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Chronic kidney Disease (CKD) and Acute Kidney injury (AKI) represent two of the major post-operative long-term complications in patients who undergo radical nephrectomy (RN) for the presence of a renal mass. In daily clinical practice, an accurate assessment of renal function is of paramount importance in this category of patients to reduce the incidence of such complications. In fact, the clinical management of oncological solitary kidney depends mostly on the values of glomerular filtration rate (GFR). the most used technique to measure GFR is represented by the estimated GFR (eGFR) which harbours a significant error in comparison to gold standards (mGFR). Aim of this study was to determine the extent of the error of eGFR compared to the mGFR in onco-nephrological patients, with a particular focus on the solitary kidney (SK).
A total consecutive cohort of 150 nephrectomized patients (pts) enrolled in a single tertiary institution between 2018-2023 was collected in order to compare the most used eGFR formulas used by physicians (Cockroft-Gault, MDRD, CKD-EPI, CKD-EPI based on serum creatinine and/or serum cystatin and new eGFR equation based on creatinine and cystatin without race adjustement) With the most wide spread mGFR method (Iohexol Plasma Clearance). The mGFR techniques together with the serum creatinine/cystatin measurement were performed after 12 months from the operation in order to consider a steady state for the chronic renal function. All clinical variables were reported for each pts. CKD classification was defined accorded to K-DIGO 2012 guidelines. The agreement between eGFR and mGFR was evaluated using bias (as median of difference), precision (ad interquartile range od difference-IQR) accuracy (as P30) and total deviation index (TDI). The differences between cohorts were evaluated with Fisher’s exact test and Chi-squared test for ordinal characteristics and Wilcoxon rank sum test for continuous variables. Data analysis was performed using programming language R and Python.
Clinical data were as follows: median age 66(IQR 27.66), M/F ratio 4.48, median BMI 24.6 (IQR: 0.003, 24.6). 51,3% of patients had hypertension, 10.4% were diabetics. The median creatinine level in the overall population was 1.49 mg/dL (IQR:0,8, 1.49), the median cystatin level was 1.33 mg/dL (IQR: 0.55, 1.33). based on iohexol plasma clearance, 0,87% patients were classified in CKD in stage 1, 17.39% in stage 2, 39.13% in stage 3a, 25.22% in stage 3b, 16.52% in stage 4 and 0.87% in stage 5. Surprisingly, a non-negligible error was reported in each CKD class with a huge discrepancy between the eGFR formulas and the gold standard method (Figure 1 and 2), suggesting the pivotal role of mGFR in the clinical decision making algorithm for nephrectomized patients.
In daily clinical practice and appropriate nephrological tailored follow up based on mGFR is mandatory for RN patients with a solitary kidney. In fact, a simple renal evaluation using eGFR can only increase the risk of clinical errors, sometimes underestimating and sometimes overestimating the real renal function with important medical consequences.