Improving AKI Diagnosis: Estimating Baseline Serum Creatinine Using Kidney Volume Regression Equation

Background: Diagnosing acute kidney injury (AKI) relies on baseline serum creatinine (Cr) levels, which are often unavailable. As shown in Figure A, our study aimed to create a regression equation linking kidney volume to function in kidney donors and chronic kidney disease patients, and also sought to estimate baseline Cr in minimal change disease (MCD) patients, which is a common AKI-predisposing condition. Methods: Kidney donors and patients with chronic kidney disease (CKD) were selected for our study (n = 119, 40% donors, mean age 60 years, 50% male), and randomly divided into derivation and validation groups (Figure B). An equation based on kidney volume (KV) was developed in the derivation group and validated in the validation group. We also estimated baseline Cr in MCD patients (n = 43, mean age 45 years, 61% male) using the KV-based equation and compared with their 6-month post-MCD onset Cr values. Results: The created equation for the estimated glomerular filtration rate (eGFR) was as follows: eGFR (mL/min/1.73m^2) = 0.38 x KV (cm^3) + (-0.40) x age (years) + (-2.9) x male sex + (-13) x hypertension + (-14) x diabetes + (-0.21) x height (cm) + 82 (intercept). In the validation group, the eGFR and estimated Cr values correlated well with the measured values (r = 0.46, p = 0.01 and r = 0.51, p = 0.004, respectively). In the MCD group, the baseline Cr values were significantly correlated with the estimated baseline Cr values (r = 0.52, p <0.001), effectively diagnosing AKI (kappa = 0.76, p <0.001). Conclusion: The regression equation including KV established in the present study holds promise for estimating baseline Cr values and diagnosing AKI in patients with MCD. Further validation in diverse populations with AKI is necessary.