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systemic immune-inflammation index

systemic immune-inflammation index

Overview

The systemic immune-inflammation index (SII) is a blood-derived inflammatory index used in clinical and translational research to summarize systemic immune and inflammatory status from routine laboratory data. It is typically calculated from peripheral blood cell counts and is commonly discussed alongside related composite markers such as the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), lymphocyte-to-monocyte ratio, and the pan-immune-inflammation value (PIV). Because it integrates information from neutrophils, lymphocytes, and platelets, SII is often interpreted as a marker of inflammatory activation and immune dysregulation.

In recent biomedical studies, SII has been investigated as a potential indicator of disease activity, prognosis, and functional outcome across a range of inflammatory and cerebrovascular conditions, including rheumatoid arthritis, gout, psoriatic arthritis, acute cerebral venous thrombosis, post-stroke cognitive impairment, and colorectal cancer surgery recovery. Its appeal lies in its accessibility: it can be derived from a complete blood count, making it practical for repeated measurement and longitudinal monitoring.

Focus of Latest Publications

Recent publications have used SII as a comparative or predictive biomarker in several disease settings.

In psoriatic arthritis, a retrospective cohort study reported that blood-derived inflammatory indices, including NLR, MLR, PLR, SII, PIV, and the CALLY index, were calculated using routine laboratory data. In this context, SII was part of a broader panel of immune-inflammatory markers used to assess inflammatory burden and compare with other indices.

In colorectal cancer surgery, a preliminary inflammatory benchmarks study examined postoperative dynamics of inflammatory markers in patients with uncomplicated recovery. The authors noted that elevated NLR, PLR, and SII pre- or postoperatively have been associated with adverse events such as anastomotic leakage and poor survival, while the normal temporal trajectories of these markers in uncomplicated cases remain insufficiently defined. This places SII in the context of postoperative monitoring and interpretation of inflammatory recovery patterns.

In post-stroke cognitive impairment, a retrospective clinical study found that NIHSS and SII were significantly associated with early peripheral blood inflammatory markers and early post-stroke cognitive impairment. This suggests that SII may contribute to risk stratification in neurological outcomes after stroke, alongside established clinical severity measures such as the NIHSS Score.

In acute cerebral venous thrombosis, the CLOT-VENUS substudy evaluated inflammatory serum biomarkers including NLR, MLR, PLR, and SII, noting that these markers are associated with outcomes in acute cerebrovascular diseases. Here, SII was used as part of a biomarker panel to explore inflammatory correlates of functional outcome.

In atrial fibrillation recurrence, a retrospective cohort study focused on the CALLY index and compared its predictive value with traditional immune-inflammatory markers, including SII, platelet/high-density lipoprotein ratio, and neutrophil/high-density lipoprotein ratio. In this setting, SII served as a benchmark inflammatory index against which a newer composite marker was evaluated.

In hemodialysis patients with end-stage renal disease, a diagnostic utility study assessed systemic inflammatory indices, including NLR, SII, systemic inflammation response index (SIRI), and PIV, for acute cholecystitis. This indicates that SII is being explored as a diagnostic adjunct in complex medically ill populations where inflammation may be difficult to interpret clinically.

In elderly rheumatoid arthritis, an NHANES-based analysis examined the relationship between geriatric nutritional risk index (GNRI) and immune-inflammatory biomarkers, including NPAR, NLR, PLR, LMR, and SII. This study situates SII within the intersection of nutrition, chronic inflammation, and rheumatoid arthritis.

In gout, a longitudinal real-world repeated-measures study reported that SII is associated with flare-related and intercritical inflammatory activity. The study aimed to evaluate within-patient dynamics of systemic inflammatory activation and whether inflammation persists beyond clinically apparent gout flares, suggesting that SII may reflect ongoing inflammatory activity even when symptoms are not overtly present.

