Association between red blood cell distribution width-to-albumin ratio and ICU/hospital mortality in patients receiving mechanical ventilation within 24 hours of ICU admission: A multicenter retrospective study

Objective To assess the association of early red blood cell distribution width-to-albumin ratio (RAR) with mortality in mechanically ventilated ICU patients and its value alongside routine clinical assessment. Methods This retrospective cohort study used MIMIC-IV and eICU-CRD data. Adults receiving invasive mechanical ventilation within 24 hours of ICU admission who remained in the ICU at 24 hours were included. RAR was calculated from first-day laboratory measurements. Multivariable Cox regression assessed its association with subsequent in-hospital and ICU mortality. Additional analyses examined whether RAR improved prediction beyond its components and established severity scores. Results The study included 3,534 MIMIC-IV patients and 1,929 eICU-CRD patients. Compared with the lowest RAR quartile, the highest quartile was associated with greater in-hospital mortality in both databases (adjusted HR 1.855, 95% CI 1.474–2.335, and HR 1.698, 95% CI 1.231–2.341, respectively). The corresponding ICU mortality association was significant in MIMIC-IV but not in eICU-CRD. Adding RAR to clinical models improved discrimination and reclassification for in-hospital mortality, with performance similar to including RDW and albumin separately. Improvements beyond severity scores varied by outcome and measure. Conclusions Higher first-day RAR was associated with subsequent in-hospital mortality among mechanically ventilated adults in two ICU databases. RAR may provide supplementary prognostic information, although its role in clinical decisions requires prospective evaluation.