Measurement of urinary iodide levels by ion-selective electrode: Improved sensitivity and specificity by chromatography on
The last national nutritional
survey (NHANES III 1988-1994) revealed that 15% of the
To encourage physicians to perform routine urine I determination in their practice, a simple method will be described to accurately measure urine I levels. This technique uses quantification of iodide by a potentiometric method, using an ion-selective electrode (ISE). Urinary iodide is measured by the electromotive force (EMF) generated on the iodide-selective electrode due to the presence of iodide in the urine sample. Within a certain range of iodide concentrations, there is a linear relationship between the logarithm of iodide concentration and the EMF generated. The concentration of chloride in urine is usually one millionfold higher than iodide and there is a significant interference by chloride in the analysis of urinary iodide by the ISE method. To prevent this interference, purification of the urine sample by anion exchange chromatography is performed prior to ISE measurement. This assay is simple, rapid, with results within one hour, if the ISE measurement is performed in the physician’s office. We also present preliminary data on an I-loading test to assess I sufficiency of the whole human body.
II. Motivating factor in the development of the assay
Mainland Japanese women have a very low incidence and prevalence of FDB and breast cancer (11). Several investigators have proposed that the essential element I was the protective factor in mainland Japanese (2-8). If indeed, the essential element I is the postulated protective factor, the administration of I to American women in amounts equivalent to that consumed by mainland Japanese women would be expected to protect them from breast cancer and improve FDB, as previously proposed by Stadel for breast cancer (12) and confirmed for FDB by Ghent et al (5). Based on data supplied by the Japanese Ministry of Health, the average daily I intake in mainland Japanese is 13.8 mg (13).
We evaluated the effect of 2 drops of Lugol solution in tablet form containing 5 mg of iodine and 7.5 mg iodide as the potassium salt, (Iodoral®, Optimox Corporation, Torrance, CA), administered daily for 3 months to 10 normal women. Informed consent was obtained from all subjects participating in the studies described in this manuscript. This supplement had no adverse effect on ultrasonometry of the thyroid gland, the serum levels of thyroid hormones, blood chemistry, hematology, and urine analysis (13). This form and amount of I was chosen because it was widely prescribed during the early and mid 1900’s for I replacement therapy (13-16). The amount of 12.5 mg of I present in 2 drops of Lugol is very close to the estimated mean daily intake of 13.8 mg I by mainland Japanese (13).
According to the medical literature,
urinary I level is the most valid index of I intake (17, 18). Using a commercial laboratory (Doctor’s Data
Following one month of daily ingestion of one tablet of Iodoral®, the excretion of I increased to 36-96% of the oral amount in 4 of the subjects with a mean of 50% in the 5 subjects (Table I). Female Subject #2 excreted only 10% of the oral dose after one month of supplementation. She had the lowest baseline I level (0.022 mg/24 hr) and the greatest I retention after one and 30 days. The only distinctive feature of this subject was mammomegaly (size 40D). This would suggest a very important role of the mammary glands in the requirement for I by the whole human body. To our knowledge, the above findings have not been previously reported. The implication of such observation is that an I-loading test could be developed to assess not just thyroid sufficiency but I requirement of the whole human body. However, for such a test to be practical, one month duration is too long. So, the next alternative was to progressively increase the amount of I in a single dose and to measure urinary I excretion in order to find the amount of ingested I that would result in the greatest between individual differences of urine I levels, as an index of degree of whole body I sufficiency. The standard deviation from the mean value could be used as an index of the between-individual variations.
Another group of 6 subjects, 3 males and 3 females were evaluated with 24 hour urinary I levels before and after ingesting one, two and three tablets of the same preparation. The subjects retained approximately 80% of the I content of one and two tablets (Table II). But with three tablets containing 37.5 mg of I, there was a twofold difference in I excretion, with a range of 6.8 to 14 mg I (18%-37%) (Table II). The means ± SD of urinary I levels (mg/24 hr.) for the 3 doses of I were: 2.8 ± 0.14 (C.V. = 5%) for one tablet of Iodoralâ; 5.4 ± 0.35 (C.V. = 6.5%) for 2 tablets; and 9.48 ± 4.6 (C.V. = 48.5%) for 3 tablets. There was a 10 fold increase in the coefficient of variation around the mean value at 3 tablets of the I supplement, compared to one and two tablets. Subject #3 who retained the most I, with only 6.8 mg (18%) in the 24 hour urine collection, suffered from severe FDB, again pointing at the mammary glands as an important organ of I utilization. These results suggest that the measurement of urinary I levels before and after administration of three tablets of Iodoralâ, could be used as an I loading test to assess
I sufficiency of the whole human body.
