Prognostic Implications of a Cumulative Renal Score Based on Both Serum Creatinine and Urine Output Criteria for Staging of Acute Kidney Injury: A Cohort Study

Purpose: Traditionally, the Kidney Disease: Improving Global Outcomes (KDIGO) stages acute kidney injury (AKI) into three stages based on the highest severity of increase in serum creatinine (SC) or urine output (UO) criteria. Clinically, however, the two criteria do not provide equivalent information. Thus, we aimed to develop a cumulative renal score (the sum of the highest KDIGO SC and UO severity stages) for staging of AKI, expanding the original three KDIGO stages to six stages. We hypothesized that the cumulative renal score would more accurately describe AKI severity and outcomes. Patients and Methods: Critically ill adult patients were identified from the Multi-parameter Intelligent Monitoring in Intensive Care III Database. The primary outcome was hospital mortality. Logistic regression was used to explore the association between cumulative renal score and hospital mortality. Results: A total of 17,404 critically ill adult patients were enrolled. Patients with higher cumulative renal scores had greater hospital mortality than patients with lower cumulative renal scores (score 0, 7.6%; score 1, 9.3%; score 2, 12.5%; score 3, 18.9%; score 4, 27.1%; score 5, 34.7%; score 6, 46.8%, p < 0.001). After adjustment for significant covariates, relative to cumulative renal score 0, cumulative renal scores 2-6 were associated with increased hospital mortality. Within the traditional KDIGO stage 2 AKI, when compared with cumulative renal score 2, cumulative renal score 4 had increased hospital mortality. Within the traditional KDIGO stage 3 AKI, when compared with cumulative renal score 3, cumulative renal score 6 had increased hospital mortality. Conclusion: Our study demonstrates that the KDIGO SC and UO criteria have a cumulative effect on AKI severity staging. The cumulative renal score improves the traditional KDIGO AKI staging by applying the two sets of criteria sequentially and provides more insight into the relationship between AKI and outcomes.