Use of Thyroid Hormone to Differentiate Between Hyperthyroidism and Euthyroidism

Shortly after radioactive iodine (I¹³¹) was made available for general use, enthusiastic reports appeared as to its efficacy as a diagnostic agent. Skanse,¹using the 24 hour urinary excretion of the isotope, reported that 98% of the hyperthyroid patients and not one of the euthyroid subjects had diagnostically low excretions. In his series of mildly hyperthyroid patients, the radioactive iodine test was 95% diagnostic as compared to an 86% accuracy of the serum protein-bound iodine determination and a 51% accuracy of the basal metabolic rate determination. Similar findings were reported by Jaffe and Ottoman²who evaluated the 24 hour thyroid accumulation of I¹³¹rather than its excretion in the urine. They observed that the radioactive iodine uptake was 95% accurate as compared with an accuracy of 80% for the serum protein-bound iodine test and of 67% for the basal metabolic rate. Thus of these three diagnostic