Systemic Immune-Inflamation Index and Mortality in ICU Patients

The Relationship Between Systematic Inflammatory Index (SII) and Mortality in Patients Admitted to the Non-Interventional Clinical Research Ethics Committee for Evalation

Systemic Immune-Inflammation Index (SII) is a hemogram-derived biomarker reflecting the balance between systemic inflammation and immune response. In critically ill patients, inflammatory burden at admission may play a key role in prognosis. This retrospective cohort study aims to evaluate the association between admission SII levels and intensive care unit (ICU) mortality in adult patients admitted to a reanimation ICU. Secondary objectives include comparison of mortality according to infectious versus non-infectious admission diagnoses and assessment of the relationship between SII and established severity scores, including APACHE II and Glasgow Coma Scale (GCS). The findings may support the use of SII as a rapid, inexpensive prognostic marker in critically ill patients.

Study Overview

• Status: Completed
• Conditions: Sepsis; Critical Illness
• Intervention / Treatment: Other: Systemic Immune-Inflammation Index (SII)

Detailed Description

Systemic inflammation is a fundamental component of critical illness and has a strong association with disease severity and mortality in intensive care units. The Systemic Immune-Inflammation Index (SII), calculated from neutrophil, lymphocyte, and platelet counts, has emerged as a quantitative marker of systemic immune-inflammatory status. While SII has been studied in various clinical settings, its prognostic value in reanimation ICU patients remains insufficiently defined.

This study is designed as a single-center, retrospective, non-interventional cohort study conducted in the Reanimation Intensive Care Unit of Atatürk University Research Hospital. Adult patients (≥18 years) admitted to the ICU for infectious or non-infectious critical illnesses will be evaluated through retrospective review of hospital electronic medical records (ENLİL Hospital Information Management System).

Patients will be included if admission laboratory data, including complete blood count and biochemical parameters, are available. Exclusion criteria include pregnancy, hematologic malignancy, active chemotherapy, chronic immunosuppression, pulse steroid therapy, known severe thrombocytopenia (<50×10⁹/L), massive bleeding or massive transfusion within the first 24 hours, and incomplete clinical or laboratory data.

The primary outcome of the study is the association between admission SII levels and ICU mortality. Secondary outcomes include comparison of mortality rates between infectious and non-infectious admission diagnoses, evaluation of correlations between SII and APACHE II and GCS scores, and assessment of whether elevated SII is an independent risk factor for ICU mortality.

Sample size calculation was performed using G*Power software based on a reference population study, assuming a mean SII value of 515±170 in the control group. To detect a 40-unit difference in SII between infectious and non-infectious groups with 80% power and a 95% confidence level, a minimum of 285 patients per group (total ≥570 patients) is required.

Statistical analysis will be conducted using appropriate correlation tests (Pearson or Spearman) based on data distribution. As a retrospective, non-interventional study, no additional procedures will be performed, and patient confidentiality will be strictly maintained. The study involves no external funding and no declared conflicts of interest.

• Study Type: Observational
• Enrollment (Actual): 570

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Erzurum, Turkey (Türkiye), 25100
    • Atatürk University Faculty of Medicine Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Adult patients aged 18 years or older admitted to the reanimation intensive care unit for infectious or non-infectious critical illness, with available admission laboratory data

Description

Inclusion Criteria:

• Age 18 years or older
• Admission to the reanimation intensive care unit
• Availability of admission complete blood count and biochemical laboratory data
• Admission due to infectious or non-infectious critical illness

Exclusion Criteria:

• Pregnancy
• Hematologic malignancy
• Active chemotherapy
• Chronic immunosuppression
• Pulse steroid therapy
• Known thrombocytopenia (platelet count <50×10^9/L)
• Massive bleeding or massive transfusion within the first 24 hours of ICU admission
• Incomplete clinical or laboratory data

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
High Systemic Immune-Inflammation Index (High SII); Critically ill patients admitted to the intensive care unit with a systemic immune-inflammation index (SII) above the predefined cutoff value calculated at ICU admission. SII is calculated as platelet count × neutrophil count / lymphocyte count. Outcomes including ICU mortality are evaluated observationally without any intervention.	Other: Systemic Immune-Inflammation Index (SII); Systemic immune-inflammation index (SII) calculated at intensive care unit admission using routine complete blood count parameters. SII is calculated as platelet count multiplied by neutrophil count divided by lymphocyte count. Patients are classified into high and low SII groups based on a predefined cutoff value. No therapeutic intervention is administered as part of the study.
Low Systemic Immune-Inflammation Index (Low SII); Critically ill patients admitted to the intensive care unit with a systemic immune-inflammation index (SII) at or below the predefined cutoff value calculated at ICU admission. SII is calculated as platelet count × neutrophil count / lymphocyte count. Outcomes including ICU mortality are evaluated observationally without any intervention.	Other: Systemic Immune-Inflammation Index (SII); Systemic immune-inflammation index (SII) calculated at intensive care unit admission using routine complete blood count parameters. SII is calculated as platelet count multiplied by neutrophil count divided by lymphocyte count. Patients are classified into high and low SII groups based on a predefined cutoff value. No therapeutic intervention is administered as part of the study.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
ICU Mortality Rate	All-cause mortality during ICU stay, compared between patients with high vs. low SII values	Duration of ICU stay (up to 90 days)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Systemic Immune-Inflammation Index (SII)	SII calculated as neutrophil count × platelet count / lymphocyte count from admission peripheral blood sample	At ICU admission (Day 0)
APACHE II Score	Correlation between admission SII level and APACHE II score	First 24 hours of ICU admission
Glasgow Coma Scale (GCS) Score	Correlation between admission SII level and GCS score	At ICU admission (Day 0)

Collaborators and Investigators

• Sponsor: Ataturk University
• Investigators: Principal Investigator: nazim doğan, MD, Ataturk University Faculty of Medicine, Department of Anesthesiology and Reanimation

Study record dates

Study Major Dates

• Study Start (Actual): December 1, 2025
• Primary Completion (Actual): March 18, 2026
• Study Completion (Actual): March 18, 2026

Study Registration Dates

• First Submitted: February 19, 2026
• First Submitted That Met QC Criteria: March 21, 2026
• First Posted (Actual): March 25, 2026

Study Record Updates

• Last Update Posted (Actual): March 25, 2026
• Last Update Submitted That Met QC Criteria: March 21, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: intensive care unit; mortality; systemic immune-inflammation index
• Additional Relevant MeSH Terms: Pathologic Processes; Disease Attributes; Infections; Systemic Inflammatory Response Syndrome; Inflammation; Pathological Conditions, Signs and Symptoms; Critical Illness; Sepsis
• Other Study ID Numbers: B.30.2.ATA.0.01.00/804

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No