Creatinine at Birth Correlates with Gestational Age and Birth Weight: Another Factor of the Imbroglio in Early Neonatal Life

Abstract

<b><i>Background:</i></b> Serum creatinine (S_cr) in early neonatal life (first week of life) displays extensive variability; hence, a better understanding is needed to use S_cr as a diagnostic biomarker for acute kidney injury (AKI). <b><i>Objective:</i></b> The objective of this study was to explore S_cr trends and its covariates in early neonatal life. <b><i>Methods:</i></b> Analysis of a rich, pooled S_cr dataset (enzymatic assay) of 4,509 S_cr observations in 1,181 neonates in the first week of life with birth weight, gestational age (GA), and postnatal age as covariates was conducted. Descriptive data were summarized as median and range. The Spearman rank correlation test was used to examine S_cr, while the Mann-Whitney U test was used to determine the differences between the different GA (≤32, 33–36, or ≥37 weeks) categories. <b><i>Results:</i></b> The median S_cr at delivery was 55.7 (range 28.3–194.5) µmol/L, correlating with birth weight (<i>r</i> = 0.088) or GA (<i>r</i> = 0.183) for the full dataset. At birth, the median S_cr was highest in term (≥37-week) neonates. In early neonatal life (median S_cr values), there was a gradual increase to attain a peak S_cr by day 2–3, highest and most delayed in neonates ≤32 weeks GA. This is followed by a blunted decrease when ≤32-week neonates were compared to those of 33–36 or ≥37 weeks GA. <b><i>Conclusions:</i></b> The S_cr pattern in early neonatal life is complex, with the highest S_cr at birth in full-term neonates, while those ≤32 weeks GA displayed the highest and delayed peak S_cr with a subsequent blunted decrease. Knowledge of these patterns is crucial to explore the utility of S_cr as an AKI biomarker.