Diagnostic Accuracy of Plasma Cystatin C and Renal Resistive Index for Acute Kidney Injury in Critically Ill Patients: A Prospective Observational Study

Background: Acute kidney injury (AKI) is a quite common problem in critically ill patients. Serum cystatin C has emerged as a marker of AKI. This study aimed to evaluate the diagnostic ability of serum Cystatin-C and Renal Resistive Index in predicting AKI among critically ill patients.

Methodology: This prospective observational study was carried out in the Department of Medicine, over one year. After informed consent and ethical clearance, a total of 120 critically ill patients suffering from sepsis were enrolled, out of which 70 patients developed AKI while 50 did not develop AKI during treatment in the Intensive care unit (ICU). Serum cystatin C was measured on day 1 by particle-enhanced immune nephelometric assay, Renal resistive index (RRI) was calculated by the ratio of the velocities of arterial perfusion throughout the cardiac phase, and glomerular filtration rate was measured on day 1, 3, and 7 respectively.

Results: S. cystatin C value was significantly higher(> 3 times) in AKI patients (14.07±4.8 mcg/ml) as compared to those who did not develop AKI (4.28±3.27 mcg/ml) (p 0.001). After ROC analysis it was found that day 1, S. cystatin C, at cut off value of ≥9.29 mcg/ml had diagnostic accuracy 90% with sensitivity 91%, specificity89%, and PPV of 95.5%. While RRI value on day 7, at a cut-off value of ≥0.72, had a diagnostic accuracy of 98%, sensitivity (98.6%), and specificity (96.7%) for AKI with 98.6% PPV, and 96.7% NPV.

Conclusion: Serum cystatin C appears to be a promising biomarker for early diagnosis of AKI in critically ill patients. Whereas RRI although non-invasive had good diagnostic accuracy it diagnosed AKI after a few days thus diagnosis of kidney injury was delayed.