Renal function of the remaining kidney in living donors appears to improve for many years but then shows signs of slight deterioration long term, according to a new Swedish study.

Ingela Fehrman-Ekholm, MD, of the Transplant Institute at Sahlgrenska University Hospital in Gothenburg, Sweden, and colleagues examined long-term donor outcomes and risks following living donor kidney transplantation. The researchers looked at 573 kidney donors who had a mean age of 47 years at the time of donation.  The mean time since donation was 14 years.

The mean estimated glomerular filtration rate (eGFR) decreased with age and increased with time since donation, the researchers reported online in Nephrology Dialysis Transplantation. The findings suggest that for 30-year old donors, the median eGFR typically increases during the first 17 years and then remains constant for approximately eight years, and then slowly declines thereafter. For a 50-year old donor, the median eGFR is expected to increase for approximately 15 years and then to “enter a phase of slight progressive decline,” the authors wrote.

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In the current investigation, the researchers found that 23% of the donors were on antihypertensive medications and an additional 22% of the donors suffered from undiagnosed hypertension (blood pressure greater than 140/90 mm Hg). The researchers observed an increase in microalbuminuria over time since donation. They presume this is due to the hyperfiltration effect.

The investigators also cautioned that their study covers a period of 40 years and so there is a possibility that changes in kidney donor selection criteria may have influenced the results.