESULTS

Goiter was observed in 62% of the students. Of the overall study group, 94% had sufficient iodine consumption (urinary iodine concentration of 10.0 microg/dL or more). Of those students who had sufficient iodine intake, 63.2% had goiter. Of the 6% of students with iodine deficiency, 5% had mild, 0.9% had moderate, and only 0.1% had severe iodine deficiency. Goiter was absent in half of the students with severe iodine deficiency. The prevalence of goiter in 6- to 10-year-old children was 65%.

CONCLUSION

Despite sufficient iodine intake, the prevalence of goiter is still high in Isfahan City. Apparently, either this high prevalence has no relationship to iodine deficiency and possibly other unknown goitrogens are involved in the pathogenesis of goiter in Isfahan or the period of iodine intake has been too brief to affect thyroid sizes. Inasmuch as goiter prevalence is also high in the 6- to 10-year-old children, who have had iodized salt available for most of their lives, the second option is less probable. Another possibility is an increased rate of autoimmune thyroid diseases (because of iodine repletion) that resemble goiter during their early stages.

Determination of total iodine in biological material by alkaline ashing and column-switching ion-pair liquid chromatography

A method for the determination of total iodine in biological material has been developed. The method combines alkaline ashing with a selective and sensitive column-switching ion-pair HPLC technique. The ashing procedure which converts the organically bound iodine to iodide is miniaturised and requires only about 100 mg of sample. The first column of the column-switching system is polymer based and can therefore withstand the alkaline pH obtained after ashing. On the analytical column the iodide is separated as an ion-pair with tetrabutyl ammonium hydrogensulphate. The method has been applied to samples from whole blood, urine, liver, lung, carcass, and a sample throughput of at least 50 samples per day can be achieved. Validation studies by spiking experiments showed the precision to be better than 10% R.S.D. for all matrices with recoveries in the range 87-97%. The method has been applied for samples with an iodine content in the range 0.07-1060 microg/g.

An evaluation of urinary measures of iodine and selenium status

The aim of this study was to establish methodology for a survey of the iodine and selenium status of New Zealand residents, more specifically to investigate the correlation between fasting or random casual urine samples and 24 hour urines for iodine and selenium excretion. Sixty-two (31 M, 31 F) adults collected casual, fasting and 24 hour urine samples for analysis of iodide, selenium and creatinine. Plasma and serum samples were collected for analysis of selenium and glutathione peroxidase activity. Results indicated that fasting urine samples, but not casual urines, may give a reasonable estimate of urinary output of iodine and selenium on a population basis, but that 24 hour urines are necessary for diagnosis of iodine deficiency in an individual and for research purposes. The results for iodine also give no support for expressing iodine as the iodide-creatinine ratio, although there was some indication that the selenium-creatinine ratio might be useful. Significant correlations between total daily excretion of selenium and iodine and also for urinary concentrations of the two trace elements in fasting and in 24 hour urine specimens may reflect a relationship of selenium and iodine to body size which may have implications for dietary requirements of these trace elements. Alternatively the correlations may reflect a relationship between dietary intake of the two trace elements in a country in which food concentrations are low, and this needs further investigation.

Rapid and specific high-performance liquid chromatographic method for the determination of iodide in urine

A rapid and specific method for the determination of iodide in urine by high-performance liquid chromatography on an anion-exchange column with electrochemical detection is described. The assay is reproducible as judged by the coefficient of variation of less than 4% at all concentrations used. The limit of detection was 0.1 mumol, and the calibration graph was linear for concentrations between 0.1 and 200 mumol. Using this method, healthy volunteers were found to excrete 69 +/- 39 mumol of iodide per mole of creatinine.

Iodine induced lymphocytic thyroiditis in the BB/W rat: early and late immune phenomena

The effect of iodine excess on thyroid function and on the immunological sequence of events leading to lymphocytic thyroiditis (LT) was studied in the NB subline of BB/W rats to determine the mechanisms by which the level of iodine intake influences the development of LT in this animal model. Iodine supplemented water (500 micrograms/l, Group 1 or 500 mg/l, Group 2) or non-iodine supplemented tap water (Group 3) was given to breeding pairs and their offspring ad libitum. A Wistar rat group, also given tap water (Group 4) served as controls. To determine the immunological sequence of events, the phenotypic nature of the infiltrating thyroid lymphocytes was examined by specific immunoperoxidase staining in BB/W and Wistar rats at 6, 9, 12, and 15 weeks. Antigen-presenting cells and class II (Ia) antigen expression on thyrocytes were also examined. The first immunological event apparent in the iodine-treated BB/W rats was a sharp increase in the number of Ia positive dendritic cells at 9 weeks compared with control BB/W and Wistar rats. In the iodine excess groups dendritic cells were associated with scattered areas of lymphocytic infiltration, comprising predominantly T helper cells (W3/25). T suppressor cells (OX 8) and IL-2 receptor positive activated T-cells (OX 39) were both present in small numbers. B-cells (OX 12) were absent. In addition, thyrocytes did not exhibit Ia antigen expression. By contrast, lymphocytic infiltration was not found at 9 weeks in control BB/W rats.(ABSTRACT TRUNCATED AT 250 WORDS)