Chronic renal failure (CRF) is a term used when the kidneys are not working as well as they should. The term implies that both kidneys are affected. This is because one normal kidney is enough to maintain normal kidney function throughout life.
How does the urinary system work?
The urinary system consists of the kidneys, ureters, the bladder and urethra. The kidneys filter the blood to remove waste products and produce urine. The urine flows from the kidneys down through the ureters to the bladder, where it is stored until we go to the toilet. It passes through another tube called the urethra to the outside when urinating (peeing).
The kidneys contain millions of tiny filtering units called glomeruli. As blood passes through the tubes in the glomerulus, waste products pass through the walls of the tubes to form urine. Blood cells and other things such as protein cannot pass through the walls because they are too big.
What causes CRF?
When both kidneys are damaged, they cannot keep up with the work that is asked of them, so that they may slowly fail over the years. When their function becomes very poor, terms other than CRF are used, like ‘end-stage renal failure’ (ESRF). This term is not a very good one as it implies that there is nothing more that can be done, but in fact it means that there is a need for dialysis or transplantation to maintain good health. Dialysis and transplantation are often called ‘renal replacement therapy’ (RRT).
The causes in children are very different to adults, as most children with CRF have been born with abnormal kidneys. Less commonly, an illness causes damage to the kidneys during childhood. Occasionally, there are illnesses that run in families or have a genetic cause.
How can we measure how well the kidneys are working?
We can measure kidney function, or how well they are working, by measuring the level of creatinine in the blood. This is a very good marker of kidney function.
This is because it is produced in the body at a constant rate everyday during muscle movement, and only the kidneys remove it in urine, although it is not poisonous in any way. Therefore, if the kidneys work less well, the creatinine sets at a higher level in the blood.
Because it comes from muscle, the level in the blood depends on a person’s size and therefore the amount of muscle someone has, so the level in a man would be higher than in a woman, which would be higher than in a child, which would be higher than in a baby.
We would expect the creatinine levels to increase through childhood until adult size is reached. However, if the creatinine level is consistently above the normal range for age, this means that the kidneys are not working normally and the person has CRF.
Glomerular filtration rate (GFR)
The creatinine does not increase above the normal range until the kidneys are working at about half of the level that they should, so sometimes we need a more accurate way to measure kidney function. We may also need this if we are not sure how quickly, or if at all, the kidney function is getting worse.
We can measure this using a glomerular filtration rate (GFR) test. This involves injecting a substance that is only taken out of the blood by the kidneys. By watching how quickly it goes from the blood by taking a series of blood samples and measuring the amount of the substance left, we can calculate how well the kidneys are working. This result is called the GFR.
The GFR result is measured in millilitres per minute per 1.73m² (ml/min/1.73m²). The normal range is 80 to 120 ml/min/1.73m². Levels of 60 to 80 are usually considered to be mild CRF, from 30 to 60 is moderate CRF and from 15 to 30 severe CRF. When the GFR result falls below 15, dialysis or transplantation is usually needed.
Does CRF get worse?
Usually when both kidneys are affected and the GFR is below normal, the kidney function gets progressively worse. However, this does not always happen and in some children, kidney function can stay stable for many years, or even improve, especially in the first year of life. The decline in function seems to happen because the kidneys cannot cope with the extra work put on them and they ‘tire out’ more quickly than they should.
Deterioration of kidney function is usually very slow, so that we pick it up on blood tests before you notice any changes in the child. Abnormal kidneys may not be able to grow as the child grows, and so cannot keep up with the work they need to do. As they cannot grow properly, they become progressively smaller relative to the size of the child. This may particularly be the case during puberty, when the child is growing very fast, so this may be a time when kidney function gets worse more rapidly.
Another reason in some children is that it is not possible to stop the disease that is causing the kidney damage. Finally, if the blood pressure goes up or if protein appears in the urine, these too can make kidney function get worse. A rapid decline in kidney function may happen if the child becomes unwell for another reason, such as an episode of diarrhoea and vomiting or during a urinary tract infection, although when these are the cause, the kidney function usually improves again.
What can we do to slow down the progression of CRF?
The most important thing is to attend clinic regularly and follow the instructions carefully on any medicines that may be required. The child’s nutrition is an important part of his or her treatment so it is important to follow any advice from the dietitian.
As we do not really know how quickly kidneys get worse in children with different diseases, it has been quite difficult to assess whether any treatments help to slow the progression of CRF. In adults, it has been shown that if there is protein in the urine (proteinuria) this is bad for the kidneys and CRF progresses more rapidly than if there were no proteinuria.
