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Rapid Urinary Iodide Test

Clinic of Nuclear Medicine (J.R., D.B., C.R.), University of Würzburg, D-97080 Würzburg, Germany; and Merck KGaA (T.G.), D-64271 Darmstadt, Germany

Address all correspondence and requests for reprints to: Dr. Johann Rendl, Clinic of Nuclear Medicine, University of Wuerzburg, Josef-Schneider-Straße 2, D-97080 Wuerzburg, Germany. E-mail: rendl{at}nuklearmedizin.uni-wuerzburg.de

Assessment of iodine deficiency and monitoring of iodine supplementation programs demand rapid, simple, and cost-effective methods for the determination of urinary iodide concentrations. We propose a semiquantitative rapid test, based on the iodide-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine by peracetic acid/H₂O₂, to yield colored products. The color of the chemical reaction is compared with color categories of a pictogram corresponding to three ranges: <100, 100–300, and >300 µg/L (<0.79, 0.79–2.36, and >2.36 µmol/L) of iodide concentrations. The test is very easy to perform and does not require any instrumentation or apparatus. Sample preparation is simple and consists of the removal of interfering substances by disposable columns, 65 x 10.5 mm, packed with purified activated charcoal. For comparison with a reference method for measuring urinary iodide, by high-performance liquid chromatography, we determined the iodide concentrations of 370 random (untimed) urine samples from consecutive patients by both high-performance liquid chromatography and the rapid test. The results obtained by both methods are in close agreement, with respect to classification of the samples according to the above three ranges, with a maximum difference of less than 5% for each range. Median (y) values of a given distribution of urinary iodide concentrations can be calculated from the percent (x) of samples below 100 µg/L (0.79 µmol/L) using the regression equation: y = 179.78 - 1.60x. This rapid test, therefore, is suited to epidemiological surveys of iodine deficiency, especially in developing countries.

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