Abstract and Introduction
Abstract
Over the past two decades, live kidney donation by older individuals (≥55 years) has become more common. Given the strong associations of older age with cardiovascular disease (CVD), nephrectomy could make older donors vulnerable to death and cardiovascular events. We performed a cohort study among older live kidney donors who were matched to healthy older individuals in the Health and Retirement Study. The primary outcome was mortality ascertained through national death registries. Secondary outcomes ascertained among pairs with Medicare coverage included death or CVD ascertained through Medicare claims data. During the period from 1996 to 2006, there were 5717 older donors in the United States. We matched 3368 donors 1:1 to older healthy nondonors. Among donors and matched pairs, the mean age was 59 years; 41% were male and 7% were black race. In median follow-up of 7.8 years, mortality was not different between donors and matched pairs (p = 0.21). Among donors with Medicare, the combined outcome of death/CVD (p = 0.70) was also not different between donors and nondonors. In summary, carefully selected older kidney donors do not face a higher risk of death or CVD. These findings should be provided to older individuals considering live kidney donation.
Introduction
The lower GFR associated with aging has raised concerns about the safety of living kidney donation by older adults. Further, given the strong associations between both older age and chronic kidney disease with cardiovascular disease (CVD), older live kidney donors could have an augmented risk of CVD attributable to nephrectomy. Despite these concerns, older individuals (≥55 years of age) represent a rapidly growing segment of live kidney donors and two consecutive surveys of transplant center policies suggest that centers are increasingly willing to accept older kidney donors.
Epidemiological and physiological studies have demonstrated the loss of kidney function associated with older age, although this loss varies widely among individuals. The National Health and Nutrition Examination Survey (NHANES) showed that the prevalence of stages 3–4 chronic kidney disease increased from 0.7% in the 20- to 39-year-age group to 37.8% among individuals >70 years in the general population. Directly measured hemodynamics and clearance reveal that healthy older individuals have lower renal plasma flow, increased vascular resistance and higher filtration fraction compared to their younger counterparts. Pathological examination of kidneys from older patients shows nephrosclerosis, loss of glomeruli and loss of renal mass.
For older donors, diminished filtration function at baseline might impair the ability of the remnant kidney to perform adaptive hyperfiltration and promote progressive kidney disease or comorbidities such as CVD. On the other hand, given that older donors have fewer expected years of survival compared to younger donors, older donors will experience a briefer period with a single kidney, which might reduce the opportunity for adverse consequences of nephrectomy.
Prior epidemiological studies have been limited by the small numbers of older live kidney donors, single-center populations, short-term follow-up or a lack of CVD outcomes. In a single-center study of older live kidney donors in the Netherlands, older age was associated with lower GFR both predonation and postdonation, with lower estimated GFR and lesser augmentation of GFR in response to dopamine. In three related studies using US registry data, older kidney donors had similar rates of mortality but higher rates of end-stage renal disease (ESRD) compared to healthy nondonors identified through NHANES. However, the health of the nondonor comparators was determined during an earlier period than when the donors underwent nephrectomy, creating the possibility of a less-healthy comparison group. Canadian studies of CVD outcomes among live kidney donors had a small percentage of older donors. Therefore, the primary aim of this study was to compare rates of death and CVD in a large cohort of older live kidney donors to contemporary, healthy matched nondonors.