Kidney health

Why is kidney health important?

The kidneys are a pair of organs located in the small of the back, one on either side of the spine. They are responsible for filtering and removing waste products from the body (as urine via the bladder), keeping bones healthy and looking after blood pressure. As we age we are at increasing risk of our kidneys working less well, but they may also work less well as a result of certain medical conditions such as diabetes or high blood pressure, or as a result of long term use of certain prescription medicines. It is not always possible to know what has caused a particular person’s kidneys to work less well.

Most people will not notice if their kidneys are working slightly less well than they used to because this does not usually cause symptoms or stop the kidneys from working. In most cases kidney performance is affected in a mild way but remains stable for many years, while for a small minority of people it worsens rapidly and will cause problems with their health. Around one in eight people in the UK have some degree of kidney impairment (i.e. their kidneys are working less well than they used to) - British Kidney patients association, May 2017. For most of these people this will never cause serious problems. In a few people this mild kidney impairment can progress (worsen) so they need treatment for their kidneys. All kidney impairment, whether it be mild or severe, is nowadays referred to by doctors as ‘chronic kidney disease’.

Dr Kathryn Griffith explains who is likely to develop kidney impairment and that for most people kidney function declines very slowly and they will never need dialysis or transplantation.

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We know that as we get older, particularly after the age of 40, kidney function tends to decline anyway, but there are other conditions that can make it decline slightly more quickly. Those are particularly high blood pressure and diabetes but there are obviously some other conditions that run in families, such as Polycystic Kidney Disease, people may take tablets or medicines that can have an effect on their kidneys, and there are inflammatory processes that can affect the kidneys. So there is a great long list of other conditions but for most of the patients that I see in my general practice they will have a declining kidney function which is related to either high blood pressure or diabetes and made slightly more by the fact that they are also getting older.

In most of my patients I would say that most, that they will have it as part of other conditions that they have. Largely because in general practice a lot of the people we have tend to be older, whereas if you work in hospital you will see a different group of patients. And here I work at the university, so some of my people with chronic kidney disease will have it because they’ve got, they were perhaps born with abnormal kidneys, or they’ve had a very destructive inflammatory process which affects their kidney function. They may have got, they may have had recurrent infections because the plumbing system for their kidneys didn’t work very well. So this, here I will see much more a different group of patients and they will have what we call Primary Kidney Disease, something which is just affecting the kidneys, whereas for my older patients it tends to be part of high blood pressure, diabetes, cardio-vascular disease, so they have other processes of affecting other parts of the vascular system.

So one of the issues is that we can actually plot and monitor how kidney function is declining by repeating the blood test on a regular basis, perhaps once or twice a year. And we can see that for most people kidney function will only decline at about 1 or 2% per year. And they will never reach the level at which they may need dialysis or transplantation. And we are talking there about levels less than 15%.

The term ‘chronic kidney disease’ (often shortened to ‘CKD’) is problematic for several reasons. Many people interpret the term ‘chronic’ to mean severe, although in medical language it means that the condition is a long term one rather than something that has a rapid onset and progression that may be quickly put right (known as an ‘acute’ condition). This misunderstanding can lead to unnecessary anxiety among patients who may think their kidney performance is worse than it is.

Dr Kathryn Griffith explains that the term ‘chronic’ in chronic kidney disease means that a decline in kidney function has been detected over a period of at least three months.

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So you may have been told that you or your family member have got chronic kidney disease, and that’s quite a complicated term to take on board. It’s important to know that when doctors and nurses talk about ‘chronic’ they mean a condition that’s been going on over a period of time. And with chronic kidney disease we are talking about a change in the kidney function for at least 3 months in time. Disease is an interesting concept that people worry about as well. Unlike one process that can affect the kidneys, for chronic kidney disease there are actually several of them that can cause the kidneys to work less well.

In addition, some professionals argue that impaired kidney performance is not a disease as such. Rather, it is an indicator that a person may be at increased risk of developing other health problems, in the same way that having a high cholesterol level is not in itself a disease, but it increases the risk of cardiovascular disease.

Dr Dan Lasserson explains that kidney impairment is not necessarily a disease but it raises risks and therefore needs a label, and that that label should be used consistently.

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When I approach this as a researcher as well, as well as a clinician, it’s pretty clear to me from what we call epidemiology - which is looking at what happens to populations of patients who have the same kind of condition in terms of, say, the risk of developing heart failure or having a cardiovascular event, such as a heart attack or a stroke - it’s pretty clear that, when someone does have chronic kidney disease, those risks are raised and it’s important, therefore, that we in the medical profession are able to communicate and talk about that risk and advise patients on the various options that are available to reduce risk, so people can decide what it is that suits them best as how they can keep themselves as healthy and living as long a life as possible.

