Donor age, quality of the graft, and the size/weight of the donated kidney are factors that may affect subsequent transplant outcomes. Morphological renal measurements may be reliably obtained using 3D reconstructions of CT angiograms (CT-V) yet no metric exists to objectively describe the quality of the donated tissue. We propose creating a new term: “Renal Efficiency” (RE) to fill this void. This term will be defined as the creatinine clearance that is produced per cubic cm (cc) of donated kidney tissue.

Under IRB approval, we retrospectively reviewed data from living kidney donors who donated over 5 years at our center and abstracted demographic and clinical data, pre-donation 24hr timed creatinine clearance measurements (mCrCl) [validated for adequacy of collections] and CT-V. RE was generated by dividing mCrCl (ml/min) by kidney volume (cc). A natural log transformation was employed to reduce variance in data analysis. Natural log transformed renal efficiency was linearly regressed on patient demographics and clinical characteristics. Regression coefficients were back transformed to the original renal efficiency units of ml/min (mCrCl) per cc of renal tissue (CT-V).

312 cases were reviewed. The average total CT-V (combined right and left kidneys) was 349.91 ml (sd 65.96). The average mCrCl was 123.21 ml/min (sd 27.34). We previously described the strong correlation that exists between (mCrCl) and (CT-V) (Pearson Correlation: 0.65, p<0.001).The average RE was 0.35 ml/min (clearance) per cc (renal tissue) [Std Error: 0.003, 95% CI: 0.343 – 0.357]. Both univariable (unadjusted) and multivariable (adjusted) linear regression modeling showed significant correlations with patient age and race. For every ten year increase in age we noted a renal efficiency decreases of 4% (ratio = 0.96, 95% CI: 0.95 – 0.98, p < 0.001). For race renal efficiency increases 10% (ratio = 1.10, 95% CI: 1.04 – 1.16, p = 0.001) in non-whites as compared to whites. This is interesting as some groups (e.g. African Americans) have higher rates of CKD; and may either reflect an associated mechanism, or bias in the patients selected for donation.

Our data show that there is variability in the quality of donated renal tissue. We believe that the term “Renal Efficiency” objectively describes this variability. In further studies we hope to show that combined measurements of renal efficiency and renal volume may predict renal function in kidney transplant recipients.

CITATION INFORMATION: Diez A, Rima K, Von Visger J, Nori U, Pesavento T, Rajab A, Henry M, Pelletier R. Renal Efficiency: A New Metric for Evaluating Kidneys in Living Donors. Am J Transplant. 2016;16 (suppl 3).

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