Pilot study of diagnostic performance of serum creatinine/cystatin C ratio for pseudo-acute kidney injury

Introduction:We conducted a proof-of-concept study to evaluate the diagnostic performance of the serum creatinine/cystatin C ratio (CrCyR) in distinguishing pseudo-acute kidney injury (AKI) from true AKI. Methods:This study included patients with confirmed AKI (excluding rhabdomyolysis) at the First Affiliated Hospital of Nanjing Medical University (May 2023-August 2024) and pseudo-AKI cases identified through a literature review (1994-2025).CrCyR values (unit: L/dL) measured before (CrCyR pre ) and during AKI onset (CrCyR post ) were collected.Diagnostic performance of CrCyR post was assessed using the area under the receiver-operating-characteristic curve (AUC). Results: Of 239 patients, 197 had true AKI and 42 had pseudo-AKI (mechanisms: reduced creatinine excretion [n=18], assay interference [n=14], urine leakage [n=7], and increased creatinine production [n=3]).Median CrCyR post was significantly higher in the pseudo-AKI group than in the true AKI group (1.89 [IQR, 1.32-3.28]vs. 0.78 [0.64-0.94]L/dL; P<0.001).CrCyR post showed a preliminary AUC of 0.97 (95% CI, 0.95-1.00);an exploratory threshold of >1.11 L/dL yielded 95% sensitivity and 91% specificity for diagnosing pseudo-AKI.After adjustment for age and sex, the covariate-adjusted AUC remained high at 0.98 (0.96-1.00).Diagnostic utility was consistently high across pseudo-AKI subtypes (AUCs: 1.00 for assay interference, urine leakage, and increased creatinine production; 0.94 for reduced creatinine excretion).A cross-center robustness assessment using true AKI patients from the Salzburg Intensive Care database suggested consistent diagnostic utility (AUC 0.94 [0.90-0.98]) in Europeans. Conclusion:CrCyR post preliminarily demonstrates promising diagnostic accuracy for distinguishing pseudo-AKI from true AKI.Further validation in prospective studies is warranted.