In cognitive impairment, another cross-sectional study found that lymphocyte count and SII were associated with cognitive impairment, with binary logistic regression identifying SII as a risk factor. This supports the use of SII as a systemic inflammatory marker potentially linked to neurocognitive outcomes.

Across these studies, SII is consistently presented as a practical, blood-based index that may reflect inflammatory burden and help characterize disease activity, prognosis, or diagnostic likelihood. However, the provided studies are observational and biomarker-focused; they do not establish SII as a causal factor or therapeutic target.

Key Publications

  • Jun Lower CALLY index values are associated with higher disease activity in psoriatic arthritis: a retrospective cohort study. (Rheumatology international, 2026, PMID 42377589): "Blood-derived inflammatory indices, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), pan-immune inflammation value (PIV), and the CALLY index, were calculated using routine laboratory data."
  • Jun Postoperative dynamics of inflammatory markers in patients with uncomplicated recovery after colorectal cancer surgery: a preliminary inflammatory benchmarks study. (Scientific reports, 2026, PMID 42366215): "While elevated NLR, PLR, and SII pre- or postoperatively predict adverse events like anastomotic leakage and poor survival, their normal temporal trajectories in uncomplicated cases remain poorly defined, hindering clinical interpretation."
  • Jun Association between early peripheral blood inflammatory markers and early post-stroke cognitive impairment: a retrospective clinical study. (Neuroscience, 2026, PMID 42002069): "Multivariate logistic regression analysis showed that NIHSS and SII were significantly associated with PSCI."
  • Jun Early Inflammatory Biomarkers Associated With Functional Outcomes in Acute Cerebral Venous Thrombosis: CLOT-VENUS Substudy. (Stroke, 2026, PMID 42017277): "Inflammatory serum biomarkers, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII), are associated with outcomes in acute cerebrovascular diseases."
  • May Association between C-reactive protein-albumin-lymphocyte (CALLY) index and atrial fibrillation recurrence: A retrospective cohort study. (Medicine, 2026, PMID 42175397): "Receiver operating characteristic curves were generated to compare the predictive value of the CALLY index with traditional immune-inflammatory markers: the Systemic Immune-Inflammation Index, platelet/high-density lipoprotein ratio, and neutrophil/high-density lipoprotein ratio."
  • May Diagnostic utility of systemic inflammatory markers for acute cholecystitis in hemodialysis patients with end-stage renal disease. (Medicine, 2026, PMID 42175491): "Systemic inflammatory indices, including the neutrophil-to-lymphocyte ratio, systemic immune-inflammation index, systemic inflammation response index (SIRI), and pan-immune-inflammation value (PIV), were calculated."
  • May The association between geriatric nutritional risk index (GNRI) and immune-inflammatory biomarkers in elderly rheumatoid arthritis: Insights based on NHANES 2005-2018. (Medicine, 2026, PMID 42175440): "This study aimed to explore the relationship between geriatric nutritional risk index (GNRI) and immune-inflammatory biomarkers neutrophil-percentage-to-lymphocyte ratio (NPAR)/neutrophil-to-lymphocyte ratio (NLR)/platelet-to-lymphocyte ratio (PLR)/lymphocyte-to-monocyte ratio (LMR)/systemic immune-inflammation index (SII) in elderly RA patients."
  • May Systemic Immune-Inflammation Index is associated with flare-related and intercritical inflammatory activity in gout: a longitudinal real-world repeated-measures study. (Rheumatology international, 2026, PMID 42154066): "We aimed to evaluate longitudinal within-patient dynamics of systemic inflammatory activation and to determine whether inflammation persists beyond clinically apparent flares and may not always reflect contemporaneous SUA."
  • May Lymphocyte count and systemic immune-inflammation index (SII) as novel biomarkers for cognitive impairment: A cross-sectional study analysis. (Medicine, 2026, PMID 42065191): "Binary logistic regression identified SII as a risk factor (OR: 1.008, 95% CI: 1.003-1.012, P=0.002)."
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