Exploratory Evaluation of Potential CRP and Ferritin Thresholds and Survival in Critically Ill Patients: A Pilot Prospective ICU Study

Background/Objectives: Iron deficiency is a common condition in the general population, with a higher incidence in critically ill patients. Anemia associated with these alterations is linked to increased morbidity and mortality in ICU patients. This pilot study explores whether provisional CRP and ferritin thresholds might relate to survival, and examines the preliminary associations with analytical and clinical variables in critically ill patients. Methods: A prospective, observational pilot study was conducted on 75 ICU patients over three months. Hematological and biochemical parameters (CRP, ferritin, iron, transferrin, hemoglobin) were analyzed at admission, 48 h, and on days 4 and 7. Clinical data included age, sex, ICU stay, survival, SOFA and APACHE II scores, complications (AKI, acute lung injury), and interventions (mechanical ventilation, infections). Data were analyzed using mixed regression models and Wilcoxon tests. Results: In this pilot cohort (mean age 53.65 years; 61.33% male), survival was 82.67%. Higher CRP and ferritin levels were observed among non-survivors and those with AKI p < 0.05. A CRP level ≥145 mg/L was associated with a constellation of more unfavorable clinical indicators (older age, longer ICU stay, higher APACHE II and SOFA scores, more mechanical ventilation, higher AKI and infection rates, and reduced survival) p < 0.05. Ferritin levels were higher in males and non-survivors and showed positive correlations with SOFA score and ICU length of stay. The exploratory prognostic performance of the CRP threshold was AUC = 0.8103. Conclusions: Elevated CRP and ferritin concentrations were associated with reduced survival probability and indicators of greater clinical severity in critically ill patients. The provisional thresholds identified in this pilot study (CRP ≥ 145 mg/L, ferritin ≥ 300 ng/mL) may facilitate early risk stratification; however, these findings remain exploratory and require validation in larger, multicenter cohorts before clinical translation.