For the I-loading test to be widely used in the physician’s office, the measurement of urine I levels would be best performed in situ, using a simple method with non-hazardous reagents. The values for I presented in Tables I and II were obtained by a procedure called Induction Coupled Plasma-Mass Spectrometry (ICP-M.S.). The equipment required for this procedure is extremely expensive and very complex in their utilization. The ISE method is very simple, requiring only the following two reagents: water and sodium nitrate. Sodium nitrate is used in the ISE method as an Isotonic Strength Adjuster (ISA) at an initial concentration of 5 Moles/L to improve performance of the ISE electrode. The ISA is diluted 1 part ISA to 2 parts of iodide standards and urine samples. The final concentration of NaNO3 in the assay is 1.66 Molar. The ISE procedure does not require any special precaution, beside the usual good laboratory practice. Water and NaNO3 are used in the ISE measurement and in the chromatographic purification of urine samples on anion-exchange resin, simplifying the procedure.
III. Measurement of iodide in biological fluids by ion-selective electrode: A review of pertinent publications.
In 1983, Cooper and Croxson (19) wrote a “Letter to the Editor”,
published in the Journal of Clinical Chemistry, describing their unsuccessful
attempt to measure urine iodide levels in New Zealanders by the direct ISE
method, using equipment from Thermo Orion,
In 1986, Yabu et al (20) came to the realization that the New Zealander’s problem was not a problem at all for mainland Japanese. Although they confirmed Cooper and Croxson’s findings that the assay was not specific below 1.27 mg/L, mainland Japanese excreted higher levels of urinary iodide than 1.27 mg/L. In 163 urine specimens analyzed, only one specimen had a concentration below 1.27 mg/L. They observed I levels in these urine samples ranging from 0.6 mg/L to 17.4 mg/L. If those I levels are expressed as mg/24 hr. and assuming an average 24hr. urine volume of 1.5 liter, the range of I excretion per 24 hr. would be from 1 to 25 mg in these 163 Japanese subjects. This range is in agreement with the estimated average daily I intake of 13.8 mg I in mainland Japanese (13).
The iodide levels observed in
the mainland Japanese were two orders of magnitude higher than urinary iodide
concentrations in New Zealanders, for that matter, in citizens of the Western
World (13). In 1993, Kono et al (21) using direct measurement of
urine iodide in 2956 men and 1182 women confirmed the reliability of the direct
ion-selective electrode assay in urine samples from mainland Japanese
subjects. However, Yabu
and Kono were not able to measure accurately iodide
levels below 1.27 mg/L, due to chloride interference. Above that level, they achieve excellent
correlation with an established assay for urinary iodide, the ceric ion-arsenious acid method (22). It is of interest to note that the electrode
and meter used in the 2 publications from
In 1980, Lacroix and Wong
measured iodide directly in cow milk by ion selective electrode (23). They reported a value ranging from 0.14 to
0.35 mg/L, when the milk analyzed was taken raw from individual cows. Market milk contained mean levels ranging
from 0.52 to 0.70 mg/L. These authors
did not perform experiments to prove the specificity of their procedure. In 1984, Gushurst
el al (24) measured iodide in
human milk by ion-selective electrode.
They observed values ranging from 0.029 to 0.45 mg/L. Since the concentration of chloride in milk
is 10 times less than in urine (25), they were able to measure
iodide levels down to 0.029 mg/L. The
studies performed with milk samples used iodide-selective electrode and meter
from Thermo Orion,
IV. Purification of urine samples by anion-exchange chromatography prior to assay of iodide
For the ISE method to become widely used in the clinical setting, it must be reliable at all levels of urinary iodide, down to levels observed in severe I deficiency (<0.025 mg/L). To our knowledge, a procedure combining prior chromatographic purification to improve specificity and sensitivity of the ISE assay of iodide in biological fluids has not been published. In our opinion, purification prior to ISE measurement is a sine qua non requirement for specificity and sensitivity of the ISE assay under all physiological and pathological conditions, including severe I deficiency (urine I <0.025 mg/L). Chromatographic purification of urine samples on columns of anion-exchange resin was selected for the reasons described below.
