Evaluation of renal function in potential living kidney donors

Most transplant centers in the United States, including our own, use creatinine clearance (Ccr) to estimate glomerular filtration rate (GFR) in potential living kidney donors. The purpose of this study was to evaluate our experience with estimation of donor GFR by Ccr and to explore other potential strategies for evaluation of renal function in donors.

Potential donors performed one to three outpatient urine collections for Ccr measurement. Those with low or inconsistent results underwent measurement of GFR by a radionuclide method not dependent upon urine collection (rGFR). The ability to determine adequacy of urine volume by creatinine excretion rate (UVcr) was examined. GFR was also predicted from serum creatinine (Scr) by using two prediction equations [Cockcroft-Gault and that from the Modification of Diet in Renal Disease Study (MDRD)]. The effect of indexing GFR by height, as opposed to body surface area (BSA) was explored.

Over a 5-year period, 22 potential donors (approximately 10% of total evaluated) had inconsistent or low Ccr. Most had normal rGFR and, presumably, undercollected their urine. However, several female donors had truly low GFR by rGFR. The accuracy of Ccr (compared with rGFR) was not predicted by UVcr in a clinically useful way. The prediction equations did not have sufficient accuracy or precision to replace rGFR in this population. Indexing GFR estimates by BSA introduced a bias toward lower values in females; this was largely overcome by indexing GFR by height.

Evaluation of GFR in potential living donors by Ccr is not very useful. A more promising strategy could be developed predicting GFR from Scr and indexing the results by height rather than BSA. The optimum method for evaluation of renal function in kidney donors deserves further study.