Estimating baseline kidney function in hospitalized adults with acute kidney injury

AIM: Baseline serum creatinine values are required to diagnose acute kidney injury but are often unavailable. We evaluated four conventional equations to estimate creatinine. We then developed and validated a new equation corrected by age and gender. METHODS: We retrospectively examined adults who, at first hospital admission, had available baseline creatinine data and developed acute kidney injury ≥24 h after admission. We split the study population: 50% (derivation) to develop a new linear equation and 50% (validation) to compare against conventional equations for bias, precision, and accuracy. We stratified analyses by age and gender. RESULTS: We studied 3139 hospitalized adults (58% male, median age 71). Conventional equations performed poorly in bias and accuracy in patients aged <60 or ≥75 (68% of the study population). The new linear equation had less bias and more accuracy. There were no clinically significant differences in precision. The median (95% confidence interval) difference in creatinine values estimated via the new equation minus measured baselines was 0.9 (−3.0, 5.9) and −0.5 (−7.0, 3.7) μmol/L in female patients 18–60 and 75–100, and −1.5 (−4.2, 2.2) and −7.8 (−12.7, −3.6) μmol/L in male patients 18–60 and 75–100, respectively. The new equation improved reclassification of KDIGO AKI stages compared to the MDRD II equation by 5.0%. CONCLUSION: Equations adjusted for age and gender are less biased and more accurate than unadjusted equations. Our new equation performed well in terms of bias, precision, accuracy, and reclassification.