To establish references for thyroid 24h 123I uptake value (TUV), we reviewed 475 patients who had freeT4 and TSH dosages, and TUV measured 24h after the administration of 123I. The patients were separated in 3 groups: hyperthyroid, euthyroid and hypothyroid, according to thyroid hormone results. The mean and standard deviation (SD) of the TUVs were calculated for each group. We used the unpaired T test to compare the means and ROC curves to evaluate the best TUV to separate the groups. The mean and SD of TUVs for the groups were: hyperthyroid (36.5% ± 16.5%), euthyroid (14.4% ± 5.48%) and hypothyroid (13.7% ± 7.5%). The unpaired T test showed statistically significant difference between hyperthyroid and euthyroid groups (p< 0.01). There was no significative difference between hypothyroid and euthyroid groups (p= 0.55). The 23% TUV has the best sensitivity (80%) / specificity (93%) ratio to separate hyperthyroid from euthyroid groups. There was not a good TUV to separate euthyroid form hypothyroid groups. In conclusion, it can be established 23% as the optimal superior limit for the normal uptake values. However, it was not possible to establish a suitable inferior limit, due to the expressive overlay of TUVs of hypothyroid and euthyroid groups.
Thyroid uptake; Iodine-123; Reference values; T-test; ROC curves
