A clinical study in the changes of I-131 thyroid uptake in fasting and non-fasting state

The thyroid radioiodine uptake test, the most widely employed method of evaluating thyroid function, isusually performed as a rule by giving an oral dose of I-131 in fasting stage. Therefore, most of the out-patientshave to visit the hospital infasting state some other day for the uptake study, and it is frequently needed fo thein-patient to stay in hospital one more day so as to get the examination done. For the purpose of reducing such aninconvenience for the patient, the authors have undertaken an observation to evaluate the validity of performingthyroid iodine uptake test in non-fasting condition. The thyroid uptake rates of I-131 were measured in usualmanner after giving an oral dose of 50micro Ci of Na I-131 to 8 healthy individuals infasting and non-fastingstates respectively, and 20-minute uptake curves were recorded at the body surface over the thyroid gland emplyingrenogram apparatus. On the other hand, the plasma level of TSH was titrated by means of radioimmunoassay atfasting state in 22 healthy persons and shortly after meal in 17 individuals. The thyroid uptake of I-131 wasslightly but definitely greater when the examination was performed in non-fasting state than when it was doneinfasting state. The mean values obtained in fasting condition were 6.1±4.1% at 1 hour, 11.5±6.0% at 2 hours,15.3±6.3% at 6 hours and 22.9±5.8% at 24 hours. When the examination was carried out after meal, the mean valueswere 10.0±4.4% at 1 hour, 15.5±4.9% at 2 hours, 22.8±4.2% at 6 hours and 30.4±7.8% aat 24 hours. The earlythyroid uptake curves revealed rapid rising figure several minutes after ingestion of radioiodine in non-fastingstate, while in fasting state definite rising tendency was observed 10 minutes after administration of I-131. Theman values of TSH in the plasma were 1.75±0.64microU/ml. infasting state and 0.70±0.13microU/ml.in non-fastingstate. In conclusion, the thyroid radioiodine uptake test can be done in nono-fasting state with littleinterference in accuracy, so that inconvenience of performing the uptake study in fasting state may be avoided.