Association between red blood cell distribution width to serum calcium ratio and all-cause mortality in critically ill patients with diabetic nephropathy: a retrospective analysis of the MIMIC-IV database.

Abstract

Background: Diabetic nephropathy (DN) is a critical diabetes complication that raises mortality risk, particularly in intensive care unit (ICU) settings where metabolic disturbances are more pronounced. The prevalence and economic burden of DN are growing globally, posing a major public health challenge. Red blood cell distribution width (RDW) and serum calcium (SC) levels, which frequently exhibit significant alterations in critically ill patients, are linked to DN progression. However, the role of the RDW to SC (RCR) ratio in predicting mortality among critically ill DN patients remains understudied. This study aims to explore the RCR index's relationship with mortality in ICU patients with DN, aiding high-risk patient identification and prognostic strategy formulation in critical care settings.

Methods: Data was sourced from the Medical Information Mart for Intensive Care (MIMIC-IV) database. Patients were categorized into four groups based on their RCR index. Primary endpoints were 30-day and 365-day all-cause mortality; secondary endpoints were 90-day and 180-day mortality. Kaplan-Meier curves were used to visualize outcomes by quartiles. Cox proportional hazards regression and restricted cubic spline (RCS) methods assessed the RCR index's impact on prognosis. Subgroup analyses were also conducted.

Results: Among 1,265 participants (median age: 73.00 years; 64.27% male), higher RCR index values were associated with increased all-cause mortality risks at 30, 90, 180, and 365 days (Kaplan-Meier curves, log-rank P < 0.01). Cox regression revealed higher mortality risks for patients in the highest quartile. RCS analysis showed a linear relationship between the RCR index and all-cause mortality, with inflection points at 2.361 (30-day mortality) and 2.098 (365-day mortality). Specifically, each unit increase below 2.361 in the RCR index was associated with a 414.0% increased 30-day mortality risk (P < 0.001; 95% CI: 3.041-8.688). For 365-day mortality, each additional unit below 2.098 increased risk by 494.2% (P < 0.001; 95% CI: 3.733-9.458).

Conclusion: The RCR index exhibits a linear relationship with all-cause mortality in DN patients. It may serve as a useful indicator for assessing disease severity and guiding ICU treatment decisions, enhancing clinician decision-making and patient outcomes.