Wednesday, December 21, 2016

Do Not 'Kid' Your Kidneys

Kidney Function Blood Test

Routine kidney function is one of the most commonly performed blood tests.

The kidneys

The kidneys regulate the amount of water and salts that we have in our bodies. They do this by filtering the blood through millions of structures called nephrons. The kidneys also pass out certain waste products from the body. Urine is made up of the excess water, salts and waste products passed out by the kidneys down to the bladder.

Routine blood test of kidney function.
The usual blood test which checks that the kidneys are working properly measures the level of urea, creatinine and certain dissolved salts.

Urea is a waste product formed from the breakdown of proteins. Urea is usually passed out in the urine. A high blood level of urea ('uraemia') indicates that the kidneys may not be working properly, or that you have a low body water content (are dehydrated).

Creatinine is a waste product made by the muscles. Creatinine passes into the bloodstream, and is usually passed out in urine. A high blood level of creatinine indicates that the kidneys may not be working properly. Creatinine is usually a more accurate marker of kidney function than urea. The effect of muscle mass needs to be taken into account. A person with a lot of muscle and little fat on their body is likely to have a higher creatinine than a person who has a lot of fat and little muscle.

Estimated glomerular filtration rate (eGFR) provides a guide to kidney function. Although the level of creatinine in the blood is a useful guide to kidney function, the eGFR is a more accurate measure. Blood creatinine can be used to estimate the eGFR using age, sex and race. This is often calculated by computer and reported with the creatinine blood test. The normal value for eGFR is 90-120 ml/min. An eGFR below 60 ml/min suggests that some kidney damage has occurred. The value becomes lower with increasing severity of kidney damage.

Dissolved salts that are routinely measured are sodium, potassium, chloride and bicarbonate. They are sometimes referred to as 'electrolytes'. Abnormal blood levels of any of these may be due to a kidney problem. (Some other conditions may also alter the salt balance in the blood.)

[[Estimated Glomerular Filtration Rate
Various different diseases, conditions and medicines can affect the function of the kidneys. The estimated glomerular filtration rate (eGFR) does not diagnose any kidney disease but is a test to
assess how well your kidneys are working. A reading of greater than 90 ml/min/1.73m2 is normal.

What is the estimated glomerular filtration rate (eGFR)?

The eGFR is a test that is used to assess how well your kidneys are working. The test estimates the volume of
blood that is filtered by your kidneys over a given period of time. The test is called the estimated glomerular
filtration rate because the glomeruli are the tiny filters in the kidneys. If these filters do not do their job properly
then the kidney is said to have reduced or impaired kidney function.

The eGFR test involves a blood test which measures a chemical called creatinine. Creatinine is a breakdown
product of muscle. Creatinine is normally cleared from the blood by the kidneys. If your kidneys are not working
properly, the level of creatinine in the blood goes up.

The eGFR is then calculated from your age, sex and blood creatinine level. An adjustment to the calculation is
needed for people with African-Caribbean origin.

Stages of kidney function

The level of kidney function is divided into five stages:
Stage of Chronic Kidney Disease (eGFR;ml/min/1.73m)

Stage 1: the eGFR shows normal kidney function but you are already known to have some kidney damage or disease. For example, you may have some protein or blood in your urine, an abnormality of your kidney, kidney inflammation, etc.
(90 or more)

Stage 2: mildly reduced kidney function AND you are already known to have some kidney damage or disease. People with an eGFR of 60-89 without any known kidney damage or disease are not considered to have chronic kidney disease (CKD).(60 to 89)

Stage 3: moderately reduced kidney function. (With or without a known kidney disease. For example, an elderly person with ageing kidneys may have reduced kidney function without a specific known kidney disease.) (45 to 59)-(3A); (30 to 44)-(3B)

Stage 4: severely reduced kidney function. (With or without known kidney disease.)  (15 to 29)

Stage 5: very severely reduced kidney function. This is sometimes called end-stage kidney failure or established renal failure.
(Less than 15)

Note: it is not possible to assess the estimated glomerular filtration rate (eGFR) accurately in people with abnormal amounts of muscle and in people who have conditions that can affect the level of creatinine. This includes:

>People with muscle wasting conditions.

>People who have had an amputation of an arm or leg.

>Malnourished people.


>People with acute kidney failure.

