Differentiated Thyroid Cancer (DTC) is the most common thyroid malignancy and is generally managed with total thyroidectomy followed by radioactive iodine (RAI-131) ablation. The response to the initial ablation is a key determinant of long-term disease control, but clinical outcomes vary among patients. The Neutrophil-to-Lymphocyte Ratio (NLR), a marker of systemic inflammation, has been proposed as a factor contributing to this variability, as elevated NLR may reflect an inflammatory environment that reduces sensitivity to RAI-131. This study aims to evaluate the clinical utility of NLR as a predictor of therapeutic response to RAI-131 in patients with DTC.

This retrospective study included 28 patients with differentiated thyroid cancer in Department of Nuclear Medicine and Theranostic Molecular - Dr. Hasan Sadikin General Hospital Bandung who underwent total thyroidectomy, followed by initial RAI-131 therapy, and were evaluated again 6 to 9 months after the initial treatment, between May and November 2025. Patients were classified into an excellent response (ER) group or a non-excellent response (non-ER) group based on imaging findings and biochemical markers. The Neutrophil-to-Lymphocyte Ratio (NLR) was derived from peripheral blood counts prior to follow up after therapy. The Mann–Whitney test was used to determine whether NLR differed significantly between responders and non-responders. Receiver operating characteristic (ROC) analysis and the corresponding area under the curve (AUC) were employed to assess the predictive performance of NLR for treatment response.

Patients in the non-ER group exhibited significantly higher Neutrophil-to-Lymphocyte Ratios compared with those in the ER group (p = 0.001). ROC analysis identified an optimal NLR cutoff value of 2.32 for predicting treatment response, with an AUC of 0.930, sensitivity of 70.6%, and specificity of 90.9%.

The Neutrophil-to-Lymphocyte Ratio appears to be a promising predictor of response to RAI-131 therapy in patients with differentiated thyroid cancer.