Article of the Month - Feb 2021

Trends and racial disparities for acute kidney injury in premature infants: the US national database

Pediatr Nephrol . 2021 Feb 22. doi: 10.1007/s00467-021-04998-w

Elgendy MM, Othman HF, Younis M, Puthuraya S, Matar RB, and Aly H

Reviewed by Jennifer Jetton

What is the purpose of the study?

The stated aims of the study are 1) to assess the prevalence of AKI in very low birth weight (VLBW) infants, 2) to determine the rate of mortality and associated morbidities with AKI in this population, and 3) to examine the frequency trends for AKI during the years 2000-2017 using a large national database.

What was the study design?

Cross-sectional study utilizing the National Inpatient Sample (NIS) dataset for years 2000-2017. Approximately 1000 hospitals in the US are included in this dataset. The NIS is the “largest publicly available all-payer inpatient care database in the US, containing data on > 7 million hospital stays”  and is part of the Healthcare Cost and Utilization Project (HCUP) of the Agency for Healthcare Research and Quality (AHRQ) (www.hcup-us.ahrq.gov/db/nation/nis/nisdbdocumentation.jsp).

What were the characteristics of the sample?

This study cohort included premature (gestational age < 32 weeks) and VLBW babies < 1500 g. Infants were divided into two birthweight categories < 1000g and 1000-1499g. Final sample included 1,311,681 premature infants. AKI diagnosis was determined by presence of ICD-9 and 10 codes. Information on comorbidities (e.g., IVH, NEC, ROP) was also extracted. Patients with chromosomal abnormalities, congenital anomalies of urinary system, major congenital heart disease, and death in the first 72h of life were excluded (468,169 babies). The dataset included a diverse sample from the perspective of race, payor mix, region, type of hospital (e.g., urban teaching, rural), and gestational age and birthweight range.

What are the results?

AKI diagnosis was made in 1.5% of the babies in this sample (n=19,603). The majority of the babies with AKI diagnosis were <1000g (74.3%) and < 28 weeks GA (63.9%).  AKI prevalence was higher in the smallest babies: 8.1% in BW <500 g compared with 4.1% with BW 500-1000g and 0.64% in BW 1000-1499. Preterm infants with AKI had higher mortality (35.1% vs 3%), hospital length of stay, and hospital cost compared with controls. The within-race prevalence of AKI was higher in Black (1.78%, OR = 1.27, CI 1.23-1.32, p < 0.001), Hispanic (1.68%, OR = 1.21, CI 1.16-1.26, p < 0.001) and Native American (1.61%) babies than in White (1.39%) babies and lowest in Asian or Pacific Islander babies (1.18%). Babies in the “other” category had an AKI prevalence 1.79%. White race was associated with decreased mortality in both univariate and multivariate regression analysis (OR 0.77, CI 0.75-0.78, p < 0.001 and aOR 0.90, CI 0.88-0.92, p < 0.001).

Interestingly, the trend of AKI frequency increased significantly over the years in the overall population (from 1.3 to 1.9%, Z score = 4.33, p < 0.001)) and particularly in the < 1000g babies (from 2.5 to 5.9%, Z score = 11.75, p < 0.001).

What are the implications?

This large nationwide dataset demonstrates again the impact of AKI on outcomes overall in premature and VLBW babies – especially in terms of mortality, hospital length of stay, and hospital cost (babies with AKI have hospital costs about 3 times higher than babies without AKI). The prevalence of AKI 1.5% is much lower than in other single-center studies and in the AWAKEN cohort, but not surprising given that the diagnosis was based on ICD-9&10 codes and not by review of creatinine and urine output data (side note, we also know from our experience that frequency of kidney function monitoring and hence the diagnosis of AKI varies widely across centers. There is also data supporting discrepancies between the diagnosis of AKI by review of serum creatinine/UOP and by ICD-9/10 coding). The authors consider that the increase in frequency of AKI over the years may be due to advances in care, particularly in the area of successful resuscitation of the smallest babies. In addition, the standardization of neonatal AKI definitions may be leading to greater awareness and recognition of neonatal AKI (another side note – it will be interesting to look at this data again when information through 2022 is available to see how these trends change – are we improving in terms of neonatal AKI recognition – or better still, does greater awareness result in changes in clinical care that reduce AKI frequency?).

Importantly, this study is the first to examine the intersection of race and neonatal AKI and highlight a potential racial disparity. This compelling data leads to many questions for future study including whether this risk is related to modifiable factors such as quality of prenatal care or access to care in general that lead to prematurity and critical illness, is attributable to inherited/genetic AKI risk factors, or some combination. One Med Twitter user also made the important point that the combination of AKI and prematurity/decreased nephron mass increases the risk for CKD, and that our ability to identify and address issues of health care equity and inequities where they exist has lifetime implications for these patients.