So we are often caught from the research and the practice side from sort of two ways of looking at it, if you like. So somebody with chronic kidney disease at an early stage, for example, say, stage 3A, they will, you know, walk into a GP’s surgery, they may have hypertension, may have diabetes or may have none of those two but perhaps would be slightly older, and they’ll look quite healthy. And I think in order for some doctors to call that a disease state they find quite challenging.

When I look at it from the perspective of risk and what it is that I need to be telling my patients about things, conditions that they may have that raise risks and what to do about it, then I think it’s important that those labels are used because they have meaning.

So, although I’m aware that there are doctors that do not use this label, I look at it from a slightly different angle and say, well, don’t just look at the patient in terms of how they appear today, you need to think about risk long term. And also it’s important that diseases are diagnosed in a pretty systematic way, so the same for each patient each time they will see a doctor or a different doctor. And it may be that we need more research evidence might convince some doctors who don’t want to call this a disease.

And I think what we don’t want is for this to kind of dissolve into what one might call a semantic argument, an argument about meaning. Is it about the risk of a disease or a disease in itself? And you can say that’s a bit similar to like high blood pressure - hypertension - because that causes, you know, there is a risk of things like heart attack, stroke, heart failure, and declining kidney function, happen because of high blood pressure. And doctors are very happy to diagnose that and manage it where appropriate. And you can see sort of chronic kidney disease in sort of the same way. It doesn’t necessarily make you unwell in the early stages, so the patient with hypertension or with early stage chronic kidney disease will look quite fit and healthy, potentially, but in the hypertension case - patients with high blood pressure - doctors will very happily make a diagnosis and offer treatment and lifestyle advice and talk about how, what kind of treatment regimen would be easier for a patient to adhere to or what kind of treatment goals the patient may want to achieve. And we could say the same for chronic kidney disease. It’s not necessarily a disease state like a heart attack or a stroke, but it raises risks and, therefore, giving it a label that makes people recognise it, apply it systematically and then act in terms of advice and informing patients what their risks are, is really important.

So, whilst I know there are some doctors that don’t like using the term, for me it’s pretty clear and unambiguous that we should be using this term. We should be applying it systematically so patients get the same view and the same understanding of their illness at every healthcare contact, where they may want to raise it and talk about it as an important issue for them. And also it’s important I think that we fully inform patients of their risk so that they’re able to take whatever action from a range of possibilities that there are from the clinical perspective.

Dr Dan Lasserson explains that having chronic kidney disease increases the risks of cardiovascular disease in its own right and not just because of other conditions people may have alongside it.

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So chronic kidney disease is an extremely important risk factor for cardiovascular disease, such as heart attack or stroke. And we know that patients, some patients with chronic kidney disease also have other problems, such as high blood pressure and diabetes, both of which will also increase the risks of cardiovascular disease. However, in the studies that have looked at large populations of patients with chronic kidney disease, and with high blood pressure, and with diabetes, among other things such as high cholesterol, which can also increase vascular disease, it’s clear that it’s not just the fact that patients with chronic kidney disease have other things that are making them at increased risk, there’s something about chronic kidney disease itself that raises risk. It’s not just due to the other comorbidities or conditions that a patient may have. And we don’t yet know fully why that’s the case. There are a number of very good studies that pinpoint certain hormones of the kidneys involved with regulating, particularly to do with blood pressure and salt and water. But we don’t yet fully know why chronic kidney disease increases risk.

As kidney function declines, blood pressure becomes more difficult to control. Blood pressure variability may play a part in that. We know that patients with very advanced chronic kidney disease have very variable blood pressures. We also know from other evidence that patients without chronic kidney disease who have variable blood pressure are at more risk of stroke and heart attack than, say, patients whose blood pressure doesn’t vary quite so much. That’s all quite early research findings. We haven’t, we don’t yet know how we can use that in clinical practice but we are, and a number of people are undertaking studies that will look into that. So I think the short answer is, although we know that chronic kidney disease does raise risk and does it in its, on its own merits, if you like, we don’t yet fully know what that mechanism is, and when we do, we’ll be able to think about alternative therapies that might be, might help us to target specifically the cardiovascular disease risk of chronic kidney disease.

Research evidence shows that, as well as being at increased risk of cardiovascular disease, people with chronic kidney disease are also at increased risk of experiencing something known as acute kidney injury - often shortened to AKI. This is a major cause of avoidable harm and an often unrecognised but underlying cause of death in hospitals. Doctors knowing which of their patients are at risk of AKI, and being able to tell this to patients in advance, is important for prompt recognition and treatment.

Dr Dan Lasserson explains what acute kidney injury is and how it differs from chronic kidney disease.