Giving a medicine that reduces the pressure in the little filtering units (called glomeruli) in the kidneys can reduce protein in the urine. These medicines are called ACE inhibitors. We do not know if they have any benefit in children or even if proteinuria is associated with a more rapid decline in GFR in children. However, in some children, we do use these medicines and we will discuss this with you in more details if we decide to use them.
Raised blood pressure can make the kidney function worse, so we check your child’s blood pressure each time you come to clinic.
In some children with structural abnormalities in the urinary tract, urine infections (UTI) can damage the kidneys so we need to make sure that all is done to prevent UTIs. Also, the drainage system may not be good enough and our urologists will address this if it is a possibility.
Does the CRF progress at a constant rate?
This depends on the cause of the CRF and can be very variable in childhood, varying from very stable function to a very rapid decline. Sometimes, there can be a speeding up of deterioration, as the CRF gets worse. If we are concerned about this we may need to see the child more often. It would be very unlikely that we would be ‘caught unaware’ because we will be monitoring blood results as often as necessary.
What are the effects of CRF?
The effects depend on how severely the CRF affects the child. Most children have very little in the way of symptoms until their GFR is less than 40 and many cope very well when it is below this level.
Symptoms can include tiredness, nausea and loss of appetite. Headaches can occur if the blood pressure becomes a problem but this is uncommon in children until CRF is severe. Many children born with abnormal kidneys are unable to concentrate their urine so pass very large volumes. They therefore need to drink a lot to compensate, particularly if they are losing fluid with diarrhoea, vomiting or fever.
What checks do we do at clinic?
Growth and progression through puberty and dietary assessment
CRF can affect growth. The main cause for this is poor nutrition, which may be due to reduced appetite or vomiting. We will check the child’s growth carefully and our dietitian may help with advice to improve his or her nutrition.
It is very important that we do not allow growth to become abnormally slow as this may affect your child’s final height.
Progression through puberty may also be affected, so we may need to examine him or her. Very rarely, if growth is poor despite the best nutrition, we may prescribe growth hormone. Vitamins may or may not be necessary as some can reach too high levels in CRF and some may need to be given. Our dietitians will advise on this.
The child’s nutrition is very important for growth and well being. Our dietitian will individually assess your child and will give practical suggestions to help maximise his or her intake. If your child’s appetite is poor, there are various palatable supplements to try.
However, many children, and in particular the younger ones, need to be tube fed to supplement the nutrition intake from their diet. Most children who need extra feeds long term will have a tube placed directly into the stomach (gastrostomy) by the Surgical team.
Parents often look for information about diet in renal disease in books and on the Internet. However, we recommend that you do not do this. Information is usually aimed at the treatment of adults with CRF, whose renal problems may be quite different to those found in children. The advice is not appropriate for children and may potentially be harmful.
Children’s needs are different. They need adequate nutrition to grow whereas adults have done all of their growing. Vitamin tablets and cod liver oil may not be appropriate and should not be given with being discussed with your dietitian or doctor. Parents should ask their doctor to refer them to a dietitian if they are concerned about their child’s intake – please don’t alter a child’s diet without speaking to us.
Blood pressure can be low in some children with CRF as their kidneys ‘leak’ salt and water. These children usually need to drink a lot and should always carry a drink with them. They also usually like salty food and may need to take salt supplements.
On the other hand, some children cannot get rid of salt and water as easily as they should, so need to reduce their salt intake. These are the children who develop problems with high blood pressure.
To make things more complicated, some children who start as ‘salt losers’ or who can deal with salt normally develop problems as their kidney function declines. We will advise parents about the salt intake that their child needs and the dietitian will advise how to reduce salt intake if necessary.
We test the child’s urine with dipsticks for protein. We then send the sample to the laboratory to measure the amount of protein it contains more accurately. If the protein is increasing, it may mean that the rate of decline in kidney function is increasing and we may consider prescribing ACE inhibitors.
Creatinine level and evidence for deterioration of kidney function
We check the child’s creatinine level at every visit and plot the results on a graph so we can see how the level is changing. If the level has gone up more than we would expect, we may call you back to clinic sooner than planned, as this means that your child’s kidney function has got worse. However, there can be reversible causes for worsening kidney function, which we will investigate.
Blood acidity (bicarbonate)
The kidneys are responsible for regulating the acidity of the blood, which needs to be kept within particular limits for the body to work at its best. In some children, their blood may become acid, and they need to take an alkali (sodium bicarbonate) to counteract the acidity.
Urea is produced when protein in the diet is broken down to be used for growth. The urea level in the blood depends on the protein and calorie intake in the diet. The urea level can also go up if the protein intake is very high or the calorie intake is very low as this reflects the breakdown of protein from muscle as a source of energy. If the urea level goes too high, it can make the child feel very ill and can make other body processes work less well. Our dietitian will give advice to control the urea level if necessary.
