Kidneys are probably not a subject most of us think about too much – but right now they’re at the centre of a global medical controversy. In a paper published in the British Medical Journal today, we explain how a newly-defined condition called “chronic kidney disease” could turn many people into patients.
The problem is that the boundaries of this “disease” have been set so wide and the threshold defining who is “sick” set so low, that there’s a risk a lot of folk might end up being over-diagnosed. People who are “over-diagnosed” are labelled as having a condition even though it would never harm them.
A wide net
The new framework for the condition called chronic kidney disease was first launched in 2002 by the National Kidney Foundation in the United States. A key motivation was to bring a common language and a sense of order to kidney care – to replace a rather chaotic situation where there were different names for kidney problems, including renal insufficiency and renal impairment.
One of the main aims of the 2002 framework was to try and identify people with the early signs of kidney disease – before it developed into full-blown kidney failure.
A key measurement of the definition is based on a common blood test of kidney function. This measure tends to decline as we get older. And the thresholds used to define those with the disease and those without it, were somewhat arbitrarily decided (as they are with many diseases).
The problem here is that the way the definition was written automatically means that around one in eight adults – and around one in two people over the age of 70 – are defined as having chronic kidney disease.
But being treated for end-stage kidney disease is extremely rare, perhaps happening to only one in every 3,000 people in any given year. As others have noted:
the majority of those held to have CKD have no identifiable kidney disease.
Understandably, there’s a lot of concern among some doctors and others that, for many people, the new definition of chronic kidney disease means the normal ageing of kidneys is being turned into a medical condition.
As we outline in our paper, there’s a vigorous debate underway within the medical community about this new condition, and the risk of over-diagnosis. Our co-author, kidney specialist Richard Glassock, has observed elsewhere that chronic kidney disease is:
like a fishing trawler, it catches many more innocent subjects than it should.
Despite this, an international organisation of kidney disease experts confirmed the 2002 thresholds again in 2012. While some amendments added more complexity to the disease classification system, the fundamentals of the definition didn’t change.
For those of us studying the problem of over-diagnosis, chronic kidney disease appears to be another example of disease labels being given to some people who may not benefit from them.
It’s important to mention that the problem of over-diagnosis can exist alongside the problem of under-diagnosis, where some people miss out on much-needed care.
In fact, the changes in the definition of chronic kidney disease have led to a big increase in specialist referrals, potentially meaning fewer resources, over time, for those with genuine kidney disease.
Our paper on chronic kidney disease is part of a series in the British Medical Journal, looking at the problem of expanding disease definitions and the risk of over-diagnosis.
The series was launched with a paper about the over-diagnosis of a condition called “pulmonary embolism” (blood clots in the artery leading to the lungs).
That research showed that while these clots can be deadly, modern diagnostic technology – CT scans in particular – are finding smaller and smaller clots that are being diagnosed and treated earlier, even though they may never have caused any harm.
The world’s leading medical science journals are increasingly publishing articles on the problem of too much medicine. Recent articles focus on the over-treatment of mild high blood pressure, the lack of effectiveness and potential harms of general health checks, and the over-diagnosis of breast cancer arising from screening.
Just this week, a series of recommendations from the National Cancer Institute called for much great awareness that “overdiagnosis is common”, and argued that some early forms of abnormalities should no longer be called cancer.
Our long-held cultural faith in early detection is being shaken as mounting scientific evidence suggests it can be a double-edged sword.
In our paper, we call for a review of the definition of chronic kidney disease to be conducted by a broad panel of people. We hope this will be part of a wider public debate about how many people we want to define as patients.