Can the systemic immune-inflammation index be used as a novel diagnostic tool in the diagnosis of subacute thyroiditis?

Aim: To evaluate systemic inflammatory parameters derived from hematological parameters in the diagnosis and prognosis of subacute thyroiditis (SAT). Methods: Demographic and laboratory data of 170 patients with SAT and 91 healthy control subjects were analysed retrospectively. The authors compared inflammatory parameters and thyroid function tests between SAT and control groups. Results: The erythrocyte sedimentation rate, neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio and systemic immune-inflammatory index (SII) were significantly higher in patients with SAT (p < 0.001). There was a significant positive correlation between the SII and erythrocyte sedimentation rate (r: 0.448; p < 0.001), CRP (r: 0.449; p < 0.01), neutrophil-to-lymphocyte ratio (r: 0.861; p < 0.001) and platelet-to-lymphocyte ratio (r: 0.782, p < 0.001). The thyroid stimulating hormone levels were higher in patients with recurrence when compared with those without recurrence (p = 0.007). Conclusions: As a practical biomarker, SII was significantly higher in patients with SAT compared with the control group. SII may be a new diagnostic tool for SAT.