Abstract: Objective To investigate whether subclinical acute kidney injury (AKI) based on urinary cystatin C (uCys C) is associated with adverse outcomes in critically ill neonates. Methods Critically ill neonates admitted to the neonatal intensive care unit (NICU) from July to October 2016 were selected as the study subjects. The levels of uCys C were detected within 1 week after NICU admission. The optimal peak uCys C cutoff value of the ROC curve for predicting mortality was used to determine the presence of tubular injury. The presence of renal tubule injury without AKI （uCys C(+)/AKI(?)） was defined as subclinical AKI. Neonates were divided into death group and survival group according to whether they died during hospitalization. According to the presence or absence of tubular damage and/or AKI, neonates were divided into four groups. The clinical characteristics of neonates in different groups were compared. Results A total of 246 critically ill neonates (136 boys and 110 girls) were included, with a median age of 1.0 (1.0-2.0) d. Among them, 30 neonates developed AKI within one week of admission to the NICU and 24 neonates died during their stay in the NICU. Binary logistic regression analysis showed that the levels of first and maximum uCys C were independent risk factors for neonatal death after adjusting for confounding factors (P<0.05). According to ROC curve results, 82 neonates (33.3%) developed subclinical AKI, with the maximum uCys C level >1558 ng/mg as the presence of renal tubular injury. The score for neonatal acute physiology (SNAP) of neonates in the subclinical AKI group was higher than that in the uCys C(?)/AKI(?) group, but lower than that in the uCys C(+)/AKI(+) group. The length of NICU stay in the subclinical AKI group was longer than that in the uCys C(?)/AKI(?) and uCys C(?)/AKI(+) groups, and the differences were statistically significant. Conclusions Subclinical AKI is associated with adverse outcomes of critically ill neonates.

Key words: critically ill neonates; urinary cystatin C; acute kidney injury; mortality