Prediction of late (24-hour) radioactive iodine uptake using early (3-hour) uptake values in Japanese patients with Graves' disease.

Measurement of 24-hour radioactive iodine uptake (RAIU), which is commonly used to calculate the dose of radioiodine (RI) therapy, cannot be accomplished in a single day. The purpose of this study was to predict 24-hour RAIU from 3-hour RAIU in Japanese patients with Graves' disease, and to investigate other factors that could be used to predict 24-hour RAIU. A total of 66 Japanese patients (14 men and 52 women; age, 17-83 years) with Graves' disease who had undergone both 3-hour and 24-hour ¹²³I RAIU measurements between January 2006 and September 2011 were included in this study. Stepwise multiple regression analyses were performed in order to identify factors that could be used to predict 24-hour RAIU. The investigated factors were gender, age, thyroid volume, TSH, free thyroxine (FT4), free triiodothyronine (FT3), serum creatinine, second generation assay TSH receptor antibody (TRAb2), antithyroid drugs discontinuation period (ADP), iodine restriction period and 3-hour RAIU. The ADP was converted to an ordinal scale ADP score (ADPS) for multiple regression analyses. Multiple regression analyses showed that 3-hour RAIU (P < 0.001), FT3 (P < 0.001) and ADPS (P < 0.001) were statistically significant predictive factors of 24-hour RAIU. The relationship between 24-hour RAIU (LU) and 3-hour RAIU (EU), FT3 and ADPS was: LU = 11.5 + 29.1 × log₁₀ EU + 23.0 × log₁₀ FT3 - 2.7 × ADPS (r = 0.82, P < 0.001). The present results indicate that prediction of LU from EU, FT3 and ADPS is feasible in Japanese patients with Graves' disease.