ORIGINAL ARTICLE Acute kidney injury in premature newborns—definition, etiology, and outcome Vesna Stojanović 1 & Nenad Barišić 1 & Tanja Radovanović 2 & Milena Bjelica 2 & Borko Milanović 1 & Aleksandra Doronjski 1 Received: 30 October 2016 /Revised: 19 April 2017 /Accepted: 24 April 2017 # IPNA 2017 Abstract Background Neonatal acute kidney injury (AKI) is common and is associated with poor outcomes. New criteria for the diagnosis of AKI were introduced based on the increase in serum creatinine (SCr) levels and/or reduction of urine output (UOP). Yet, there is no generally accepted opinion so far, which criteria (whether SCr, UOP, or their combination) are the most appropriate to diagnose neonatal AKI. Methods The retrospective study included 195 prematurely born neonates who fulfilled all inclusion criteria (with at least two SCr measurements). In all the neonates included in the study, AKI was diagnosed using three different definitions: (1) SCr criteria (an increase in SCr values of ≥0.3 mg/dl), (2) UOP criteria (UOP < 1.5 ml/kg/h), and (3) SCr + UOP criteria. Results Out of all of the patients the study included, 85 (44%) were diagnosed with AKI. The neonates who had AKI had a significantly lower gestational age, birth weight, and Apgar score, longer duration of mechanical ventilation, and a higher mortality rate. SCr + UOP criteria showed higher sensitivity for prediction of death compared to SCr or UOP alone (p = 0.0008, 95% CI 0.040–0.154, and p = 0.0038, 95% CI 0.024–0.125, respectively). If only SCr or only UOP criterion are used, they fail to identify AKI in 61 and 67%, respectively. AKI was an independent risk factor for death (OR 7.4875; CI 3.1887–17.5816). Conclusions Similar to other studies, our data showed that neonates with AKI have worse outcome. Neonatal AKI de- fined based on SCr + UOP criteria is a better predictor of death than neonatal AKI defined based only on the SCr or UOP criteria. Also, by using SCr + UOP criteria for diagnosing neonatal AKI, more patients with AKI are recruited than when only one of those criteria is used. Keywords Acute kidney injury . Risk factors . Definition . Preterm infants Introduction Acute kidney injury (AKI) is characterized by the reduction in kidney function resulting in the accumulation of nitrogenous waste products, derangements in the fluid balance, and the loss of electrolyte and acid–base homeostasis. Among the neonates hospitalized in Neonatal Intensive Care Units (NICUs), the incidence of AKI ranges from 2.4– 54% [1–6]. It is well known that the children who survive an episode of AKI have increased risk from chronic kidney dis- ease (CKD) later in life [7–14]. So, it is obvious that neonatal AKI is common and is associated with poor outcomes. Preterm neonates have impaired glomerulogenesis, and this impairment is more pronounced in those neonates who had AKI. Glomerular injury during development causes a signifi- cant reduction in total number of nephrons. A compensatory hypertrophy of the glomeruli consequently causes distinct im- pairment of glomerular function characterized by increased intracapillary hydraulic pressures, which on the other hand, injures capillary walls. Over time, this series of events leads to progressive glomerulosclerosis, proteinuria, hypertension, and chronic kidney disease. However, valid conclusions re- garding short- and long-term outcomes are vague because * Vesna Stojanović vesna.stojanovic@mf.uns.ac.rs 1 School of Medicine, Institute for Child and Youth Health Care of Vojvodina, University of Novi Sad, Hajduk Veljkova 10, Novi Sad 21000, Serbia 2 Institute for Child and Youth Health Care of Vojvodina, Hajduk Veljkova 10, Novi Sad 21000, Serbia Pediatr Nephrol DOI 10.1007/s00467-017-3690-8