This retrospective observational study evaluates the prognostic value of the C-reactive protein-albumin-lymphocyte (CALLY) index in adult patients with sepsis admitted to the intensive care unit (ICU). The CALLY index reflects inflammatory, nutritional, and immunologic status and may serve as a predictor of clinical outcomes.

CALLY Index values will be obtained on Day 0, Day 3, and Day 5 of ICU admission using routinely collected laboratory data. The primary objective is to determine the association between CALLY Index values and 30-day all-cause mortality. Secondary objectives include assessing the relationship between temporal CALLY changes and the development of acute kidney injury (AKI) within the first 7 days of ICU admission, as well as correlations between the Day-0 CALLY Index and established severity scores such as SOFA and APACHE II.

As this retrospective study uses existing electronic medical records, no additional procedures or interventions will be performed, and no added risk to patients is involved.

Sepsis is a life-threatening condition characterized by a dysregulated host response to infection and is frequently associated with multiorgan dysfunction and high mortality. Early identification of patients at increased risk of poor outcomes remains a major challenge in critical care. The C-reactive protein-albumin-lymphocyte (CALLY) Index is a composite biomarker that reflects inflammatory, nutritional, and immune status. Although recent studies have explored the prognostic value of CALLY in critically ill populations, the significance of serial measurements and temporal changes in patients with sepsis has not been fully established.

This retrospective observational study will include adult patients diagnosed with sepsis according to Sepsis-3 criteria who were admitted to the intensive care unit (ICU) between January 2023 and December 2024. The CALLY Index will be calculated using the following formula:

Albumin (g/L) × lymphocyte count (10⁹/L) × 100 ÷ CRP (mg/L).

CALLY values will be obtained at predefined time points: Day 0 (within 2 hours of ICU admission), Day 3, and Day 5, extracted from the hospital's electronic medical record system.

The primary aim of the study is to evaluate the association between CALLY Index values and 30-day all-cause mortality. Secondary aims include assessing the relationship between temporal changes in CALLY (ΔCALLY₃-₀, ΔCALLY₅-₀, and linear trend slope) and the development of acute kidney injury (AKI) within the first 7 days of ICU admission, as well as examining correlations between the Day-0 CALLY Index and commonly used clinical severity scores, including SOFA and APACHE II.

All study data will be obtained retrospectively from the hospital's electronic records. No additional tests, procedures, or interventions will be performed. As the study utilizes existing clinical data without influencing patient management, it poses no additional risks to participants. The findings may support improved early risk stratification, monitoring of disease progression, and refinement of prognostic assessment in patients with sepsis.

Inclusion Criteria:

• Age ≥ 18 years

  • Sepsis diagnosis meeting Sepsis-3 criteria
  • ICU stay ≥ 5 days
  • Complete CRP, albumin, and lymphocyte laboratory results available for days 0, 3, and 5

Exclusion Criteria:

• • Chronic Kidney Disease stage ≥3

  • Liver diseases including cirrhosis, chronic hepatitis, or hepatic failure
  • Hematologic diseases such as leukemia, lymphoma, MDS, or multiple myeloma
  • Rheumatologic diseases including SLE, rheumatoid arthritis, or systemic sclerosis
  • Use of immunosuppressive therapy
  • ICU stay shorter than 5 days
  • COVID-19 positive status
  • Missing laboratory data preventing calculation of CALLY index

Adult ICU patients diagnosed with sepsis and treated at Ankara University Medical Faculty Hospital.