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) mu mol/L in female patients 18-60 and 75-100, and -1.5 (-4.2, 2.2) and -7.8 (-12.7, -3.6) mu mol/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.