Abstract
This study aims to investigate the potential of the red cell distribution width to total calcium ratio (RCR) as a biomarker for in-hospital mortality in patients with non-idiopathic pulmonary fibrosis (IPF) interstitial lung diseases. A retrospective cohort analysis was carried out utilizing the Medical Information Mart for Intensive Care database, including 1138 patients with non-idiopathic pulmonary fibrosis interstitial lung diseases. Patients were divided into a survivor group (n = 1023) and a non-survivor group (n = 115) based on in-hospital mortality. The Boruta algorithm combined with a machine learning-based random forest algorithm was employed to calculate Shapley Additive Explanations (SHAP) values to identify clinical indicators significantly contributing to in-hospital mortality. A nomogram model based on logistic regression was constructed to assess the relationship between RCR and in-hospital mortality. Compared to the survivor group, the non-survivor group's average age was significantly older (73.00 ± 10.67 years vs 69.83 ± 13.24 years, P = .013), and RCR was significantly elevated in the non-survivor group (1.83 ± 0.30 vs 1.73 ± 0.27, P <.001). After adjusting for white blood cell count, blood urea nitrogen (BUN), sodium levels, and pneumonia in the model, the odds ratio for RCR was 2.283 (95% CI: 1.108-4.649, P = .024). BUN was identified as a mediator, accounting for approximately 14.6% of the indirect effect. Subgroup analyses revealed a stronger association of RCR with in-hospital mortality in female patients, those aged ≤65 years, and patients with hypertension. The nomogram model's C-index was 0.771 for the training set and 0.764 for the validation set. The training set's area under the curve was 0.771 (95% CI: 0.712-0.829), while the validation set's was 0.764 (95% CI: 0.706-0.821). RCR serves as a simple and effective biomarker for predicting in-hospital mortality risk in patients with non-idiopathic pulmonary fibrosis, with BUN playing a mediating role in this association.