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So AKI is acute kidney injury and this is a really important condition. It’s important for healthcare to recognise it happens in the community and also in hospitals too. And in both settings it’s really important that we rapidly recognise that it’s going on and take steps to treat it. What is it? Well, it’s a sudden reduction in the body’s ability to filter the blood and produce urine. And typically this would be detected by a blood test, where we would see a rise in the patient’s creatinine. And that’s, creatinine is a waste product that the kidney gets rid of for us, and so when it rises in the blood it shows the kidney isn’t getting rid of it as well as it should be. And that’s our sign to think about AKI as being a cause of this and what we might do about it.

In our frailer and older patients they may have a sudden change in their function, reduced mobility or just not being quite right, and in that setting, often that’s a cause of AKI as well. In very mild stages patients may not notice anything but we would know that typical causes might be dehydration. Some medications can do it as well, if there have been changes in medications recently. Infections as well. And also AKI can happen at the same time as other significant conditions where maybe the kidney hasn’t been the primary focus of a condition or disease, if you like, but it’s being affected because another serious disease is happening, like overwhelming or generalised infection, or chest infection, for example.

So what’s the difference between CKD and AKI?

So the difference between AKI and CKD, if you like, is that chronic kidney disease represents a stable state over a longer period of time, where day in day out the kidneys are functioning but functioning less well than we would like, and that’s pretty stable day in day out. AKI is when there’s a sudden reduction in kidney function; and, usually, that’s associated with symptoms or with a change in function. In early stages of AKI it can be, the patient may not notice anything until it gets to a more advanced stage. But, by and large AKI is associated with acute illness, often perhaps due to dehydration or to a change in medication, or the kidney is being affected by another disease process such as pneumonia, potentially heart failure as well.

Dr Kathryn Griffith talks about the circumstances in which acute kidney injury might arise and how it could be prevented from happening.

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Are there any specific circumstances in which acute kidney injury might arise?

In my patients, the patients I get concerned about who have a moderate decline in their kidney function but they are taking lots of tablets or medicines, and particularly groups of tablets or medicines that can have, can make the kidneys slightly more vulnerable are those people taking drugs for heart failure and for high blood pressure. And these are drugs which fall in the category of either, we call them ACE inhibitors, and they often end in ‘pril’, So you might have heard of drugs like ‘ramipril’, ‘perindopril’ and the other cousins of those drugs are something we call ‘angiotensin receptor blockers’, and they tend to end in ‘sartan’, so drugs like ‘candesartan’, ‘losartan’. Now these, both families of drugs are actually life-saving drugs when they are used in the right circumstances they can help protect the kidneys. But the issue is if you have an illness such as diarrhoea and vomiting and that means that you are dehydrated and you drop your blood pressure. If you are taking these drugs which otherwise are very clever at lowering blood pressure, you can’t actually raise your blood pressure to help protect your kidneys. The kidneys really like to be, operate, at the right pressure. They like to have not too much, which can damage them, and not too little, which means they can’t filter. And if they can’t filter then you get a build-up of waste products in the blood stream and we pick that up on blood tests as acute kidney injury. So all patients who are taking combinations of either those ‘A’ drugs, which are the ACE inhibitors, or the angiotensin receptor blockers, particularly when you are also taking water tablets, which we call diuretics, those are things like ‘furosemide’ or ‘bumetanide’. There are other different water tablets such as ‘spironolactone’ or ‘eplerenone’. Again these are tablets which are used to clear fluid and they will tend to lower blood pressure, which is great when there’s too much fluid on board, but if you’ve got sickness or diarrhoea and you haven’t got enough fluid in the system and the body wants to hold on to it, they can have an adverse effect on kidney function. So remember that tablets work. They have, they’re important in the right circumstances but there are some circumstances where they may not be beneficial and that you should be aware of this. And often patients will have a card and be recommended to stop them or at least phone up, phone up either in-hours your own doctor, or your heart failure nurse if you have one or, or phone up the out-of-hours number and get some advice and ask about these tablets should you have sickness and diarrhoea.

So if somebody is unfortunate enough to have an episode of acute kidney injury is it something they can recover from?

Well we always used to think that people recovered completely. We now know that some people don’t, and that’s an issue. So you can start off with your kidney function being 50%. You can have an episode when your kidneys aren’t working very well with acute kidney injury it could drop perhaps down to 30%. It may recover partially. Perhaps to 40%. But often it doesn’t completely get back up to where you were. Now again, that may not have a long term effect it really start, depends on where you start. but these episodes could perhaps have been prevented or reduced by having the right advice and the right treatment.

There’s a big emphasis now in hospital, because we know that acute kidney injury isn’t uncommon, it’s not uncommon on the surgical wards if someone has a problem with bleeding, a lot of bleeding. It’s certainly not uncommon on the elderly wards perhaps after a stroke where people aren’t able to drink properly. So there are circumstances that it, that we recognise that it can occur, and there are big campaigns now and nationally about raising awareness of acute kidney injury and helping to protect people’s kidneys.

