Long Live the Older Kidney

Shabbir M.H. Alibhai
Senior Editor
Geriatrics & Aging

We have, by some measures, come a long way in our ability to diagnose and treat renal disease. From molecular biology to organ transplantation, medicine has revolutionized the therapies that are available for patients with this condition. In this issue of Geriatrics & Aging, you will find articles that highlight some of the ways in which we have advanced in our understanding of the diagnosis, management, and progression of renal diseases in the elderly.

Whenever I think about renal disease and older people, I think about the topic of denying dialysis to senior citizens. Not so long ago, some industrialized nations had barriers erected to prevent chronic dialysis for people who had reached a certain age. This was done on the pretense that (a) dialysis is a scarce resource; (b) scarce resources need to be rationed; and (c) that younger people will derive more benefit from dialysis than will older people who have limited life expectancies.

Few people today would disagree with the first and second premises. However, support for the third premise is tenuous because the implication is that age is the major determinant of worthiness, productivity, or some similar construct. Younger people are more productive, so the theory goes, and so they should receive dialysis to prolong their lives and allow them to continue to contribute to society.

Many factors besides chronological age go into the equation to determine who is worthy to receive a scarce resource.

A person's worth is difficult to measure, even if we agree that it is morally permissible to allocate resources based on worth. While I do not want to turn this editorial into a diatribe on the ethics of resource allocation, gerontologists see worth in more than economic terms. People can contribute to society through their previous work within or outside the home, their nurturing and support of the multi-generational family, their teachings, their volunteerism, their collective wisdom and experience, their political advocacy, and perhaps even their very presence. Many factors besides chronological age go into the equation to determine who is worthy to receive a scarce resource. Perhaps this is better stated from a practical perspective. If a patient with newly diagnosed, end-stage, renal disease required dialysis, a nephrologist would, for example, look beyond whether he was 55 or 75 when deciding whether to offer him or her the option of dialysis.

There is obviously much more to the treatment of renal disease in the elderly than dialysis. However, have we, as a profession, really grasped the fundamentals of renal disease and aging? Have we integrated this knowledge into our day-to-day clinical lives? I fear not. By way of example, consider the lowly serum creatinine, a simple, cheap measure of renal function. Clearly, it is an indirect measure of glomerular filtration rate (GFR), but a measure nonetheless. In turn, GFR is a fundamental measure of renal function. As GFR declines, many drugs require dose adjustment or are relatively contraindicated. Common examples include NSAIDs, numerous antibiotics, H2-blockers, metformin, digoxin, ACE inhibitors, allopurinol, and others.

We have been taught in medical school that GFR declines with age, at a rate of about 7-10 mL/min per decade of life after age 30. While this is generally true, not every older person's GFR declines at a predictable rate. Serum creatinine is a poor measure of GFR in many older people, especially those who are frailer. Despite having at least nine published formulae to calculate GFR from simple variables (including serum creatinine), none of them perform impressively well. The Cockcroft-Gault formula, a gift from Canada to the world (one of the two authors was Canadian), is very commonly used to estimate GFR. Yet it underestimates GFR in up to 30 per cent of seniors, and sometimes underestimates GFR by a third or more. Thus, despite our increasing knowledge of nephrologic illnesses, we still do not have a simple and precise method to estimate GFR in an older person.

At the end of the day, many physicians do think about GFR when prescribing drugs to their older patients, which is a good start. We think about serum creatinine, and occasionally calculate GFR using the Cockcroft-Gault, or a similar equation. This is even better. Rarely, we will even do timed urine collections to directly measure GFR. Once we have an estimate of the GFR, I hope we use this information to wisely prescribe medications, or alternatively, to refrain from prescribing--the wiser of the two choices is sometimes unclear. Unfortunately, we are not always as wise when it comes to referring our patients with a diminished GFR for nephrologic consultation; or else we wait until there is little to do other than make preparations for dialysis or death.

I suspect that we might do more for the health of our seniors by finding a method that accurately measures GFR, and by figuring out what to do if this measure is abnormal, than we will by perfecting techniques for renal transplantation. Yet it will come as a surprise to no one that we spend far more studying the latter than the former. We still have a long road to travel.