AN APPRAISAL OF THE RADIOIODINE TRACER TECHNIC AS A CLINICAL PROCEDURE IN THE DIAGNOSIS OF THYROID DISORDERS

Abstract

Data from about 1400 tracer tests of thyroid function were analyzed. Uptake of radioiodine, I131, was measured directly over the gland 24 hrs. after ingestion of a tracer dose of 40 microcuries. A comparison of various tracer methods was made from the standpoint of clinical usefulness in terms of simplicity, rapidity and accuracy. The 24-hr. uptake technic seemed most suitable for routine diagnostic and range-finding purposes. The limitations of tracer dosage and of repetition of dosage were discussed. A range of normal uptake of 10-40% at 24 hrs. was established and includes 90% of all euthyroid individuals. A small, but significant, overlap with hyperthyroid and hypothyroid subjects was observed. The sources of error in tracer technics, such as preceding admn. of inorganic and organic compounds containing iodine, or thyroid extract, are reviewed. A limited comparison between the results from the tracer technic and those from the serum precipitable iodine and BMR detns. was made. It is concluded that the use of 2 or more such tests results in a high degree of accuracy of diagnosis (95%, approx.) but still admits the definite possibility of error. Anterior pituitary thyrotropin (T. S. H.) admn. was investigated as a method for differentiation between primary hypothyroidism and hypopituitarism. It appears to be a useful tool. It is stressed that the measurement of a single function of the thyroid, no matter how precise, is not completely reliable as an index of the state of thyroid activity. It is stressed that erroneous conclusions may be drawn even when several functions of the gland are tested. Sound clinical judgment is still the final arbiter in the diagnosis of thyroid disease.