ObjectiveData on the effects of radioiodine (RAI) therapy on systemic inflammation are very limited. The aim of this study is to explore alterations of subclinical systemic inflammatory markers, such as neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and mean platelet volume (MPV), after RAI therapy in patients with differentiated thyroid carcinoma (DTC).Materials and methodsWe evaluated 57 DTC patients treated with RAI (RAI group), 37 DTC patients not treated with RAI (non-RAI control group), and 37 age-matched healthy individuals (healthy control group). NLR, PLR, and MPV levels were compared among the study groups; these were also examined after RAI in the RAI group.ResultsInitially, NLR was significantly higher in the RAI group than in the healthy controls. NLR and PLR increased significantly and MPV decreased significantly 2 months after RAI therapy (P=0.021, 0.001, and 0.008, respectively). Although NLR and PLR levels decreased, they were still high compared with the preoperative values. MPV returned to normal levels at 6 months. These parameters did not change significantly in the non-RAI control group.ConclusionThis is the first study to evaluate changes in NLR, PLR, and MPV after RAI therapy. Our findings suggest that NLR, PLR, and MPV changes indicate systemic inflammation that occurs after RAI therapy because of thyroid remnant tissue ablation.