Differentiated thyroid cancer (DTC) is the most common type of thyroid cancer, and a proportion of patients may still develop metastasis despite undergoing radioactive iodine (RAI) ablation with I-131. Systemic inflammatory biomarkers such as the neutrophil-to-lymphocyte ratio (NLR) have gained increasing attention due to their potential in predicting cancer progression and metastasis. However, evidence regarding their role in post-RAI DTC patients remains limited. This study aims to evaluate the ability of NLR as an inflammatory biomarker for predicting metastasis in patients with DTC after I-131 radioiodine ablation.

This retrospective study analyzed medical record data from DTC patients who underwent total thyroidectomy and received I-131 RAI therapy at Hasan Sadikin General Hospital Bandung, and were evaluated 6 to 9 months after the initial treatment between May and November 2025. A total of 28 patients were included, comprising of 8 metastatic and 20 non-metastatic cases. Statistical analyses included the Mann–Whitney test to compare NLR values between groups, and receiver operating characteristic (ROC) curve analysis to determine diagnostic accuracy, sensitivity, specificity, and the optimal cut-off value for predicting metastasis.

A significant difference in NLR values was observed between metastatic and non-metastatic patients (p = 0.005). ROC analysis yielded an area under the curve (AUC) of 83.8%, reflecting good predictive performance.. The optimal NLR cut-off value was 2.32, corresponding to a sensitivity of 87.5% and a specificity of 70% for predicting metastatic.

NLR demonstrates promising potential as an accessible and practical inflammatory biomarker for predicting metastasis in DTC patients following I-131 radioiodine ablation. These findings support the use of NLR as a simple and cost-effective adjunct in the early assessment of metastatic risk among DTC patients.