Kidney Function in Living Donors: Understanding Health Versus Disease

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Kidney transplantation is the best available treatment for patients who suffer end-stage renal disease (ESRD). However, the main limitation to universal access to transplantation is organ shortage.

According to the United Network for Organ Sharing (UNOS), approximately 85,000 patients with ESRD are awaiting kidney transplantation in the United States, but only about 16,000 patients were transplanted in 2008.

Therefore, the current demand for kidney transplants is five to six times higher than the number of organs offered annually. The average patient waits four to five years before receiving a deceased-donor organ. While 64 % of the organs came from deceased donors in 2008, the remaining kidneys were donated by living donors.

In fact, more than 90,000 living donors have donated a kidney since 1998, according to UNOS. Living donation not only offers better long-term outcomes but also allows for timed donation, avoiding long waits that are detrimental to recipients.

A common concern of the health-care practitioner as well as the prospective donors and recipients relates to the long-term safety of organ donation.

Fortunately, when a proper evaluation is undertaken to rule out medical and renal abnormalities, the long-term outcomes of former kidney donors suggest that these individuals enjoy a quality of life that is equal to if not better than that of the general population. The rate of renal disease in former donors is also the same as or lower than that observed in the general population.

Nevertheless, a careful pre-donation evaluation with special emphasis on kidney function and a post-donation follow-up are needed to continue to protect this altruistic population.

The classification of kidney disease as defined by the National Kidney Foundation (NKF) is strongly based on the level of kidney function. The current classification states that an individual whose glomerular filtration rate (GFR) is below 60 mL/min/1.73 m2 has kidney disease, irrespective of cause.

This classification does not take into consideration physiologic age- or gender-related decline in kidney function. Anyone with a GFR greater than 80 is usually considered a potential kidney donor irrespective of gender or age. That is, a GFR of 85 would qualify a 25-year-old male and a 60-year-old female equally for kidney donation.

While controversial, application of the NKF guidelines suggests that a former kidney donor whose post-donation estimated GFR falls below the cutoff value of 60 (by virtue of having donated 50% of his or her kidney mass) would qualify as having kidney disease. (Approximately 20%-30% of kidney function is regained as part of the compensation achieved by the remaining kidney following donation.)

Because GFR has such an important role in both kidney disease and kidney donation, understanding how age and gender can affect that parameter's normal range is crucial. Recently, we reported on the kidney function measurements obtained as part of the pre-donation evaluation at Cleveland Clinic from 1972 to 2005.

Based on values derived from more than 1,000 former kidney donors, we clearly showed that normal values of GFR decline as we age. Therefore, using fixed cut-off values to define kidney disease or normality (in terms of allowing donation) may put some populations at risk for having the health status of their kidneys misclassified.

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