Can the Systemic Immune-Inflammation Index help diagnose Thyroid Cancer?
The Systemic Immune-Inflammation Index (SII) is a simple blood test marker calculated from routine complete blood count (CBC) results. It combines neutrophil, platelet, and lymphocyte counts into a single number. Research suggests SII may help distinguish thyroid cancer from benign thyroid conditions and predict disease severity. However, it is not a standalone diagnostic tool and should be used alongside other tests.
What the research says
A 2025 systematic review and meta-analysis of 10 studies found that SII has moderate diagnostic accuracy for thyroid cancer, with a pooled sensitivity of 76.8% and specificity of 71.2%, and an area under the curve (AUC) of 0.805 2. This means SII correctly identifies about 77% of people with thyroid cancer and correctly rules out about 71% of those without it. The same analysis showed that higher SII levels are significantly associated with lymph node metastasis, a marker of more advanced disease 2.
A 2022 study of 93 patients with differentiated thyroid cancer (DTC) found that SII values were significantly higher in patients than in 33 healthy controls 7. However, SII did not differ based on tumor type, invasion, or extrathyroidal extension, except that it was higher in patients with multiple tumor foci (multifocality) 7.
A 2023 study of 241 patients compared SII across different thyroid conditions: multinodular goiter, lymphocytic thyroiditis, and papillary thyroid carcinoma (PTC). SII was significantly higher in the PTC group than in the benign groups, suggesting it may help differentiate malignant from benign thyroid disease 8.
Additionally, a 2024 study of 406 patients with DTC found that higher SII levels before radioactive iodine therapy predicted a poorer response to treatment, indicating SII may also have prognostic value 6.
What to ask your doctor
- What is my SII value based on my recent blood work, and what does it suggest about my thyroid condition?
- Should SII be used alongside other tests like ultrasound or biopsy to diagnose thyroid cancer?
- If my SII is elevated, does that increase the chance that my thyroid nodule is cancerous?
- Can SII help predict whether my thyroid cancer might spread to lymph nodes?
- How often should SII be monitored if I have a thyroid nodule or a history of thyroid cancer?
This question is drawn from common patient questions about Oncology and answered using cited medical research. We do not provide individualized advice.