Diabetic nephropathy, a severe complication of diabetes, significantly increases the risk of mortality, particularly among patients in intensive care units where metabolic disturbances are pronounced. Globally, the prevalence of DN is rising, imposing a growing economic and public health burden. While alterations in red blood cell distribution width (RDW) and serum calcium levels are common in critically ill patients and have been linked to DN progression, the predictive value of the RCR ratio for mortality remained largely unexplored until now.
Researchers, led by Dr. Jianlu Bi from the Endocrinology Department at Guangdong Second Hospital of Traditional Chinese Medicine, Guangzhou, China, analyzed data from the MIMIC-IV database to investigate this relationship. The study included 1,265 critically ill DN patients, with a median age of 73 years and 64.27% being male. Patients were categorized into four groups according to their RCR index, and mortality outcomes were assessed at 30, 90, 180, and 365 days. Kaplan-Meier curves, Cox proportional hazards regression, and restricted cubic spline (RCS) analyses were applied to examine the association between RCR values and all-cause mortality.
The analysis revealed the following findings:
- Higher RCR values were associated with increased mortality risk at all assessed time points.
- Patients in the highest RCR quartile faced significantly elevated mortality risks according to Cox regression analysis.
- Restricted cubic spline (RCS) analysis showed a linear relationship between RCR and all-cause mortality.
- Inflection points were identified at 2.361 for 30-day mortality and 2.098 for 365-day mortality.
- Each unit increase in RCR below 2.361 was linked to a 414% increase in 30-day mortality.
- Each unit increase in RCR below 2.098 was linked to a 494% increase in 365-day mortality.
- The findings highlight the prognostic significance of the RCR index in critically ill diabetic nephropathy patients.
Despite the robust findings, the study acknowledged several limitations. Being a retrospective single-center ICU analysis, its generalizability to non-ICU populations remains uncertain. The database did not provide DN-specific mortality causes, dialysis status, or detailed renal function parameters, which may influence outcomes. Approximately 20% of variables with missing data were excluded, though interpolation methods were applied to mitigate this limitation. The authors emphasized that causal relationships could not be definitively established due to the study design.
The study highlights the clinical value of RCR as a readily available biomarker derived from routine laboratory tests. Elevated RCR levels may assist clinicians in identifying high-risk DN patients and tailoring ICU treatment strategies accordingly. The researchers advocate for larger, multicenter prospective studies to validate RCR’s utility and explore its integration into routine risk assessment for patients with diabetic nephropathy.
"The findings suggest that the RCR index could serve as an important tool in predicting mortality risk among critically ill DN patients, potentially supporting better-informed clinical decisions and improving patient outcomes in intensive care settings," the authors concluded.
Reference:
Huang, Y., Jiang, K., Liu, Y. et al. 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. BMC Nephrol 26, 475 (2025). https://doi.org/10.1186/s12882-025-04402-x
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