Aging in Kidney Disease: Key Issues and Gaps in Knowledge

In the 1970s, the Baltimore Longitudinal Study of Aging (BLSA) was a longitudinal study of healthy adults with a goal to understand the changes that occur with age. Kidney function was assessed by creatinine clearance collected in a general clinical research center and individuals were examined every 12 to 18 months. With an increase in age, there was a decline in clearance, with little change in serum creatinine.1 The latter was because of a decrease in creatinine generation that was in turn caused by a decrease in muscle mass with age. Although individuals with treated hypertension were excluded from the studies of kidney function, BLSA did not exclude all hypertensives. Subsequent analyses reported an age-related decline when those with a mean arterial pressure >107 were excluded, but this would include individuals with isolated systolic hypertension (eg, a person with a blood pressure of 160/80).2 As isolated systolic hypertension occurs more commonly with an increase in age, it is most likely that many of the older individuals included in the study would be considered hypertensive, if the study were repeated today.

This does not mean that there are no age-related physiologic changes and that kidney function does not decline with age. However, it is important to distinguish the age-related physiologic changes from the decline in kidney function caused by disease. Older individuals often have multiple chronic diseases (multimorbidity)3, 4 and these contribute to age-related diseases. The prevalence of chronic kidney disease (CKD) is greatest in older individuals,5 and those aged 65 also have the highest incidence of end-stage renal disease.6 Focusing on the diseases contributing to decline, rather than on whether the decline is inevitable with age, helps in prevention and treatment of the disease.7

Although the mean clearance declines with age, the BLSA also demonstrated that the decline in kidney function is variable.8 There was a significant proportion of individuals who maintained kidney function over time. This variability in the decline of kidney function associated with aging is one reason why there can be difficulties in diagnosing early stage 3 CKD (stage 3A), as the Modification of Diet in Renal Disease and other formulas assume an average rate for age-related decline. Research tends to focus on risk factors for kidney function decline and development of CKD. There are few studies that have evaluated the characteristics of older individuals who maintain normal kidney function later in life.

The articles in this issue examine some of the key patient care issues in older adults, as seen by nephrologists. In addition to the epidemiology and measurement issues related to CKD in older adults covered by Dr Stevens and colleagues, Drs. Weinstein and Anderson examine the pathophysiology of the aging kidney, whereas Shlanger and colleagues assess the influence of aging on water and electrolyte metabolism. The dysregulation of sodium homeostasis in older adults contributes to both higher rate of hypertension as well as an increased frequency of symptomatic nocturia. The pathophysiology and evaluation of nocturia have been covered by Dr Boongird and colleagues. As the number of diseases continues to accumulate in kidney disease, the issue of medication dosing and interactions becomes particularly relevant. These have been covered by Drs. Rifkin and Winkelmayer. The presence of kidney disease also complicates medication approach for osteoporosis. Drs Sheru and Fried have addressed the issue regarding the epidemiology and treatment of bone disease in older individuals with CKD.

As hypertension is highly prevalent in the elderly population, leading to both kidney disease and cardiovascular disease, this volume addresses a number of key aspects of hypertension in the elderly population. Drs Kithas and Supiano evaluate treatment options for hypertension in the elderly population. With an increase in age, there are changes in the sensitivity of baroreceptors and an increased risk of orthostasis, which can further complicate the treatment of hypertension. Drs. Fisher and O'Hare review the epidemiology of hypertension in the elderly people with CKD. They highlight the high prevalence but poor attainment of hypertension goals in older individuals. Dr Soni and colleagues describe the extent to which the treatment of hypertension and other comorbid conditions that co-travel with CKD influence physical and mental well-being. Health-related quality of life and patient goals and values should be considered when initiating renal replacement therapy, discussing kidney transplant, or considering end-of-life care in older adults with advanced CKD.

Inability to transfer or ambulate and measures of disability are common in end-stage renal disease.6 The decline in physical function begins earlier in CKD and portends a poor outcome. This has been reviewed by Dr Odden across the spectrum of CKD and has implications for planning for mode of renal replacement therapy. The issues of transplantation candidacy and evaluation and considerations of end-of-life care in the elderly people who often have a high comorbid burden have been covered by Drs. Hartmann and Wu and by Dr Schell and colleagues, respectively.

It is important to note that there are opportunities for both collaborative care and collaborative research. The care of older adults with CKD may be in co-management with geriatricians and may be informed by more geriatric–centric assessments of functional status, social support, and cognitive performance. Because there is a striking gap between the number of geriatricians and the number of older adults, some have argued that the nephrologist should address this need with more training focused on older adults.9 We certainly agree and hope that you do, too.