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 was aimed to evaluate the diagnostic ability of serum Cystatin-C and Renal Resistive Index in prediction of AKI among critically ill patients.

Methodology: This prospective observational study was carried out in the department of Medicine, over a period of one year. After informed consent and ethical clearance total 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 Intensive care unit (ICU). Serum cystatin C was measured on day 1 by particle-enhanced immune nephelometric assay, Renal resistive index (RRI) calculated by ratio of the velocities of arterial perfusion throughout the cardiac phase and glomerular filtration rate was measured on days 1, 3, and 7 respectively.

Results: S. cystatin C value was significantly higher(>3times) 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 day1, S. cystatin C, at cut off value of ≥9.29 mcg/ml had diagnostic accuracy 90% with sensitivity 91%, specificity89% and PPV 95.5%. While RRI value on day 7, at cut-off value of ≥0.72, had diagnostic accuracy 98%, sensitivity (98.6%) and specificity (96.7%) for AKI with 98.6% PPV, 96.7% NPV.

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