The CALLY Index in Critical Illness: Risk Stratification and Its Potential Role in Clinical Monitoring

Background: Critically ill patients frequently exhibit concurrent inflammatory activation, nutritional depletion, and immune dysfunction. Although several laboratory-derived indices exist, there is a growing demand for simple, multi-dimensional prognostic markers in acute settings. The CALLY index integrates inflammatory burden, protein reserve, and immune competence. For intensive care practice, its greatest potential lies in rapid, cost-effective bedside risk stratification and dynamic monitoring. Methods: We conducted a systematic narrative review of studies published from January 2021 to February 2026 in PubMed, Web of Science, and Scopus. Eligible studies evaluated the CALLY index in adult populations and reported its association with at least 1 clinical outcome. A total of 56 studies met the inclusion criteria. Given substantial heterogeneity, a structured narrative review was performed rather than meta-analysis, with particular attention to sepsis and critically ill patients. Results: Across disease settings, lower CALLY values were generally associated with worse outcomes. The strongest evidence was observed in oncology and in sepsis/critical illness. Among ICU studies, lower CALLY values were associated with higher short-term mortality and greater disease severity. However, current evidence is limited by predominantly retrospective designs, variable cutoff values, and insufficient external validation of incremental value beyond established tools such as SOFA and APACHE II. Conclusions: CALLY is a simple, accessible composite biomarker for ICU risk assessment. While useful as an adjunct tool, prospective multicenter studies are required to define its optimal timing and incremental clinical utility in critical care.