THE DETERMINATION OF THYROIDAL AND RENAL PLASMA I131 CLEARANCE RATES AS A ROUTINE DIAGNOSTIC TEST OF THYROID DYSFUNCTION 12

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Abstract
The average space of I131 distr. during the first half hour following its intraven. injn. as KI to nonedematous human subjects is equal to 20% of body weight with a range of [plus or minus] 10% of the mean. From measurements of thyroid uptake in renal excretion of the isotope during this time period, therefore, thyroidal and renal plasma I131 clearance rates may be approximated with fair accuracy. From a theoretical consideration of clearance function and the analysis of plasma concentration-time curves, the following empirical formula for the calculation of thyroid clearance in ml. per min. was derived:[image] where Th and U are the 1/2 hr. thyroid uptake and renal excretion of I131 respectively and Do is the dose administered. Thyroid clearance studies in 87 euthyroid, 18 hyperthyroid and 5 hypothyroid subjects revealed a clearcut differentiation without overlapping between the euthyroid and hyperthyroid cases. 24 hour uptake studies are presented with the criticism that they reflect only the relative abilities of thyroid and kidneys to clear the blood of radioactive iodine while the clearance studies permit evaluation of the absolute level of this thyroid function.