Red blood cell distribution width to albumin ratio predicts mortality in heart failure patients with pneumonia

Background Heart failure (HF) patients with pneumonia admitted to the intensive care unit (ICU) face high mortality risks, yet current risk stratification tools lack precision. This study aims to evaluate the prognostic value of the red blood cell distribution width to albumin ratio (RAR) and develop a machine learning model for predicting 31-day in-hospital mortality in HF patients with pneumonia in ICU. Methods We included the MIMIC-IV cohort and an external validation cohort from the First Affiliated Hospital of Zhengzhou University. The restricted cubic spline (RCS), Kaplan–Meier, and multivariable Cox regression analyses were used to estimate the RAR's prognostic value for 31-day in-hospital mortality. Boruta-selected features were used to build eight machine learning models. Results In the Medical Information Mart for Intensive Care -IV (MIMIC-IV) cohort (n = 3, 158), RCS revealed a linear relationship between RAR and all-cause mortality. Patients were subsequently stratified into high- and low-risk groups based on the median RAR value. Kaplan–Meier analysis showed higher mortality in patients with above-median RAR (P 0. 05), and each unit increase in RAR independently predicted a 13% higher mortality risk (HR 1. 13, 95% CI 1. 06–1. 21; P 0. 001). Subgroup and sensitivity analyses confirmed RAR's prognostic consistency across demographic strata, comorbidities, and medication regimens. The LightGBM model, trained on Boruta-selected 13 optimal features, was identified as the best prediction model and demonstrated strong generalizability in internal (AUC = 0. 735) and external validation cohort (n = 1, 110 patients) (AUC = 0. 733). SHapley Additive exPlanations analysis ranked RAR as the second most critical predictor in the model. A web-based tool (https: //mengzhaoyang. shinyapps. io/PneumoHF-RARPredictor/) was developed for real-time risk assessment. Conclusions This study identifies RAR as an effective prediction biomarker for HF patients with pneumonia and provides a clinical tool for precise risk profiling.