Plasma cystatin C versus renal resistive index as early predictors of acute kidney injury in critically ill neonates.

INTRODUCTION: Acute kidney injury (AKI) independently predicts morbidity and mortality of critically ill neonates. Serum cystatin C is a promising early biomarker for AKI. Evaluating the renal resistive index (RRI) by Doppler ultrasound demonstrates abnormal intrarenal vascular impendence.

OBJECTIVE: The objective of this study was to compare the ability of plasma cystatin C and the RRI to predict AKI early in critically ill neonates.

STUDY DESIGN: Sixty critically ill neonates in neonatal intensive care units were assigned to three groups: group 1 (cases) of thirty participants fulfilling the AKI diagnostic criteria of neonatal Kidney Disease Improving Global Outcome, group 2 of thirty participants not fulfilling the criteria, as well as the 3rd group of thirty age- and sex-matching healthy participants.

RESULTS: Group 1 demonstrated a significantly high mean cystatin C level during the 1st day of incubation compared with the other two groups [group 1 (3.18 ± 1.25), group 2 (1.68 ± 0.66), and group 3 (0.80 ± 0.26)]. Serum creatinine and RRI were insignificantly different among all groups. At a cutoff value of 2.68 (mg/l), cystatin C level had significantly higher area under the curve (AUC) (0.804) than both serum creatinine (0.453) and RRI (0.551) and had 53.3% sensitivity and 100% specificity in the early prediction of neonates with AKI. The RRI had a lower non-significant AUC (0.551) at a cutoff value of 0.53 and had 100% sensitivity and 40% specificity, while serum creatinine had a low non-significant AUC (0.453) at a cutoff value of 0.49 (mg/dl) and had 33.3% sensitivity and 86.7% specificity. Applying regression analysis to predict AKI in critically ill neonates as early as possible, higher plasma cystatin C and lower estimated glomerular filtration rate cystatin were the only independent risk factors within critically ill neonates.

CONCLUSIONS: The level of plasma cystatin C increased 48 h before both RRI and serum creatinine did in critically ill neonates who developed AKI, so it is more reliable in predicting AKI in critically ill neonates than serum creatinine and RRI.