JOURNAL OF NUCLEAR MEDICINE 5:828-839, i964 Determination of Protein-Bound Iodine (PB!) In Human Plasma by Thermal Neutron Activation Analysis2

In this communication, we shall attempt to demonstrate that thermal neutron activation analysis is a precise and rapid method for measuring the protein-bound iodine (PBI) concentration in human plasma. In its present form, the procedure is not economically competitive with the chemical methods, but further de velopment, including automation, would make it so. Furthermore, the finding of a systematically higher value by the neutron activation analysis method when compared to the Barker chemical method is consistent with the viewpoint that other PBI compounds, in addition to iodothyronines, may be present normally in plasma. Chemical procedures currently used for determining PBI are technically dif ficult and subject to the problems of contamination from beginning to end. Acland (1) has reviewed the various chemical methods of determining the PB! and has discussed the difficulties associated with each. Kellershohn et al (6) utilized thermal neutron activation analysis to eli minate the colorimetric determination of iodine as a final step in the chemica