Adequacy of decision-making based on each kidney function estimation method for Japanese living kidney donor candidates: a retrospective observational study

Abstract

BackgroundLiving kidney transplantation comprises the majority of kidney transplantations in Japan. Living kidney donors should be assured of their own health. Therefore, Japanese guidelines define the criterion of kidney function for living donors. Glomerular filtration rates (GFR) ≥ 70 mL/min/1.73 m2 are required for marginal donors. The guidelines require that GFRs of donors be measured by the inulin (In) clearance method (CIn) or the radioisotope method, but these methods can be substituted with the creatinine (Cr) clearance method (CCr). Methods for estimating kidney function are susceptible to error, and decision-making regarding donor eligibility could be affected by the estimation method used. We investigated the adequacy of decision-making based on kidney function estimation methods used in Japanese living kidney donor candidates by comparing CCr or estimated GFR (eGFR), calculated by several equations, and CIn as measured GFR (mGFR).MethodsIn total, 210 people, including 36 actual kidney donor candidates, who had both CIn and CCr measured at Shinshu University Hospital from April 2011 to April 2015, were included. Cr and cystatin C (Cys) levels measured at the same time were used to calculate eGFR (eGFRCr and sGFRCys, respectively). We evaluated the concordance rates of cases whose GFR levels were ≥ 70 mL/min/1.73 m2 in this study and assumed that they were living kidney donor candidates. Only kidney donor candidates underwent an additional sensitivity analysis.ResultsMedian CIn and CCr were 55.5 mL/min/1.73 m2 and 68.0 mL/min/1.73 m2, respectively. CCr had the highest tendency to overestimate kidney function. Some participants were incorrectly evaluated as adequate using CCr, despite their mGFR being inadequate for living kidney donors according to the guidelines. These results were independent of sex or actual living kidney donor candidates. The average of eGFRCr and eGFRCys was well correlated with CIn.ConclusionsKidney function estimated by CCr is not equal to the mGFR. When using CCr as a kidney function estimation method to determine the adequacy of a living kidney donor, it should be noted that CCr overestimates kidney function. In evaluating adequacy for a marginal donor, GFR estimated by CIn should be assessed.