Analysis of the Correlation between the Radioactive Iodine Activity and Neutrophil-to-Lymphocyte Ratio in Patients with Differentiated Thyroid Cancer.

Publications investigating the effect of radioactive iodine ( 131 I) therapy on the circulating peripheral blood cells in patients with differentiated thyroid cancer (DTC) are limited to blood samples collected more than 92 h after 131 I. Studies conducted on blood samples collected up to 92 h are rare due to the radioactive contamination risk. This research aimed to assess the relationship between the prescribed 131 I activity, human whole blood activity, and peripheral blood cells at many time points (6, 22, 46, 69, and 92 h after 131 I). The study enrolled 50 female patients with DTC who received a 131 I median activity of 90.54 mCi (3.35 GBq). The neutrophil-to-lymphocyte ratio (NLR) was measured as an inflammatory marker. 131 I uptake in the residual thyroid tissue peaked after 46 h. Blood activity decreased in the first 46 h and increased 69 h after the 131 I intake. Blood activity was associated with the absolute lymphocyte count and the NLR at 69 h (r = -0.49 and r = 0.52, p < 0.001). Our results demonstrate that the time interval between 46 and 69 h should be associated with the release of hematological inflammatory mediators, such as neutrophils and lymphocytes, to eradicate tumor cells in response to 131 I therapy.