A Universal Immune Index (II): A Composite Quantitative Assessment Method and Calculation Tool for Immune Function Based on Multidimensional Routine Laboratory Parameters

Background: Quantitative assessment of immune function is essential for clinical and health decisions in oncology, post-surgical management, and autoimmune diseases. Existing methods are either too simplistic (single indicators) or too complex and costly for routine use. A standardized, easy-to-operate tool based on routine laboratory parameters is needed for both clinical and health checkup settings. Methods: We propose the Immune Index (II), integrating 9 routine laboratory parameters across three dimensions: humoral immunity (IgG, complement C3, C4), cellular immunity (CD4+ T cells, CD8+ T cells, CD4+/CD8+ ratio), and inflammatory response (CRP, IL-6, systemic immune-inflammation index [SII]). Indicators were normalized using min-max normalization to a 0-100 scale and aggregated with fixed weights (humoral 30%, cellular 40%, inflammatory 30%). The II score ranges from 0 to 100, with a healthy reference range of 50-80. Results: A four-tier grading system was established: >=80 (immune overactivation), 50-80 (immune homeostasis), 35-50 (mild immune suppression), <35 (severe immune deficiency). Validation using 209 cases from published literature showed an AUC of 0.924 (95% CI: 0.87- 0.97) for distinguishing normal from abnormal immune status, with an optimal cutoff of 47.8 (sensitivity 84.8%, specificity 85.9%). II scores were 56.7+/-8.6 (healthy), 43.5+/-8.0 (immunodeficient), and 33.6+/-6.5 (autoimmune), with P<0.001 between all groups. The calculation requires only two steps and can be implemented in Excel or LIS. II can serve as an immune dimension supplement for personal health checkups. Conclusion: The Immune Index provides a simple, standardized, and low-cost tool for quantitative immune function assessment. The fixed-weight design ensures cross-institutional comparability, making it suitable for outpatient clinics, health checkup centers, and primary care settings. Keywords: Immune index; immune function; quantitative assessment; routine laboratory parameters; composite score; min-max normalization