Outcomes of living kidney donors with medullary sponge kidney

BACKGROUND Patients with medullary sponge kidney (MSK) commonly encounter recurrent nephrolithiasis. The existing knowledge on safety of donors with MSK has not been studied. METHODS We conducted a retrospective cohort study at a tertiary referral hospital to assess the outcomes of living kidney donors with MSK. All adults with MSK (N = 26) who underwent nephrectomy as living kidney donors between January 2000 and September 2014 were included. Non-donors with MSK (N = 78) were randomly selected by matching the year of birth and the comorbidity score with a ratio of 1:3 for comparison. RESULTS The incident rates of symptomatic stone were 0.7, 0.4 and 4.9 events/100 patient-years in donors, recipients and non-donors, respectively. After adjusting for history of kidney stones and baseline estimated glomerular filtration rate (eGFR), the kidney stone-related event was significantly lower in donors than in non-donors (hazard ratio 0.14; 95% confidence interval 0.01-0.66). One recipient of MSK living donor had symptomatic stone at median follow-up time of 8.4 years (interquartile range 5.6-12.4 years). None of MSK donors had hypercalciuria, hypocitraturia or hyperoxaluria prior to kidney donation. At 5 years after the index surgery date, there was no significant difference in eGFR between donors and non-donors (76.1 versus 70.9 mL/min/1.73 m2, P = 0.12). CONCLUSIONS These findings are reassuring for the safety of MSK kidney donors with normal kidney function, low kidney stone risk and no significant comorbidity.