Evaluation of early (5 to 6 hours) iodine 123 uptake for diagnosis and treatment planning in Graves' disease.
BACKGROUND
Twenty-four-hour radioactive iodine uptake measurements necessitate extra visits and time delays in diagnostic confirmation of and therapy planning for hyperthyroid patients. We evaluated the early (5 to 6 hours) measurement of iodine 123 uptake (EU) to predict late (24 hours) uptake (LU) and assessed its value in the management of hyperthyroidism.


METHODS
We conducted a prospective study in 51 previously untreated hyperthyroid and 27 euthyroid patients (initial evaluation group). Patients underwent both 6- and 24-hour 123I uptake measurements. A subsequent 21 patients with Graves' disease (confirmation group) were evaluated in light of regression data generated in the initial evaluation group.


RESULTS
An EU value of greater than 20% had a sensitivity of 100%, a specificity of 96%, and a positive predictive value of 98% for the diagnosis of hyperthyroidism and was superior to the most predictive LU value (> 30%), which had a sensitivity of 98%, a specificity of 89%, and a positive predictive value of 94%, in distinguishing the hyperthyroid patients from euthyroid patients or those with subacute thyroiditis. Regression analysis revealed that the 24-hour uptake of the hyperthyroid patients could be predicted from the early measurement with the following formula: LU = 28.94 + 0.584 (EU). The measured EU of the confirmation group was used to calculate a predicted LU with use of this formula. Measured LU and predicted LU correlated well (r = .85, P < .001). Iodine 131 dose calculations were performed post hoc; LU calculated doses correlated with predicted LU doses (r = .91, P < .001). Mean dose differences were small.


CONCLUSIONS
The EU of 123I can replace 24-hour uptake measurements. Early uptake measurement is reliable and clinically useful for diagnosis confirmation and treatment planning in thyrotoxic patients.
Hennessey
J V
JV
Department of Medicine, Wright State University School of Medicine, Dayton, Ohio.
Berg
L A
LA
Ibrahim
M A
MA
Markert
R J
RJ
D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006111:Graves Disease / Q000175:diagnosis* / Q000378:metabolism / Q000628:therapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism* / Q000627:therapeutic use; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors
D007457:Iodine Radioisotopes