Automated measurement of urinary iodine with use of ultraviolet irradiation

Abstract

We have modified an automated measurement system of urinary iodine (UI) and established a sensitive UI assay system by using ultraviolet (UV) digestion. The automated system is sensitive enough to detect concentrations of UI <0.78 μmol/L (<10 μg/dL) in a small volume of urine (500 μL). Sample throughput is >30/h, including a water washing. The within-assay imprecision (CV) was ≤10% in the UI range of 0.10-3.00 μmol/L; the between-assay CV was usually ≤15% in the same range. Analytical recovery of iodine added to urine samples was consistently >90%. The theoretical values were recovered when UV irradiation was used but not in its absence. High (supraphysiological) doses of thiocyanate or ascorbic acid, which are major interfering substances to the ceric-arsenious acid reaction, did not interfere with this system. The correlation between UI determined by this method and by the acid digestion method was linear (r = 0.994). For samples containing iodine at <1.00 μmol/L, the correlation between values by both methods was still significant (r = 0.937). UI in an iodine-deficient area in Ukraine, measured by this system, ranged from 0.06 to 1.83 μmol/L (median 0.44 μmol/L, n = 95), significantly lower than in Japan (range 0.23-50.70 μmol/L, median 4.70 μmol/L, n = 84) and consistent with mild iodine deficiency. This modified automated assay system, therefore, is useful and applicable for screening UI in inhabitants of iodine-deficient areas.