Evaluation of ferritin and the ferritin index as prognostic biomarkers in septic shock

Background: Ferritin, an acute phase reactant, and the ferritin index (FI = observed ferritin level/upper limit of normal level for age and sex) may be prognostic biomarkers in septic shock and cardiac surgery patients. Objective: The purpose of this exploratory study is to assess the outcome associations of ferritin and FI levels in septic shock compared to post–cardiac surgery patients. Design: This was a prospective, double-centre, observational study. Setting: The study setting involved two adult intensive care units (ICUs) in Victoria, Australia. Participants: Sixty-one septic shock and 30 post–cardiac surgery patients participated in this study. Main outcome measures: We measured ferritin and FI on ICU admission (T1) and 24 h later (T2) to assess its correlation with mortality, illness severity, and hospital length of stay (LOS). Results: The baseline characteristics of patients in the septic shock group and cardiac surgery group were similar apart from illness severity scores (APACHE III and modified SOFA score). Septic shock patients had more physiological derangements as well as greater use and higher doses of norepinephrine at both T1 and T2. Septic shock patients had significantly higher median ferritin levels (372 μg/L versus 198 μg/L; p < 0.001 at T1, 457 μg/L versus 264 μg/L; p = 0.001 at T2) than post–cardiac surgery patients. Ferritin levels, however, did not have a linear correlation with illness severity or hospital mortality. Instead, there was an association between high ferritin levels at T2 and longer ICU (p = 0.017) and hospital LOS (p = 0.013). Females with septic shock had significantly higher FI (p < 0.001 at T1, p = 0.004 at T2) than males. Conclusion: In septic shock patients, ferritin levels and FI were twice the level compared to post-cardiac surgery patients. Both had no association with mortality, but levels above the median at 24 h were associated with longer ICU and hospital LOS.