Expanded criteria donor kidneys (ECD) have the potential to greatly increase the number of kidneys available for transplantation; however utilization is limited by poorer outcomes [1] [2] [3] [4] [5] . One strategy to improve outcomes and secondarily utilization is improved matching of kidneys based on recipient factors such as surface area [6, 7] , kidney graft size to recipient weight [8] and kidney weight to recipient weight [9, 10] . Recently our group developed the creatinine clearance

more »

... h ratio (CCMR) as an improved matching technique. The CCMR is calculated using a manipulation of the Cockcroft-Gault equation estimating the creatinine clearance required by the recipient at a serum creatinine level of 1.0 thereby producing an estimated value for an individual's creatinine production and in intellectual shorthand, "nephron need" [11, 12] . We simply asked; "how much Creatinine clearance would a potential recipient require to achieve a post-transplant serum creatinine of 1.0, " and then created a variable utilizing Cockcroft-Gault estimated donor creatinine clearance from known donor variables. Simplification results in the equation below. CCMR = (140-age recepient )*(Mass in Kg recepient )*(0.85 if female)/ (140-age donor )*(Wt in Kg donor )*(0.85 if female)/(Serum Cr mg/dL donor ) Put simply, a high creatinine producer (numerator) matched to a donor kidney with a lower estimated creatinine clearance (denominator) produces a higher value. Conversely, a low creatinine producer (numerator) matched to a kidney with a higher estimated clearance (denominator) results in a lower value. Briefly summarizing the findings of our study of 25,640 ECD kidney transplants: 1) multivariate analysis demonstrated higher CCMR was associated with increased graft failure and odds of requiring dialysis within the first week (comparing highest ratio quintile versus lowest ratio quintile: HR 1.43, p<0.001; OR 2.08, p<0.001) and 2) CCMR was found to be superior in prediction and discrimination ability as compared to donor creatinine clearance, recipient/donor age ratio, and recipient/donor weight ratio. To compare the utility between CCMR and other predictive strategies utilized in ECD transplantation -KDRI, weight ratio, age ratio, and recipient and donor creatinine clearances. CCMR, weight ratio, and recipient clearance were found to be statistically significant for both outcomes, whereas KDRI and age ratio were only significant for predicting graft failure. Surprisingly, estimated donor clearance alone was not found to be statistically significant in any model. These results suggest that ECD kidneys have improved short-and