Dr Dan Lasserson explains why chronic kidney disease makes people more prone to acute kidney injury.

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Why does early stage CKD make you more prone to AKI? Well, a lot of patients with early stage CKD are older. Many of them may have conditions such as hypertension and diabetes, and a number of medications will be, could be prescribed for those which affect the kidney, for example, ACE inhibitors or angiotensin receptor blockers. These drugs are a really important part of our ability to reduce risk long term in patients with hypertension and some with diabetes too. So they’re important drugs that are beneficial for patients if they’re handled in the right way. Whereas after, say, a period of diarrhoea or vomiting or dehydration, sometimes those drugs can start harming the kidney, and the earlier we can recognise that’s happening and stop those medications while the patient’s kidney function recovers, the better; and then they can go back on those medications safely at a later date.

So some of the risk around AKI for patients who have early stage CKD is around some of the medications they’re taking. It may be an indicator of also age and frailty as well. We know that our older and frail patients are more susceptible to dehydration in hot weather and are at greater risk of their kidney being involved in a condition like pneumonia or heart failure, for example.

So that explains some of it. There are also probably some other mechanism around how the kidney functions that is affected in CKD that we haven’t fully worked out the mechanism yet, how it goes from A to B. But understanding that CKD is a prominent risk factor for AKI is important for all doctors and for all patients who are affected as well, so that communication can be delivered ahead of time, and how to, how patients respond on days when they’re unwell and they’re losing fluid and salt through diarrhoea or vomiting, or because it’s just been very hot and they haven’t been able to keep up with their fluids.

The term ‘chronic kidney disease’ is used to cover all levels of kidney impairment, ranging from a tiny decline in kidney performance that causes no symptoms and may have no effect on someone’s long term health, to a life-threatening condition that requires regular dialysis or a kidney transplant and has a significant impact on daily life. Chronic kidney disease is therefore divided into several stages based on the level of decline in performance. Stage 1 represents the smallest decline in function and stage 5 the worst. Symptoms don’t usually occur until the decline reaches stage 4; treatment with dialysis and/or a kidney transplant will be offered at stage 5.

Although scientific evidence shows that people with kidney impairment are at increased risk of many adverse outcomes, some doctors are reluctant to label people with early kidney impairment as having a disease. Here two experts speculate on some of the possible reasons for this reluctance.

Professor Gene Feder explains that if a GP is already treating a person’s cardiovascular system then that will also protect the kidneys.

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Now people who have heart disease, or coronary heart disease as it's called, have blockages in the arteries in the heart and they also have a higher risk of having blockages in the arteries going to the brain and to the kidney. So it's part of a more general – what’s called vascular condition, and there are specific treatments that can help prevent further damage. But if you don’t know that the kidneys are involved that treatment may not be as specific.

Now the truth is that really good treatment to prevent another heart attack, or indeed to prevent the first heart attack if you're at high so-called cardiovascular risk is fundamentally, would also, will protect your kidneys and that means specifically keeping your blood pressure at a relatively low level, which sometimes requires drug treatment. So you could argue that if a GP is looking after their patient with diabetes and raised- or raised blood pressure or high cardiovascular risk properly for those problems, there isn’t much additional that they can really do in relation to the kidneys. Which is one of the reasons why GPs, up till now, have not necessarily emphasised that there may be a reduction of kidney function to their patients because if they're already doing all the right things - the patient doing all the right things and the GP doing all the right things to prevent further complications, say, from high blood pressure or diabetes - then that is also going to protect the kidneys.

Dr Dan Lasserson says that test results that were once considered as within the normal range are now reported as abnormal because of new research evidence about risk.

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Some of this may be to do with the blood tests. So these are blood tests that GPs have been doing for years and years and years on their patients and they haven’t been told that the numbers they’re getting back from the lab are abnormal. And the same patient given the same blood test now comes back with a note from the lab saying, actually, this is abnormal, when for years it hasn’t, for years it’s been in what’s called the normal range. And I think what’s happened is research has very much changed that perspective. For those individual doctors, they haven’t seen those patients getting more unwell with a different label, it’s just come from the laboratory. And that might explain why some doctors are reluctant because they don’t see there being any particular change in this group of patients but the laboratory advice is coming back different. However, it’s clear, from recent research, that there is an excellent reason to change how the laboratory reports these blood test values because they actually do show there’s a higher risk. And, for some doctors who’ve maybe been practising for years and seeing these results as being normal, it’s quite a paradigm shift for them to then suddenly say this is a disease.

Please read the next topic summary to learn how and why kidney function is monitored by doctors and what people can do to help look after their kidneys.

Last reviewed August 2017.
Last updated August 2017.