>People with a lot of fluid retention (edema).


Who has a blood test of kidney function?

 Routine kidney function is one of the most commonly performed blood tests. It may be done:

>As part of a general health assessment.

>If you have suspected low body water content (dehydration), when the urea level increases.

>If you have suspected kidney failure.(Read below, Acute Kidney Injury)  The higher the blood levels of urea and creatinine, the less well the kidneys are working. The level of creatinine is usually used as a marker as to the severity of kidney failure. Creatinine in itself is not harmful but a high level indicates that the kidneys are not working properly. So, many other waste products will not be cleared out of the bloodstream. You normally need treatment with dialysis if the level of creatinine goes higher than a certain value.

>Before and after starting treatment with certain medicines. Some medicines occasionally cause kidney damage as a side-effect. Therefore, kidney function is often checked before and after starting treatment with certain medicines.

Other tests of kidney function

The routine kidney blood test is a general marker of kidney function. If the blood test is abnormal it cannot say what is causing the kidney problem. Therefore, if you have an abnormal result you may need further tests to find the cause of a kidney problem. For example: urine tests, other blood tests, scans, X-rays, kidney biopsy, etc.

Acute Kidney Injury

Acute kidney injury is a condition where your kidneys suddenly stop working properly. Usually this happens when you are unwell from another illness. If you have acute kidney injury you are often already ill in hospital. If not, you will usually be sent to hospital to be looked after. The earlier acute kidney injury is picked up, and the more carefully you are monitored, the better the chance of your kidneys recovering.

Acute kidney injury used to be called acute renal failure.

Understanding kidneys: where they are and what they do

The two kidneys lie to the sides of the upper part of the tummy (abdomen), behind the intestines, and either side of the spine. Each kidney is about the size of a large orange but bean-shaped.

A large artery - the renal artery - takes blood to each kidney. The artery divides into many tiny blood vessels (capillaries) throughout the kidney. In the outer part of the kidneys tiny blood vessels cluster together to form structures called glomeruli.

Each glomerulus is like a filter. The structure of the glomerulus allows waste products and some water and salt to pass from the blood into a tiny channel called a tubule. The liquid that remains at the end of each tubule is called urine. The urine then passes down a tube called a ureter which goes from each kidney to the bladder. Urine is stored in the bladder until it is passed out when we go to the toilet.

The main functions of the kidneys are to:

>Filter out waste products from the bloodstream, to be passed out in the urine.

>Help control blood pressure - partly by the amount of water passed out of the body as urine and partly by making hormones which are involved in blood pressure control.

>Make a hormone called erythropoietin, which stimulates the bone marrow to make red blood cells. This is needed to prevent anaemia.

>Control the amount of fluid in the body.

>Help keep various salts and chemicals in the blood at the right level.

What is acute kidney injury (AKI)?

If you have AKI your kidneys suddenly stop working as well as they should. This means the fluid, salts and chemicals in your body can rise or fall to abnormal levels and make you very ill. If there is too much acid, or there are too many salts, in your body your other organs can be affected. For example, your heart, lungs, brain, muscles, eyes, etc, can stop working properly. If the kidneys aren't getting rid of enough fluid, your body can become overloaded with it. This can cause swelling in your legs, or make it difficult to breathe.

It is different from chronic kidney disease (CKD) which is a much more gradual process which can happen over many years.

How common is acute kidney injury (AKI)?

In people who are unwell in hospital, AKI is common. Nearly as many as 1 in 5 people in hospital develop AKI. It is even more common in patients who are extremely unwell in intensive care units.

Who develops acute kidney injury (AKI)?

AKI is more common over the age of 65. People who have another serious illness and are in hospital are more likely to develop it. It may happen to people who are having operations, especially if they are older. It may happen to some people who are having a special X-ray with a dye (contrast) which contains iodine.

Some things make you more likely to develop AKI in these situations - for example:

>Being older.

>Having another illness like diabetes, heart failure or liver disease.

>Being dependent on a carer for fluids.

>Having a bad infection (for example, from a urinary infection, chest infection or skin infection).

>Some medicines - for example:
   -Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, diclofenac or naproxen.
    -Some blood pressure pills that work on the kidney.
    -Some antibiotics called aminoglycosides (such as gentamicin).
    -'Water tablets' (diuretics).

>Lacking in fluid in the body (being dehydrated).

