Standardization of reference values for thyroid uptake using I-123

Purpose: To establish new normal ranges for thyroid uptake after 2, 6 and 24 hours,using 123I. Methods: The author reviewed data of 316 patients in a Nuclear Medicine laboratory whose free T4 and TSH values were within the normal range; and the thyroid uptake 2, 6, and 24 hours after 123I administration. Results: the results were statistically analyzed using the Kolmogorov-Smirnov test, asymmetry and kurtosis, and appear to belong to a gaussian distribution; therefore, the reference interval was built considering it. The author also performed the unpaired t test in order to compare means and variances in both sexes. The results showed p = 0.2039 for mean testing and p = 0.0716 for variance testing, meaning that the differences between these two parameters in both sexes were not statistically significant. Three new normal ranges were established: 2-hour uptake, 0 to 8%; 6-hour uptake, 0 to 16% and, 24-hour uptake, 3 to 23%. Conclusions: The author concluded that the thyroid uptake normal range must be periodically established for each individual laboratory; specially when there is any kind of change in thyroid uptake technology