Renal transplantation is the treatment of choice for end stage renal failure as it results in improved patient survival and quality of life as compared to dialysis. Accurate study of renal function and morphology for potential kidney donors is essential to ensure that no harm from donation is incurred. The gold standard to assess renal function is the measurement of Glomerular filtration rate (GFR). However, GFR is often estimated from serum creatinine (SCr), serum cystatin C (SCys), or creatinine clearance (CCr), Otherwise, GFR is predicted using formulas based on SCr or SCys. Ultrasound scanning evaluates morphology and dimensions of kidneys.
Aim of this work was to evaluate the possibility to obtain, by means of renal sonography, information useful to evaluate renal function in the setting of living kidney donation.
Preliminary data obtained from chronic kidney disease (CKD) patients indicated that information useful to evaluate renal function can be obtained by means of renal echography. On the basis of these results we planned further studies first in kidney donors after donation and in renal transplant recipients to evaluate the relationship among renal dimensions and renal function and we found that the correlation of kidney length with GFR was greater than that of S Cr or S Cys, and similar to that of Cockcroft–Gault formula (CG-CCr) or the abbreviated Modification of Diet in Renal Disease formula (MDRD) – GFR. Accuracy of kidney length as an indicator of GFR impairment was not statistically different from laboratory tests. Only in donors did CG-CCr show better accuracy. The second study in potential donors to assess the accuracy of the tests employed to estimate GFR and we found that the correlation with GFR was statistically significant for SCys and for all estimates, but not for SCr. CCr showed a poor agreement with GFR, with a large range of agreement and a marked and significant overestimation of GFR (33.8 mL/min). The accuracy of CG-CCr and MDRD-GFR as indicators of a GFR < 80 mL/min was better than that of Cys-GFR and CCr. However, their mean prediction errors versus GFR were relevant. Renal dimensions, particularly renal volume, showed a good correlation with GFR. The correlation was higher than that of all prediction equations. Then, we performed a last study to evaluate the possibility to predict GFR from echograpohic renal dimensions in potential kidney donors and we found that The estimates of GFR obtained from renal volumes resulted more closely correlated with measured GFR than CG-CCr, MDRD-GFR, and Cys-GFR. Their mean difference with measured GFR was null. GFR estimated from renal volumes had also a better agreement with measured GFR and a lower prediction error versus GFR than the other prediction formulas (18.3 VS 22-34 mL/min). Finally, GFR values predicted from renal volumes were quite accurate as indicators of GFR < 80 mL/min. in conclusion until valid alternatives have been proposed and validated; the reference method for the direct measurement of GFR remains the only accurate method to evaluate renal function in potential living kidney donors. Renal sonography is useful complement in donor screening, providing not only morphologic but also functional information. In particular, from the measurement of renal volumes, it is possible to estimate GFR more accurately and with a lower prediction error than using formulas based on SCr and SCys. However, the prediction error remains quite high.