>Another problem with your kidneys, such as CKD.

>Having had AKI before.

Children can develop AKI too. This is more likely if they have:

>Severe diarrhoea.

>A cancer of the blood cells.

>To rely on a parent or carer for fluids (more likely to become dehydrated).

>Low blood pressure.

>Another kidney illness such as nephritis.

>A severe infection.

What causes acute kidney injury (AKI)?

There are many things that can cause the kidneys to stop working properly. Sometimes it happens due to more than one cause.

Causes include:

>Severe infections.

>Blockage in the urinary system.

>Lack of fluid in the body (dehydration).

>Heavy bleeding (haemorrhage).

>Low blood pressure.

>Some medicines (see previous section for medicines that can harm the kidneys).

>Kidney diseases.

>The dye (contrast) that is used for some kinds of scans and X-rays.

What are the symptoms of acute kidney injury (AKI)?

There may be no specific symptoms of AKI. Often you already have symptoms of the illness that has caused AKI.

Symptoms that may happen include:

>Passing less urine than usual.

>Feeling sick or being sick (vomiting).

>Poor appetite.


>Swelling in the legs or other parts of the body.

How is acute kidney injury (AKI) diagnosed?

Your doctor would test for AKI with urine tests and blood tests. Your urine will be measured to see how much you are passing. In most people with AKI, this is less than normal. It will also be tested with a 'dipstick' to check for protein, blood cells and sugar, amongst other things. This will help work out the cause. You will have a blood test for a substance called creatinine. This is an indicator for how well the kidneys are working. Higher levels mean that the kidneys aren't getting rid of waste products as effectively as they should.

You may need an ultrasound scan to look for blockages in the urinary system. Ultrasound scans use sound waves to create a picture of the kidneys and urinary system.

You may also need other tests to try to find the cause for AKI. These might include other blood tests, scans or X-rays.

How is acute kidney injury (AKI) treated?

There isn't a specific medicine to treat AKI. The treatment will depend on the cause of AKI and the severity of the AKI.

The treatment is to carefully look after all the things the kidneys usually do. You will normally be in hospital and have blood and urine tests regularly. You may need extra or special fluid through a drip. You may be on a restricted diet to help get the balance of proteins and salts right. Any medicines which might be harming your kidneys would be stopped. The cause of the problem would be treated if this is possible. (For example, you might need antibiotics for an infection or surgery for any blockage if these were the cause.)

Your doctor will keep a close eye on the balance of minerals and salts in your body. You will have regular tests for potassium, sodium, calcium, sugar (glucose), phosphate and creatinine. You may need treatment with medicines or through a drip if the levels are not right.

Sometimes you need to have dialysis if medicines and fluids aren't working and you are becoming more ill. Dialysis is a procedure where your blood is passed through a machine to remove the waste products (as your kidneys would do if they were working). There are different ways this is done. How often it is done and how long each session lasts will depend on the way it is done. You would be referred to a kidney specialist or an intensive care specialist for this. In most people this can be stopped once the kidneys are working properly again.

These decisions would be made after discussion with you and explaining the options to you (and/or your relatives or carers where appropriate).

What is the outlook (prognosis)?

The outlook varies hugely. It depends on how bad kidney function becomes, who is looking after you, the cause of the problem and how ill you were to begin with.

The National Institute for Health and Care Excellence (NICE) has produced guidelines to try to cut the numbers of people who develop acute kidney injury (AKI) and who die because of it. The outlook is better if it is picked up earlier.

Many people who recover from AKI have normal kidney function afterwards. However, some go on to develop chronic kidney disease (CKD). Some need to keep having dialysis. If you have had AKI once, you are more likely to have it again in the future.

How can acute kidney injury (AKI) be prevented?

Prevention is certainly better than cure for AKI. Patients in hospital should be tested for AKI regularly. This is done by frequent blood tests and measuring how much urine they produce (and weight for children). People having scans or X-rays with a dye (contrast) should be checked to see how likely they are to develop AKI. If they are at risk, and if the test is really necessary, the chances of AKI are lower if these patients have a drip with extra fluid first. They should be regularly checked after the test.

Medicines which cause kidney damage should be avoided where it is possible. If they can't be avoided, the lowest possible dose should be used and tests done regularly to keep a check on how the kidneys are coping.

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