Calcium, phosphate and parathyroid hormone (PTH)
The kidneys are responsible for getting rid of the phosphate that we eat. Phosphate is present in protein-containing foods and especially dairy products. In CRF, the level of phosphate in the blood can be too high. This is bad as it causes increased production of a hormone called parathyroid hormone (PTH).
This hormone causes damage to the bones, the bone marrow that makes the blood and also to the lining of the blood vessels. Phosphate itself is bad for the blood vessels. We therefore control the amount of phosphate in the diet and if necessary, give calcium carbonate with food to bind the dietary phosphate in the gut and stop it being absorbed.
High PTH levels can also be caused by a lack of the active form of vitamin D. The vitamin D that we eat in our food and make in our skin when we are in sunlight has to be activated by the kidney before it can work. Therefore in CRF, many children need to be given the active form of vitamin D as they cannot make this activation step.
Anaemia (haemoglobin and iron levels)
The kidneys make the hormone called erythropoietin that is necessary to make red blood cells. Children with CRF can therefore become anaemic. If the child becomes anaemic, the level of haemoglobin in the blood falls. Erythropoietin has to be given by injection under the skin just once a week. Iron needs to be given as well to help make the blood.
Folic acid is needed to make red blood cells, but it is also prescribed because it seems to have a protective effect against heart and blood vessel problems, which are a particular problem for children with CRF.
Is my child’s bladder going to need any tests or surgery?
Some children, usually boys with posterior urethral valves, may have small bladders that work under high pressure or do not empty properly. If the child has an abnormality that affects the bladder we may need to do special studies (urodynamics) to look at this.
This is because we must be sure that the bladder will not affect the outcome of the transplant. Some children may need bladder enlargement to both increase the amount of urine it can hold and also to reduce the pressure in it so that it does not damage the transplant.
In some cases it may be necessary to create an artificial channel that connects the bladder to the wall of the tummy to drain the bladder.
This is called a Mitrofanoff. This channel does not let urine out without a catheter being passed down it to drain the bladder. The urology team will discuss any tests or surgery needed in detail with you.
What do we need to do when we are reaching the need for dialysis or transplantation?
Dialysis and transplantation are often called ‘renal replacement therapy’ (RRT). When we think there is a need for RRT within the coming year, we begin to make plans. Ideally, we would like to transplant before dialysis is necessary, which is called pre-emptive transplantation.
This is for four reasons:
- We believe that a successful transplant is the best treatment for children with ESRF, making their lives as normal as possible.
- We want to preserve access points for dialysis (arm and leg veins for haemodialysis and the peritoneum for peritoneal dialysis) for the future, as children with ESRF are likely to alternative between dialysis and transplant in their future lives.
- The long-term mortality is lower with a transplant than with dialysis.
- The risks of deposition of calcium in the blood vessels with long term blood vessel damage is high on dialysis.
However, this plan may not be possible in conditions that require both kidneys to be removed and a period of dialysis, such as focal segmental glomerulosclerosis (FSGS).
Preparing for transplantation
There are many steps to preparing for transplantation and a rough outline of the steps follows:
- We will discuss with parents the pros and cons of parental donation and cadaveric donation. If parents wish to consider donating, we will check their blood group to ensure that this is a possibility. If this is satisfactory, we will arrange more blood tests (tissue typing) for parents and their child and will refer them to our transplant surgeon for a full discussion.
- We will discuss dialysis options in case this becomes necessary.
- All the child’s vaccines, including BCG and hepatitis B, must be up to date. We will check the child’s immunity and prescribe a top up of any vaccines that have not ‘taken’. We will also vaccinate against chicken pox if the child is not immune. Glandular fever (EBV) vaccine may be available soon.
- We will check that there is not a tendency for blood clotting, which might cause the transplant to clot off, but this only involves a blood test.
- We may need to check that the main blood vessels that the transplant surgeon will need to connect the new kidney are all normal. This is not needed in all children. All children will have an ultrasound, but some may need another scan called an MRI scan.
- We will check that we have an up to date bladder assessment from the urology and urodynamics team in children with structural abnormalities of the urinary system and look at bladder emptying by ultrasound in others.
- All families meet with our psychosocial team so you can discuss any non-medical issues and support can be offered as necessary.
- Parents will meet with our team of clinical nurse specialists, who are very important in the care of children on dialysis and after a transplant. They will explain the practicalities of the way forward in more detail.
All of this takes time and that is why we need to plan ahead.
Is there a risk that my other children have this or that they might pass it on to their own children?
Some causes of CRF do run in families. Some can be screened for using ultrasound. Others need more sophisticated tests. We will refer parents to our genetics department if this is a possibility.
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