Acute kidney injury in very low birth weight infants: challenges, risk factors, and outcomes

Article information

Child Kidney Dis. 2025;29(1):1-3

Publication date (electronic) : 2025 February 28

doi : https://doi.org/10.3339/ckd.25.006

Jeong Yeon Kim¹

¹Department of Pediatrics, Chungnam National University Hospital, Daejeon, Republic of Korea

Correspondence to Jeong Yeon Kim Department of Pediatrics, Chungnam National University Hospital, 282 Munhwa-ro, Jung-gu, Daejeon 35015, Republic of Korea E-mail: kim.jy1117@gmail.com

Received 2025 January 20; Revised 2025 February 10; Accepted 2025 February 16.

Acute kidney injury (AKI) is a common and critical condition among neonates, especially in very low birth weight (VLBW) infants. It is characterized by an abrupt loss of kidney function, leading to a decline in glomerular filtration rate. Clinically, AKI is defined as an increase in serum creatinine level from baseline and/or a reduction in urine output. Various criteria, including Kidney Disease: Improving Global Outcomes (KDIGO), Pediatric Risk, Injury, Failure, Loss, End-Stage Renal Disease, and Acute Kidney Injury Network, are used to diagnose and define AKI [1]. In neonates, AKI is associated with prolonged hospital stays, increased morbidity, and higher mortality rates [2]. VLBW infants are particularly vulnerable to AKI due to their immature renal function and unique physiological characteristics. The diagnosis of AKI in this population is challenging. At birth, serum creatinine levels are influenced by placental equilibration and do not accurately reflect neonatal kidney function. Additionally, kidney maturation alters the function, complicating the assessment of renal health in the early postnatal period [3].

A recent systematic review and meta-analysis by Wu et al. [4] revealed an overall AKI incidence of 25% in premature neonates. However, the diagnosis of AKI in VLBW infants is complicated by difficulties in obtaining blood samples and the risk of anemia from repeated sampling [5]. In a previous issue of Childhood Kidney Diseases, Pasini et al. [6] investigated the incidence, risk factors, and mortality associated with AKI in VLBW infants. Newborns were monitored over the first 14 postnatal days using the modified neonatal KDIGO criteria, which incorporate both serum creatinine changes and urine output measurements. The incidence of AKI was reportedly 20%. In comparison, a systematic review and meta-analysis by Hirano Arruda Moraes et al. [7] reported variable AKI incidence ranging from 12% to 56%, influenced by differing diagnostic criteria. Notably, more than half of the studies in this review relied solely on serum creatinine levels without urine output monitoring, which likely contributed to the variability in the reported incidence rates. Pasini et al. [6] highlighted the limitations of relying exclusively on serum creatinine levels for AKI diagnosis. Among the VLBW infants diagnosed with AKI, 50% exhibited isolated abnormalities in serum creatinine levels, 30% had urine output abnormalities, and 20% showed both. These findings underscore the importance of monitoring both parameters, as up to 30% of AKI cases may be missed if urine output is not assessed. This comprehensive approach is particularly important for identifying cases of fluid overload associated with higher mortality rates and multi-organ dysfunction [8]. The relatively low AKI incidence in Pasini et al. [6] study compared to Hirano Arruda Moraes et al. [7] study might have been influenced by the limiting screening period of AKI incidence over first 14 postnatal days.

The risk factors of AKI in neonates remain multifaceted and complex. While previous studies, including those reviewed by Hirano Arruda Moraes et al. [7] identified factors such as patent ductus arteriosus, hemodynamic instability, sepsis, and invasive mechanical ventilation as significant contributors to AKI risk, Pasini et al. [6] found no statistically significant association between AKI and mechanical ventilation duration or early sepsis. Instead, the study identified a higher SNAPPE-II (Score for Neonatal Acute Physiology with Perinatal Extension-II) score, an indicator of illness severity within the first 12 hours of neonatal intensive care unit admission, as the primary risk factor for AKI. These differences highlight the variability in AKI risk factors across populations. Further research is required to clarify these relationships.

The effect of AKI on neonatal outcomes is profound. In the study by Pasini et al. [6], the overall mortality rate among VLBW infants was 11%; however, the mortality rate was significantly higher in the AKI group (35%) than in the non-AKI group (5%). AKI increases the risk of mortality approximately 10-fold. This finding is higher than the sevenfold increase reported by Hirano Arruda Moraes et al. [7], which may reflect the stricter diagnostic criteria used by Pasini et al. [6] The inclusion of urine output monitoring likely identified cases of fluid overload, a critical condition known to exacerbate mortality risk [8]. The long-term consequences of AKI in neonates can extend beyond the neonatal period. Pediatric patients with a history of AKI are at an increased risk of developing proteinuria, hypertension, chronic kidney disease, and other renal complications [9]. Despite these risks, data on the long-term outcomes of AKI in VLBW infants are limited. This knowledge gap underscores the need for longitudinal studies to better understand the renal and non-renal sequelae of AKI in this vulnerable population.

The study by Pasini et al. [6] identified two areas for improvement in future research. First, it focused exclusively on AKI events during the first two postnatal weeks, potentially underestimating the total risk when considering the entire neonatal intensive care unit stay. AKI episodes occurring later in the neonatal course may also have contributed to morbidity and mortality. Second, the study did not include renal ultrasound data, which could have provided insights into underlying renal abnormalities and their influence on the incidence and outcomes of AKI. A more comprehensive study on these areas will enhance future research, leading to a deeper understanding of AKI in neonates. In conclusion, AKI is a significant challenge in the care of neonates, particularly VLBW infants because of its high incidence and substantial impact on mortality and long-term outcomes. Pasini et al. [6] emphasized the importance of comprehensive AKI monitoring using neonatal-modified KDIGO criteria, which include both serum creatinine changes and urine output. This approach ensures accurate identification of AKI cases, including those associated with fluid overload, which might otherwise be missed. The study also highlights the complex interplay of risk factors for AKI and underscores the need for further research to clarify these relationships and improve clinical management. Finally, addressing the long-term implications of AKI in neonates is crucial. Longitudinal studies are needed to evaluate the progression of renal and non-renal outcomes in affected individuals. By expanding our understanding of the AKI risk factors, diagnostic criteria, and long-term effects, clinicians can develop more effective strategies to mitigate the burden of AKI and improve outcomes in vulnerable populations.