This study aims to evaluate the prognostic value of the C-reactive protein-albumin-lymphocyte (CALLY) index, Clinical Frailty Scale (CFS), and SOFA-2 score in predicting mortality among geriatric intensive care unit (ICU) patients.

The primary outcome is ICU mortality. Secondary outcomes include 28-day mortality, ICU length of stay, duration of mechanical ventilation, need for renal replacement therapy, and vasopressor requirement.

The study also investigates whether the combined use of these parameters improves predictive performance compared to conventional scoring systems such as APACHE II.

This is a single-center, prospective observational cohort study including patients aged ≥65 years admitted to the intensive care unit.

Demographic characteristics, comorbidities, frailty status (Clinical Frailty Scale), and severity scores (SOFA-2, APACHE II) will be recorded. Laboratory parameters including C-reactive protein, albumin, and lymphocyte count will be used to calculate the CALLY index within the first 24 hours of ICU admission.

Patients will be followed for ICU mortality and 28-day mortality. Additional outcomes include ICU and hospital length of stay, duration of mechanical ventilation, vasopressor requirement, and need for renal replacement therapy.

Statistical analyses will include logistic regression and receiver operating characteristic (ROC) curve analysis to evaluate the predictive performance of each parameter and their combined use.

Inclusion Criteria:

• Age ≥65 years
• Admission to the intensive care unit
• Availability of required clinical and laboratory data within the first 24 hours of ICU admission

Exclusion Criteria:

• Death within the first 24 hours after ICU admission
• Missing key clinical or laboratory data
• Terminal malignancy receiving palliative care

Geriatric patients (aged ≥65 years) admitted to the intensive care unit.

Individual participant data will not be publicly available due to institutional and ethical restrictions.