In 1962, Murthy et al (25) reported a procedure for removing radioactive iodide from milk. A strong anion exchange resin was used (Dowex 2 X 8) to retain the radioactive iodide and large volume of milk could be processed through these columns. A mean ± SD of 98 ± 2% of the iodide could be retained on the columns when 120 bed volumes were chromatographed. The bed volume is approximately 1 ml per gm of resin. They were able to elute approximately 98% of the radioactive iodide from the column with 30 bed volumes of 2N sodium nitrate (NaNO3) in 0.16N HNO3. This publication was of great interest to us since the ISE assay of urinary iodide published by the Japanese scientists (20, 21) used 5 ml of 5N NaNO3 as ISA, added to 10 ml of urine. We postulated that by prior chromatographic purification of urine samples on anion exchange resin and using 5N NaNO3 as the elution solvent to elute iodide, measurement of iodide could be made directly after adding 2 volumes of water to the eluant.
Materials used in anion
exchange chromatography are composed of 3 components attached together and
placed in a column: the base or backbone support; the functional group or ion
exchanger, and the counter ion available for exchange. For backbone, styrene divinyl
benzene (SDB) was preferred over silica gel because it is more rugged, less
sensitive to pH changes and possesses a higher capacity (26). For
example, SAX columns with silica backbone are available from Varian and
Strong anion exchangers are quaternary amines versus weak anion exchangers, which are primary, secondary and tertiary amines. Strong anion exchangers are always charged at any pH; therefore elution of the analate of interest could be achieved by increasing the ionic strength of the elution solvent without any acid added. Data are available for strong anion exchangers regarding the relative selectivity of halides (26): With fluoride as unity; chloride has a relative selectivity of 10; bromide 28; and iodide 87. The higher the number, the stronger the binding of the halide to the anion exchanger. The stronger the binding of the halide to the ion exchanger, the higher the ionic strength required for elution. Therefore, by choosing a wash solvent with ionic strength high enough to elute fluoride, chloride and bromine, but not high enough to elute iodide, a high degree of purity of the iodide fraction could be achieved.
For counterions, the choice from products available commercially, was between chloride and acetate. Since chloride interferes in the assay, we chose the acetate form (Fig. 1). Although a wide range of counterions could be prepared by preconditioning the anion exchange columns, this would not be practical in a clinical setting. The ideal counterion on the SAX columns used for the purification of iodide from the other halides would be nitrate. Based on information supplied by Alltech with the SAX columns, iodide is the only halide capable of displacing nitrate from the tetramethylamnonium group. The smaller pore size of 60Ĺ was preferable because it excluded molecules with molecular weight above 1000 and it prevented overloading the resin with high molecular weight anions present in urine samples. Finally, the larger particle size was chosen because it allowed elution at the proper flow rate with lower pressure and vacuum. In Table III are displayed the various options commercially available for anion exchange chromatography. The characteristics chosen are in the right column.
The strong anion exchanger SAX
was obtained from Alltech (
The 500 mg column with a 10 ml reservoir was chosen (Alltech part #309750). Ten ml of urine was applied to the SAX column, which was fixed on top of a vacuum manifold (Applied Separation Inc., Allentown, PA), connected to a vacuum pump (Alltech, Deerfield, Ill). We used the model # Bench Top Vacuum Station which was capable of maintaining a preset vacuum. A vacuum of only 2 inches (50 mm) of mercury was sufficient for an elution flow rate of 4-5 ml/min. Due to variation in airflow through the different openings of the vacuum manifold and variation of elution flow rates between the columns, there was a twofold difference between columns with the fastest and slowest flow rate. The elution of 10 ml of urine required 2 to 4 minutes at the vacuum setting of 50 mm Hg.
The 4 halides, fluoride, chloride, bromide and iodide were added individually in known amounts from stock standard solutions to pooled urine samples collected from a fasting subject. Using Thermo-Orion ISE electrodes and special reagents, the halides were measured following chromatography in the eluted urine, in the wash solvent (10 ml of 0.5N NaNO3) and in the elution solvent (5 ml of 5N NaNO3). The standard curves for the 4 halides are displayed in Fig. 2.
