Development of an estimating equation for the baseline creatinine level in critically ill pediatric patients

Background: The current diagnostic criteria for acute kidney injury mainly rely on baseline serum creatinine (SCr-base). However, this information is frequently missing or unavailable for a significant number of hospitalized patients. In this study, we developed an estimating equation (EE) for SCr-base and validated its performance in critically ill pediatric patients. Methods: This single-center retrospective study included patients admitted to the pediatric intensive care unit (PICU) at a tertiary care children’s hospital between January 2016 and July 2020. These patients had a measured SCr-base (mSCr-base) within 3 months prior to admission and initial SCr value at PICU admission (SCr-adm). The patients were divided by admission date into a derivation cohort and a validation cohort for the development and validation of the EE. Results: In total, 761 children were included in the study (605 in the derivation cohort and 156 in the validation cohort). We employed linear regression analysis to develop the following EE: eSCr-base=0.159+(–0.031)×sex+(0.355×SCr-adm)+(0.006×weight for height z-score). Compared to other imputation methods for SCr-base, such as SCr-adm and SCr-base determined by back-calculation with an assumed estimated glomerular filtration rate of 75 mL/min/1.73 m 2 (SCr-eGFR75), eSCr-base demonstrated higher agreement with mSCr-base, exhibiting less bias (0.005) and narrower limits of agreement (LOA) interval (0.506). Conclusion: eSCr-base calculated through an EE showed better agreement with mSCr-base, with less bias and a smaller LOA interval than other currently used methods (SCr-adm and SCr-eGFR75). Further large-scale studies are necessary for validation and widespread adoption.