Objective This study aims to systematically evaluate the predictive value of platelet parameters (PLT, PDW, MPV, PCT) before initial 131 I therapy in patients with differentiated thyroid cancer. Methods This retrospective study included 365 patients with differentiated thyroid cancer (DTC) who underwent initial 131 I therapy at the Department of Nuclear Medicine in a tertiary hospital. Treatment response was assessed according to the 2025 American Thyroid Association Guidelines for the Managemen