Evaluation of three inflammation-associated blood indices for predicting malignancy in thyroid nodules

Differentiated thyroid carcinoma (DTC) is the most common endocrine malignancy and usually has a favorable prognosis. However, both diagnostic and prognostic evaluations currently rely mainly on postoperative histopathological results. Systemic inflammation-based indices - such as the Systemic Immune-Inflammation Index (SII), Systemic Inflammation Response Index (SIRI), and Pan-Immune Inflammation Value (PIV) - have recently emerged as potential biomarkers in various cancers. This study aimed to evaluate the diagnostic and prognostic utility of these indices in patients undergoing thyroid surgery.

This retrospective study included 554 patients who underwent total thyroidectomy between 2014 and 2021. Tumors were categorized as benign or malignant according to final histopathology. SII, SIRI, and PIV were calculated from preoperative complete blood counts. Multivariate logistic regression was performed and included age, sex, thyroid-stimulating hormone (TSH) level, glycated hemoglobin (HbA1c) level, and diabetes status. Receiver operating characteristic (ROC) analysis was used to determine diagnostic performance.

Among 554 patients, 366 had benign and 188 had malignant tumors. Among the systemic inflammatory markers, only the SII differed significantly between groups (p = 0.002) and remained an independent predictor of malignancy in multivariate analysis (OR = 0.85 per 100-unit increase, p = 0.007). ROC analysis revealed an AUC of 0.597, with 65.8% sensitivity and 58.2% specificity. None of the indices demonstrated prognostic value in the subgroup analyses.

The SII demonstrated independent but clinically limited diagnostic value in differentiating malignant from benign thyroid lesions. Although its accuracy was poor (AUC <0.6), the SII may serve as a low-cost adjunct within multivariable preoperative models, particularly in indeterminate cytology cases.