Systemic immune-inflammation index: A new marker in differentiation of different thyroid diseases.

Inflammation plays an important role in the pathogenesis of many cancer types and is associated with thyroid malignancy. The systemic immune-inflammation index (SII) is a new inflammation marker that can be calculated from routine complete blood count (CBC). This study investigated the association between SII, a marker derived from routine CBC, and different thyroid diseases. The objective was to determine if this simple inflammation marker can distinguish between benign and malignant thyroid diseases. The medical records of all patients who underwent surgical treatment for thyroid disease between January 2018 and January 2022 were systematically evaluated. The routine preoperative CBC parameters' demographic, clinical, and laboratory data were recorded. A total of 241 patients were included in the study, and the patients were grouped as having multinodular goiter (n = 125), lymphocytic thyroiditis (n = 44), and papillary thyroid carcinoma (PTC) (n = 73) according to pathological results. The SII was defined as the ratio of the total count of neutrophils × platelets divided by the lymphocyte count. Subgroup analysis of patients was performed according to the presence of follicular variant or thyroiditis, micro or macro carcinoma, or bilaterality of the tumor. The SII level was significantly higher in the PTC group than in the lymphocytic thyroiditis and multinodular goiter groups (P < .001). When we grouped the patients according to the presence of PTC as benign or malignant, the optimum cutoff point for SII level was found 654.13, with 73.8% sensitivity and 72.3% specificity from ROC analysis. In the subgroup analysis of patients with PTC, the SII level was similar according to the clinicopathological characteristics of the tumor. The differential diagnosis of thyroid diseases is important for patient management. We found that preoperative SII levels were significantly elevated in patients with PTC compared to those with benign thyroid disorders, and this simple marker can be used for the differentiation of benign and malignant thyroid disease.