Correlating Kidney Failure Risk Equation and Kidney Biopsy Chronicity Score as Kidney Failure Predicting Tools

Background: Progression to kidney failure (KF) may be estimated by the Kidney Failure Risk Equation (KFRE), based on age, gender, eGFR and uACR. Kidney biopsy (KB) chronicity score (KBCS), which evaluates the degree of glomerulosclerosis, interstitial fibrosis, tubular atrophy and arteriosclerosis, also predicts progression to KF. We aimed to compare and validate both scores in outcome prediction in a retrospective single-center cohort study. Methods: Patients who underwent KB from 2017 to 2022 were analyzed. Exclusion criteria were: acute kidney injury, rapidly progressive glomerulonephritis; kidney replacement therapy (KRT) dependence up to 90 days after KB; insufficient histological sample; follow up <2years or death. Results: From a total of 235 patients, 121 patients were included: 55% (n=68) were male, with a median age of 53 years (IQR 43-65); 78% (n=94) were hypertensive, 63% (n=75) had overweight and 35% (n=42) diabetes. At the time of KB, median eGFR was 43ml/min/1.73m2 (IQR 25-68); median uACR was 2469 mg/g (IQR 964-4490); 74% (n=89) had microscopic hematuria. Median KFRE at 2 years was 2.6% (IQR 0.2-19.3) and at 5 years 9.6% (IQR 0.7-56.5). Median KBCS was 6 (IQR 3-8). At 2 and 5 years of follow-up, 23% (n=28) and 9% (n=11) of patients reached KF, respectively. At 2 and 5 years, KBCS correlated with progression to KF (r=0.543 and r=0.613, p<0.001) as well as KFRE (r=0.553, and r=0.542, p<0.001). Both KBCS and KFRE correlated with each other at 2 and 5 years (r=0.622 and r=0.613, p<0.001). In the subgroup of patients with eGFR>60ml/min/1.73m2 (n=42, 35%) at the time of biopsy, the scores KFRE and KBCS were unable to predict progression to KF (p=0.656 and p=0.084, respectively). Conclusion: In our cohort, there was a positive correlation between KFRE and KBCS, irrespectively of eGFR. Overall, both KFRE and KBCS were able to estimate progression to KF at 2 and 5 years, showing the usefulness of these tools in clinical practice and in providing timely guidance to patients regarding KRT. In the subgroup of patients with eGFR>60ml/min/1.73m2, however, neither KFRE or KBCS associated with KF, revealing a gap in clinical, laboratory and histological markers that can better define risk progression in this population.