The eluted urine contained fluoride and 75-80% of the
chloride. Some 20-25% of the chloride
was retained on the column, together with bromide and iodide. A wash of the column with 10 ml of 0.5N NaNO3
eluted the retained chloride and the bromide. Quantitative recovery of iodide (>95%) was achieved with 5 ml 5N
NaNO3. The eluant containing the iodide in 5 ml of 5N NaNO3 was
mixed with 10 ml of water and measured directly by immersion of the iodide
selective electrode (Orion Electrode #9653 BN) connected to the Orion Meter
720-A Plus. Standards of potassium
iodide (Spectrum Chemical,
Urine samples collected over a period of 24 hr were stored by the subject during collection in a 3 liter plastic bottle, supplied by Doctor’s Data Inc. After measurement of the total volume at the clinic, sodium azide was added at a final concentration of 0.05% for bacteriostatic purpose (10ml of a 5% solution per liter of urine). Sodium azide is the commonly used bacteriostatic agent in such cases (20). Prior to addition of the sodium azide, a sample was obtained and mailed to Doctor’s Data for analysis by ICP-M.S. Samples of the collected urine were then stored at -20ş C in plastic containers until assayed by the ISE method. Repeated freezing and thawing the urine samples had no significant effect on the measured I levels. However, without a bacteriostatic agent, such manipulation of the samples resulted in decreasing I levels and evidence of bacterial growth. Aqueous solutions of 0.5N and 5N NaNO3 (Spectrum Chemical #SO183) were prepared and stored at room temperature. A stock solution of potassium iodide 1.66 gm in 1 liter of purified water (10-2 Molar) was stored in a dark glass bottle. From this stock solution, iodide standards were prepared by dilution to contain a range from 10-3 M
(127 mg/L) to 10-8 M (0.00127 mg/L).
Under a vacuum of 40 to 50 mm
Hg, 10 ml of urine was applied to a SAX column 500 mg, with a 10 ml reservoir (Alltech #309750) and the elution flow rate adjusted so not
to exceed 4-5 ml/min. This is the most
critical step in the assay. A slower
flow rate did not have an adverse effect on the performance of the
anion-exchange columns. Exceeding this
flow rate however, caused breakthrough of iodide in the urine eluate, with low recovery of iodide in the assay. At the same vacuum setting, the elution flow
rate decreased with the wash and elution solvents. Therefore, it was very important to set the
flow rate during the elution of the urine sample. Since there was variation in flow rate
between the columns, the SAX column with the highest flow rate was used to
monitor visually the urine level in the reservoir. To facilitate this process of observing urine
levels through the opalescent wall of the reservoir, a food coloring was added
to the urine samples prior to chromatography.
FD & C Green No. 3 (Warner Jenkinson
We have tested several SAX columns with both silica and SDB backbones obtained from Alltech and Varian. The vacuum setting required for the proper elution flow rate varied widely between SAX columns with as much as 15 inches (375 mm) Hg for some SAX columns with silica backbone and small particle sizes. With the Alltech 500 mg SAX columns, however, a vacuum setting of
50 mm Hg resulted consistently in the proper flow rate. The Alltech vacuum pump displayed the ambient atmospheric pressure in mm Hg. The desired vacuum was achieved by setting the vacuum pump at 50 mm below ambient.
Chromatography of the urine sample on the SAX column yielded 3 fractions, which were used to measure fluoride, bromide and iodide. The flow chart in Fig. 4 summarized this procedure. The eluted urine contains >95% of the fluoride and 75-80% of chloride. Ten ml of the special ISA TISAB II (Thermo Orion #940909) was added to the 10 ml of eluted urine and fluoride level was measured with electrode #9609BN. The wash solvent consisted of 10 ml of 0.5N NaNO3 and following chromatography on the SAX column contained 20-25% chloride and >95% bromide. Using the electrode #9635BN, bromide levels were measured following addition of 5 ml of 5N NaNO3 to the eluted wash solvent. The bromide standards used to compute the standard curve were prepared in
0.5N NaNO3. Validation of the bromide assay will be the subject of another report. The last step was the addition of 5 ml of 5N NaNO3 to the column and elution of iodide at the same vacuum setting, although the flow rate was less, between 2 to 4 ml/min. Ten ml of water was mixed with the eluted 5 ml 5N NaNO3. Iodide concentration was measured directly by immersion of the electrode (Orion #9653 BN).
VI. Acceptability of the ISE method for urinary iodide measurement
We followed the same procedure we previously described for the validation of radioimmunoassay of steroid hormones in biological fluids (28, 29). The criteria for acceptability of an assay includes reliability and practicability. The reliability of an assay depends on its sensitivity, specificity, accuracy and precision. The practicability of an assay is judged by the skill required to perform it, the time involved in its performance and the cost of the assay.
