Impact of errors of creatinine and cystatin C equations in the selection of living kidney donors

Abstract

Background Reliable determination of glomerular filtration rate (GFR) is crucial in the evaluation of living kidney donors. Although some guidelines recommend the use of measured GFR (mGFR), many centres still rely on estimated GFR (eGFR) obtained through equations or 24-h creatinine clearance. However, eGFR is neither accurate nor precise in reflecting real renal function. We analysed the impact of eGFR errors on evaluation and decision making regarding potential donors. Methods We evaluated 103 consecutive living donors who underwent mGFR via iohexol plasma clearance and eGFR by 51 creatinine- and/or cystatin C–based equations. The cut-off for living donation in our centre is GFR > 80 mL/min for donors >35 years of age or 90 mL/min for those <35 years of age. We analysed the misclassification of donors based on the cut-off for donation-based eGFR. Results Ninety-three subjects (90.3%) had mGFR values above (donors) and 10 [9.7% (95% confidence interval 5.4–17)] below (non-donors) the cut-off. In non-donors, most of the equations gave eGFR values above the cut-off, so donation would have been allowed based on eGFR. All non-donors were female with reduced weight, height and body surface. In donors, up to 32 cases showed eGFR below the cut-off, while mGFR was actually higher. Therefore an important number of donors would not have donated based on eGFR alone. Conclusion The misclassification of donors around the cut-off for donation is very common with eGFR, making eGFR unreliable for the evaluation of living kidney donors. Whenever possible, mGFR should be implemented in this setting.

Assessment of kidney function: clinical indications for measured GFR

“…Such a low sensitivity is not acceptable for donor screening, as individuals with a low eGFR for their age are probably at the highest risk of subsequent end-stage kidney disease [ 115 ]. Similarly, a Spanish study showed that in 10% of the cases eGFR was above the cut-off for donation, whereas mGFR was evidently below the threshold [ 116 ]. Furthermore, eGFR contraindicated donation in 20–30% of cases, while mGFR levels were above the cut-off for acceptance for donation.…”

Measurement of glomerular filtration rate using endogenous d-serine clearance in living kidney transplant donors and recipients

“…While this method is widely used for screening of renal function because of its simplicity, it has the limitations in terms of precision [26] . In particular, it is known that there is a relatively large difference from GFR in populations with good renal function [7] , and the use of eGFR alone is not recommended in key clinical situations such as to determine the suitability of living donors for kidney transplantation [27] . C- d Ser may solve this clinical problem.…”

“…Most equations for eGFR show relatively small bias, however, their precisions are not good enough to provide a correct estimation for the individual patient [5] . Endogenous molecules that potentiate the precise assessment of kidney function with small biases is still necessary for important clinical decisions, including drug administration design, transplant donor selection, and CKD stage classification [ 6 , 7 ].…”

PDGFR ‐β and kidney fibrosis

“…Thus, although CKD risk categories are well defined and internationally accepted, they are based on estimated glomerular filtration rate (GFR) and assessment of albuminuria. GFR estimation is notoriously inaccurate, and there is no consensus on the risk associated with GFRbased category G3a, the most common CKD stage (González-Rinne et al, 2019). Additionally, pathological albuminuria is found both in active ongoing glomerular injury and in residual glomerular sclerosis.…”