EXPRESS: The CRP/Albumin Ratio (CAR) may be more strongly linked to delirium than other indices derived from laboratory parameters in older patients in an intensive care unit

The aim of this study is to investigate the association of delirium with laboratory-derived indices and ratios in patients staying in an intensive care unit (ICU). Delirium was diagnosed according to DSM-5 criteria, and laboratory data obtained at the time of diagnosis were retrospectively analyzed. The following indices were calculated: C-reactive protein(CRP)/albumin ratio(CAR), CRP-albumin-lymphocyte(CALLY), B12-CRP(BCI), Systemic Immune-Inflammation(SII), Prognostic Nutritional Index(PNI), Advanced Lung Cancer Inflammation (ALI), Systemic Inflammation Response indices (SIRI) and Glasgow Prognostic Score (GPS). In addition, inflammation markers derived from the complete blood count were also analyzed. They were compared between patients with and without delirium. The study included 215 patients, of whom 104 had delirium (median age 76 years, 51.6% female). Patients with delirium were older than those without delirium(p=0.008). The median CAR index was higher in patients with delirium (3.4 mg/g, 0.02–28.23) compared to those without delirium (2.19 mg/g,0.02–16.74), with borderline statistical significance(p=0.071). No statistically significant differences were found in other indices and laboratory parameters between patients with delirium and those without it (p>0.05 for all). When patients were stratified into tertiles based on CAR levels, the occurrence of delirium was significantly higher in the third tertile than in the other two tertiles (p=0.020). Even after adjusting for all significant confounding factors, CAR remained independently associated with delirium [Odds ratio(OR):1.099, 95% confidence interval(CI):1.002–1.205, p=0.046]. The findings of this study suggest that the CAR index may serve as an independent associated factor for delirium compared to other laboratory-derived markers in critically ill patients.