A) Reliability experiments
The theoretical limit of sensitivity achievable with ISE assay of urinary iodide is set by the sensitivity of the iodide selective electrode itself. From data supplied by Thermo Orion, the sensitivities of the ISE electrodes for halides are: For iodide, 5 x 10-8 M; for fluoride, 10-6 M; for bromide, 5 x 10-6 M; and for chloride, 5 x 10-5 M. The iodide selective electrode is by far the most sensitive being 20 times more sensitive than the ISE electrode for fluoride, 100 time more sensitive than for bromide and 1000 times more sensitive than for chloride. Expressed as mg/L, the iodide selective electrode is sensitive down to 0.006 mg/L, compared to a sensitivity of 0.003 mg/L, for ICP-M.S. used by Doctor’s Data Laboratories. (Information on sensitivity of ICP-M.S. supplied by Dean Bass).
In achieving this theoretical sensitivity, other conditions are important. First, the sensitivity of the standard curve is a limiting factor. The sensitivity of the standard curve is defined as the smallest amount of iodide that is significantly different from zero at the 95% confidence limit. In order to compute the standard curve, (the dose response curve) the EMF expressed in millivolts (mV) was plotted on the Y-axis against the logarithm of increasing amount of iodide, from 10-3 M to 10-8 M on the X-axis. The iodide selective electrode was extremely sensitive (Fig. 5), with a linear response from 10-3 M to 10-7 M. A mean D EMF of 61 mV per decade was observed from 10-3 M to 10-7 M, but from 10-7 M to 10-8 M, the standard curve became non-linear with only 36.2 mV per decade.
To calculate the mean blank value, samples containing zero iodide are run in the assay using several replicates, ideally 6 replicates. The sensitivity would then be equal to 2 standard deviations from the mean blank value, after subtracting the mean blank value. We tested water blanks and deiodized urine blanks. When 6 samples of water of 10 ml each were chromatographed on the SAX column as described under methodology, we obtained a mean ± SD of 0.0024 ± 0.0006 mg/L. Deiodized urine was prepared as described by Cooper and Croxson (19). The 95% confidence limits of the mean blank were: 0.003 - 0.005 mg/L. Based on this information, a sensitivity of 0.005 mg/L could be achieved, a value very close to the 0.006 mg/L suggested by Thermo Orion. This sensitivity however could be improved by threefold, using 30 ml of urine for chromatography, but keeping the wash solvent volume at 10 ml and elution solvent volume at 5 ml. Using 30 ml of urine, the sensitivity in measuring I in urine samples by the ISE method was 0.0017 mg/L, comparable to the sensitivity of ICP-M.S.
There are various ways of validating an assay in terms of its specificity, one of which is by comparison with an accepted method. Yabu et al (19) and Kono et al (20) validated the specificity of the ISE method for direct measurement of urinary iodide levels by comparison with the ceric ion-arsenious acid
method (21). However, their direct assay without prior
purification proved unreliable with urinary I levels below 1.27 mg/L. In our
To validate the specificity of our procedure, we chose the ICP-M.S. as the valid, accepted method. From the data presented in Tables I and II, urine samples were available for comparison from 10 subjects (one sample per subject) for baseline I levels; and urine samples from the 6 subjects in Table II were used for the post-I supplementation comparison of the ISE method with ICP-M.S. Out of 18 samples analyzed by ICP-M.S. in those 6 subjects following I-supplementation; 15 samples were available for comparison with the ICP-M.S. method. With baseline urinary I levels between 0.022 mg/24 hr. to 0.25 mg/24 hr. in the 10 samples used for comparison (Fig. 6), a correlation coefficient of 0.996 (p<0.001) was obtained. For urinary I levels expected in the U.S. population, the ISE method described in this manuscript is therefore a reliable assay and the cost of setting up the ISE procedure is within the reach of the average clinician.
We have not achieved as good
a correlation with ICP-M.S., using urine samples with I levels in the range
observed in mainland Japanese, that is 100 fold higher values. Urinary I levels following 3 tablets of IodoralŇ were consistently higher by the ISE method, being as
much as 65% higher than reported by ICP-M.S.
For example, in sample #13 (Table IV), a value of 11 mg I/24 hr. was
reported by ICP-M.S. following 3 tablets of IodoralŇ. We measured
18.2 mg I/24 hr. in the same sample.
Another sample from the same urine collection was sent to Doctor’s Data,
but labeled as a new sample. The repeat
value was 16 mg I/24 hr. One of us (GEA)
talked to Dean Bass who was very helpful.
