Blood Levels of 1-131 after Tracer Doses in the Diagnosis of Hyperthyroidism

Summary

By prolonging the study of blood levels after tracer doses of 1-131 to 96 hours we have been able to measure secretion of thyroid hormone into the circulation rather than concentration and fixation by the thyroid gland. This appears to be the best method presently available for clinical use in the diagnosis of hyperthyroidism. A single blood or plasma sample of one cubic centimeter gives diagnostic values when counted after air drying. The determination of the protein-bound fraction only very rarely gives additional information but can be used to exclude spurious high levels as are occasionally found in cases of renal insufficiency where excretion of the circulating inorganic 1-131 is delayed.