Determination of the Thyroxine Iodine Content of Serum Contaminated by Organic Iodines. A Method Based on Gel Filtration12

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Abstract
A new method employing Sephadex G-25 gel filtration for the separation of various iodinated radiographic contrast agents from thyroxine (T4) in serum is described. Since T4 is split from serum binding proteins on the alkaline gel columns, no prehandling or extractions of serum are required. The contaminating iodinated substances are eluted from the columns with Tris-HCl, and T4 is only later eluted with a 2N NH4OH eluent. PBI and serum T4 iodine content (T4IC) determinations in 60 euthyroid, 16 hyper thyroid and 8 hypothyroid individuals were as follows: euthyroid—PBI 6.9 ± 1.2 (sd), T4IC 6.2 ± 1.3 μg/100 ml; hyperthyroid—PBI 16.2 ±3.7, T4IC 13.7 ±2.8 μg/100 ml; hypothyroid —PBI 3.0 ±0.7, T4IC 2.5 ±0.8 μg/100 ml. Results of T4IC determinations on serum obtained from several patients before and shortly after x-ray studies employing the administration of Hypaque, Pantopaque, Cholografin and Telepaque have shown statistically identical results (p > 0.2), attesting to the effective separation of these iodinated contaminants from T4 by this method. In addition, preliminary experiments in which Gastrografin, Dionosil, Lipiodol and Ethiodal have been added to serum in vitro have demonstrated the effective separation of these agents from T4. The method is simple, rapid, and the recoveries are sufficiently high and reproducible to obviate the need of an 131I-T4 tracer to correct for recovery.

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