Derivation and evaluation of baseline creatinine equations for hospitalized children and adolescents: the AKI baseline creatinine equation

Background Acute kidney injury (AKI) definitions incorporate baseline creatinine (Cr b ) values, but Cr b are frequently unknown in pediatrics. Our primary aim was to derive and validate a novel AKI Baseline Creatinine (ABC) estimation equation and compare it to existing methods of estimating Cr b values. Methods We conducted a single-center retrospective analysis of pediatric patients (0–25 years) admitted from 2012 to 2019. Included patients required at least one outpatient Cr b prior to hospitalization (gold standard). Novel equations were developed with demographic and initial creatinine data. Existing methods included back-calculating Cr b based on Schwartz, Full Age Spectrum (FAS), and CKiD-under-25 (U25) equations. To determine an optimal equation, we compared novel and existing equations to the gold standard. Results The optimal simplified equation (ABC) included only age and had R 2 = 59.9% and 73.2% of values within 30% of true Cr b . The precision increased significantly when the equation included age and minimum creatinine within initial 72 h (ABC-cr): R 2 = 75.4% and 86.5% of values within 30% of true Cr b . The best performing existing equation was the age-based FAS, which had R 2 = 61.0% and 78.0% of values within 30% of true Cr b . All other existing equations performed worse, some methods as low as 52.6% within 30% of true Cr b . Conclusions The newly derived ABC equation is simple, and the ABC-cr equation can more accurately estimate Cr b by ≥ 25% compared to previous methods. The potential applicability of these equations is vast, including faster recognition of AKI on initial patient contact and improved standardization of pediatric AKI definitions, enhancing health services research. Graphical abstract A higher resolution version of the Graphical abstract is available as Supplementary information .