Simplified Technic for the Determination of Serum Protein-Bound Iodine

A simplified technic for the determination of serum protein-bound iodine (PBI) is presented. Endogenouslylabeled 1131 PBI is completely recovered. The technic is basedon the method of Barker et al. (1) and includes the following modifications: The number of washesof the precipitated serum proteins are decreased. Unashed iodide standards are used in a sodium carbonate solution rather than an internal standard. A temperature-correction formula is employed to allow the ceric-arsenite-iodide reaction to be carried out at room temperature, and a stable cerate color is producedwith brucine sulfate so that the colorimetry is carried out with greater convenience. The serum PBI concentrations are read directly from a graph, which simplifies the calculations. INTEREST in the technic of determining serum protein-bound iodine (PBI) has continued to increase since this test was recognized as a valuable tool in the diagnosis and management of thyroid disease. Although most of the commonly employed methods for this deter-mination are considered to be accurate and reproducible, they are not completely satisfactory for busy clinical and research labora-tories because they are time consuming and require constant atten-tion by the analyst. In this laboratory, several published methods were tried. The method of Barker et at. (1) employed the internal standard which not only limited the number of samples that could be completed at one time, but involved tedious calculations. Grossman and Grossman (2) presented a method for the production of a stable cerate color with brucine sulfate. Their modification increased the number o