Age-Stratified Immune-Inflammatory Profiles and Prognostic Implications of Old Patients in the ICU: A Prospective Study

Hui Lian,1,* Guangjian Wang,1,* Qing Zhang,2 Hua Zhao,2 Xiaoting Wang2 1Department of Health Care, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing City, People’s Republic of China; 2Department of Critical Care Medicine, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing City, People’s Republic of China*These authors contributed equally to this workCorrespondence: Hua Zhao; Xiaoting Wang, Department of Critical Care Medicine, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, No. 1 Shuaifuyuan, Dongcheng District, Beijing City, 100730, People’s Republic of China, Email [email protected]; [email protected]: The aging population has advanced older patients (OPs) in intensive care units (ICUs). Critical illness and aging exacerbate immune-inflammatory dysregulation, impairing immune interactions and worsening prognosis. However, knowledge regarding immune-inflammatory profiles and prognostic implications for OPs, particularly in very old patients (VOPs), remains limited.Methods: This single-center prospective study included patients aged ≥ 65 with hemodynamically confirmed shock, signifying severe critical illness admitted between August 2023 and February 2025. Demographic, medication, and laboratory data were collected from electronic medical records. The primary endpoint was in-hospital mortality; secondary endpoints included ICU and hospital stay duration. Participants aged 65– 74 were young old patients (YOPs), and those aged ≥ 75 as VOPs. Statistical analysis included χ² for categorical variables, Kolmogorov–Smirnov for non-normal continuous data, Principal component analysis (PCA) for inflammatory states, while generalized additive mixed models for statistical interactions.Results: A total of 537 OPs were admitted, with no significant differences in inflammatory markers between YOPs and VOPs, except fibrinogen. Survivors had higher levels of hypersensitive C-reactive protein (hsCRP). Lymphocyte counts and subtypes were reduced in OPs. VOPs showed higher natural killer cells, CD8+CD38+, and CD8+DR+ counts versus YOPs. The median CD8+DR+ count was 82 in survivors versus 59 in non-survivors. Among VOPs, hsCRP, interleukin-8, and immunoglobulin G showed significant differences. B cell count was lower (median 104 vs 72), and CD8+ T cell activation declined in non-survivors. Mortality was higher in the low inflammatory state group. As B and T cell counts increased, mortality decreased in high inflammatory states. Higher CD8+DR+ counts reduced mortality.Conclusion: OPs, especially VOPs, with hemodynamically confirmed shock and critical illness exhibit distinct immune-inflammatory characteristics affecting prognosis. A weakened immune response in low inflammation links to poor outcomes. Enhancing B cell and CD8+DR+ T cell responses may improve prognosis through precise immune regulation in ICU settings.Keywords: old patient, critical illness, immune, inflammatory, interactions, lymphocyte subset, prognosis