He explained that his equipment is calibrated to measure I levels within
the range expected in the
The accuracy of the ISE method was tested by recovery experiments. To deiodized urine was added increasing amount of potassium iodide from 0.01 uM to 100 uM and measurement of I was performed in 5 replicates at each dose level. The recovery experiment was performed in the same batch of samples. The mean percent recovery over the range tested varied from 91% to 112% (Table V).
The within assay variance was tested by performing 5 replicate analysis of 3 urine samples, one sample
with baseline I level; and 2 samples following I supplementation. For the between assay variance, these 3 urine samples were measured on 5 consecutive days. The coefficient of variation was higher for between assay than within assay, with a range of 5.7 to 10.5% for within assay and a range of 10.5 to 18% for between assay precision (Table VI).
As previously mentioned, the practicability of an assay depends on the degree of skill required to perform it, the time involved in its performance and the cost of the assay.
First, we should mention that the Clinical
Laboratory Improvement Amendments of 1988 (CLIA) defined two categories of
complexity for laboratory test: Moderate complexity and high complexity
testing. The ISE method is only 20 years
old and is used currently in University and Research laboratories, and rarely in
clinical laboratories. For example,
Doctor’s Data Inc. performs urinary fluoride levels by the ISE method and it is
classified as high complexity testing mainly because the ISE procedure is not
widely used in the clinical context, at least, not in the
Obviously, familiarity with laboratory equipment such as vacuum manifold, solid phase extraction and potentionmetric measuring devices is a basic requirement for the analyst involved in ISE measurement. Although no special skill is required for implementation of this procedure in a physician’s office, meticulous attention to cleanliness, awareness of the possible sources interference and consistency in the performance of the ISE method are qualities that the technician involved in ISE measurement must have. A clearly written protocol and well defined guidelines of quality control should not be difficult to comply with, mainly in a clinic laboratory already approved for moderate complexity procedures.
2) Time involved
Vacuum manifolds are available from Applied Separations Inc., with 30 positions, so that chromatography of 30 samples could be performed in one batch. The ISE measurement of iodide is relatively rapid, usually less than 5 minutes per sample. This procedure lends itself to automation and equipments are commercially available for this purpose. We have just acquired a new model from Thermo Orion, the #960 Meter with a 45 position Autosampler. This minimizes human intervention and therefore human error. It is of interest to note that using the 960 Model, the sensitivity is calculated by proprietary software in the unit, without human intervention. Surprisingly, the computed sensitivity for I determination, using the same electrode was 0.006 mg/L, the same value we obtained, as described previously with the model 720 A-Plus meter. The upgrade from semiautomation to full automation could be justified with increased number of samples, such as in a Polyclinic or commercial laboratory.
The 720 A Plus meter, with iodide-selective electrode and printer; the 30 position vacuum manifold; the computerized vacuum pump, plus the usual laboratory glassware and pipetting devices, would require an initial investment of $5000.00. We are currently preparing a list of equipments and other items necessary to get started in a physician’s office laboratory already approved by CLIA for moderate complexity testing. Check with local CLIA representative and your clinical pathologist for the requirements.
Since the discovery of
iodine/iodide in the early 1800’s, the measurement of this element has
progressed steadily from colorimetry to the present
mass-spectrometry. In the
The ISE procedure for iodide
is very simple, using non-toxic reagents, and yielding results within
B) Clinical applications
It is estimated that a third of mankind suffers from I deficiency, defined by the World Health Organization as urinary I levels below 0.05 mg/L (1). However, I sufficiency to prevent simple goiter, and cretinism was considered adequate. I sufficiency of the whole human body has never been studied. Based on a review of published studies, we previously proposed that an amount of I about 100 times the RDA would be required for I sufficiency of the whole human body (13, 30). Using this new definition of I sufficiency, only mainland Japanese consume adequate levels of I, with 99% of the world suffering from I deficiency.
There is a great need for a simple test to assess I sufficiency of the whole human body. The I loading test mentioned in this manuscript, using 3 tablets of IodoralŇ, may be adequate in a clinical setting. Correlation of % I retained with clinical improvement of such conditions as FDB could be used to fine tune this I-loading test. Ghent et al (5) have suggested that the amount of I needed in women was dependent on their body weight. The preliminary data presented in this manuscript suggest that breast size and pathology may also play an important role in I requirement by the whole human body.
The high prevalence of I
deficiency in the adult female
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