Cystatin C as a Predictor of Severe Hospital-Acquired Pneumonia in Traumatic Brain Injury Patients: A Cohort Study

This study aimed to identify core differential proteins associated with severe hospital-acquired pneumonia (sHAP) complicating the hospitalization of traumatic brain injury (TBI) patients through proteomic analysis. It further explored their association with sHAP and evaluated their predictive value. This single-center cohort study collected general clinical characteristics and biological indicators from 153 TBI patients admitted to the neurosurgery department of Chongqing Emergency Medical Center between February 4, 2021, and May 10, 2024. We performed quantitative analysis of differential proteins associated with sHAP and identified Cystatin C (CysC) as a key differential protein. Logistic regression modeling assessed the correlation between serum CysC concentration at the 24-h cut-off point and the occurrence of sHAP. The predictive value of CysC for sHAP was evaluated using the Receiver Operating Characteristic (ROC) curve and the Kaplan-Meier method. The study included 153 TBI patients with a mean age of 48.7 ± 14.6 years, comprising 118 (77.1%) males and 35 (22.9%) females. Of these, 43 patients developed sHAP, with a mean CysC serum concentration of 120.8 ± 17.7 µg/L, while the 110 patients who did not develop sHAP had a mean CysC serum concentration of 92.7 ± 18.4 µg/L. After adjusting for multiple factors, each 1 µg/L increase in CysC levels was associated with a 9% increase in sHAP incidence (OR: 1.09, 95% CI: 1.06-1.13). In the ROC curve analysis, CysC demonstrated a sensitivity of 79.1% and specificity of 80.9% at a threshold of 111.75 µg/L, showing superior predictive efficacy compared with traditional inflammatory markers. Kaplan-Meier curves indicated a higher incidence of sHAP in TBI patients with CysC ≥111.75 µg/L. This study innovatively explored CysC at the proteomic level, identifying it as a key protein associated with sHAP in TBI patients. Our findings suggest that serum CysC levels may not only indicate renal function but also reflect systemic inflammation and other pathological states. Elevated CysC levels at 24 h post-admission were significantly linked to an increased risk of sHAP, with this association persisting after adjusting for relevant factors. Notably, CysC demonstrated superior accuracy in predicting sHAP compared with traditional inflammatory markers such as WBC and Neu#. Thus, CysC holds potential as a novel indicator for assessing sHAP risk in TBI patients post-admission. Further studies are needed to validate its clinical utility and broaden its application.