*Purpose: According to current guidelines, a kidney biopsy is indicated in prospective living kidney donors who present with persistent isolated microscopic hematuria (PIMH) during evaluation, while post-donation risks of PIMH are unclear. Here, we investigated the risks of pre-donation PIMH on post-donation kidney outcomes.

*Methods: We included 858 living kidney donors who underwent at least two urinalyses before donation and had yearly post-donation kidney function (estimated glomerular filtration rate (eGFR), proteinuria (assessed as the protein/creatinine-ratio (PCR)) and systolic blood pressure (SBP) measurements available. The association between pre-donation PIMH (at least two positive measurements with ≥ 1 red blood cell (RBC) per high power field or ≥ 5 RBC per µL) and post-donation kidney function was assessed using generalized linear mixed models.

*Results: Mean age was 52 (11) and median [IQR] follow-up time was 36 [12-70] months. Pre-donation PIMH was present in 78 donors of whom 74% were female, versus 48% female in the non-PIMH group (P<0.001). There was no significant difference in post-donation ln(PCR), eGFR or SBP course between pre-donation PIMH and non-PIMH donors (0.01 and 0.03 increase/year for PIMH donors and non-PIMH donors, respectively; difference P=0.34), eGFR (0.41 and 0.33 increase/year for PIMH donors and non-PIMH donors, respectively; difference P=0.41), or SBP (1.24 and 0.93 increase/year for PIMH donors and non-PIMH donors, respectively; difference P=0.70), even after adjusting for pre-donation age, sex, BMI, pre-donation eGFR, SBP, and ACE inhibitor use.

*Conclusions: We found no increased risk of post-donation proteinuria, higher blood pressure, or eGFR decline in donors with pre-donation PIMH. The need of a pre-donation kidney biopsy in donors with PIMH without other risk factors for kidney disease should be carefully reconsidered.

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