21 / 03 / 2021

Graciano Masauso answers questions about kidney disease

The kidneys are complex organs that control blood chemistry, blood pressure and the amount of fluid in the body.

What do the kidneys do?

The kidneys are highly complex organs that control substances in the blood, blood pressure, and the amount of fluid in the body. They also keep the blood clean and chemically balanced.

Acting as very efficient and specialised filters, they work to rid the body of waste and toxic substances and return vitamins, amino acids, glucose, hormones and other vital substances into the bloodstream.

Where are the kidneys?

Most people have two kidneys, which sit deep in the abdomen (behind the liver and intestines) in the small of the back, either side of the spine.

Shaped like a bean, each kidney weighs anywhere between 40 grams to 190 grams depending on gender and can very between left and right kidney. A kidney is about 10-15cms long.

Many people are able to lead healthy and active lives with just one functioning kidney. Some may have been born with one kidney, others may have had a kidney removed due to illness or injury and some people may have donated one of their kidneys to someone with kidney failure (in a kidney transplant operation).

What do kidneys do?

The kidneys have a number of important functions:

  • Their main job is to filter the blood to remove ‘waste products’ that the body doesn’t need, and to keep the amount of water in the body constant. The excess fluid and the waste products form urine.
  • They also secrete a number of essential hormones which:
    • help to regulate blood pressure by sending out signals to other parts of the body that control blood vessel contraction
    • keep our blood in a neutral non-acid state
    • stimulate red cell production from our bone marrow
    • ‘activate’ the Vitamin D we obtain from our diets and sunlight to help to keep our bones and muscles healthy.

Our kidneys must maintain these delicate balances in order to ensure that all the cells in our bodies can function properly.

Key kidney components

Around one quarter of all the blood flow leaving the heart goes to the kidneys. The blood is then channelled to about a million tiny filters in each kidney. The filters are called glomeruli. These are joined onto small tubes (tubules) to form nephrons (the structural and functional units of the kidney).

Each day around 180 litres of this filtered blood (known as filtrate) pass into the nephrons. Nearly all of the liquid is then reabsorbed back into the bloodstream: between one and one-and-a-half litres is sent out of the body as urine.

This vital process ensures that the body functions efficiently.

Sometimes kidneys do not work properly for a wide variety of reasons; some of them not yet fully understood. That’s why scientists are constantly seeking new ways to investigate and solve the many complexities of the kidney.

Make an appointment to see your GP if you think there may be something wrong with your kidney function or have any of the symptoms associated with possible kidney problems. You can find lots of helpful tips and advice about planning your visit, including what questions to ask, in our visiting your doctor section.

How is kidney disease measured and divided into stages?

Kidney disease is measured and categorised using a blood test which gauges the eGFR (estimated glomerular filtration rate) and a urine test which shows the ACR (urine albumin:creatinine ratio).

Glomerular filtration rate: GFR and eGFR

The main function of the kidneys is to clear water-soluble waste products (such as creatinine) from the blood. The efficiency of clearance is measured using the GFR

  • The GFR (glomerular filtration rate) is a measure of how much blood (in millilitres) is ‘cleaned’ by the kidneys in one minute. By using a blood test to measure creatinine levels we can calculate the estimated GFR, known as eGFR. We do this using a formula that takes body size into account. The average adult body size is 1.73 m2. A normal GFR is around 100 ml/min/1.73m2
  • Because the average normal eGFR is 100, the eGFR can be seen as a percentage of normal kidney function. However, values as low as 60 are considered normal if there is no other evidence of kidney disease
  • The eGFR is used to calculate the ‘G stage’ of CKD (as indicated in the Stages of CKD chart)
  • The eGFR calculation can be inaccurate in people who have much more, or much less muscle than average people of their age, sex, and ethnic origin. For instance, it can be falsely low in body builders, and falsely high in people with anorexia nervosa.

Albuminuria: the urine albumin:creatinine ratio

A simple urine test called the urine Albumin:Creatinine ratio (ACR) is also performed to look for signs that protein is leaking into the urine (a condition called albuminuria or proteinuria). This is an important sign of kidney damage. The ACR is used to calculate the ‘A stage’ of CKD (as indicated in the Stages of CKD chart below).

There are three recognised stages of albuminuria:

  • A1 – normal to mildly increased urine protein levels (lower than 3mg/mmol)
  • A2 – moderately increased urine protein levels (between 3-30mg/mmol)
  • A3 – severely increased urine protein levels (higher than 30mg/mmol)

Combining your ACR ratio with your eGFR can help doctors try to predict whether your kidney disease is likely to progress and whether you are more likely to develop complications such as heart and circulatory problems. Other factors are also taken into account, e.g. age. In general, the higher the ‘A’ stage, the more likely it is that you will benefit from blood pressure-lowering treatment.

Explaining the stages of kidney disease

This chart shows the stages of kidney disease and outlines how disease is likely to progress if kidney function reduces and urine protein levels increase.

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What happens when kidneys go wrong?

Kidneys can develop abnormalities or stop working properly for many reasons. Issues can often be caused by other conditions putting a strain on them. The general term for kidney problems is kidney disease.

What is kidney disease?

Kidney disease is a term used by doctors to include any abnormality of the kidneys, even if there is only very slight, temporary damage – for example if someone gets a urinary infection.

If a person’s kidney damage is more likely to be permanent and possibly progressive it is known as chronic kidney disease (CKD) – where ‘chronic’ means ‘longer-lasting’, rather than ‘severe’. The condition is broken down into various stages, depending on the level of kidney damage and the percentage of kidney function left.

Sometimes people’s kidneys can suddenly develop problems. This is known medically as acute kidney injury (AKI). Where ‘acute’ means ‘sudden’, rather than referring to levels of severity and ‘injury’ means ‘any form of upset’, which doesn’t necessarily have to be a physical injury.

Kidney disease is extremely common. In fact, one in ten of us may have some reduction in kidney function. But far fewer than one in ten of those affected will develop kidney failure requiring dialysis or a kidney transplant.

People with kidney disease are more prone to have high blood pressure and potential problems with circulation so it’s always a good idea to have regular health checks so that people can be offered lifestyle advice and treatment to protect the kidneys from future damage and to reduce the risk of stroke and heart attack.

How kidney disease can affect the body

Kidney disease can affect the body in a number of different ways:

Kidney damage and high blood pressure
The kidneys help to regulate blood pressure by controlling the amount of fluid in the circulation and by sending chemical messengers (called ‘hormones’) that control constriction of blood vessels. Many forms of kidney damage can cause high blood pressure. High blood pressure can also contribute to progressive kidney damage, so this can be a ‘vicious cycle’.

Erythropoietin is another hormone that is secreted by the kidney, and acts on the bone marrow to increase the production of red blood cells by the bone marrow. If kidney function diminishes, insufficient hormone is produced and the number of red blood cells being produced will fall, resulting in anaemia – a low blood count.

Bone and muscle weakness
Healthy kidneys ‘activate’ Vitamin D (which we get from some food and from sunlight). The active form of Vitamin D is needed to maintain normal bone structure and effective muscle function. Advanced kidney disease reduces the amount of activated vitamin D in the system. This can cause bone disease, increasing the risk of fractures and bone pain; and can sometimes cause muscle weakness.

Kidney disease is varied and complex, with many types of conditions, treatments and scales of illness (ranging from temporary, minor ailments to those that are life-threatening).

Am I at risk?

Around 3 million people in the UK are at risk of chronic kidney disease (CKD) – where, in general, kidney damage is potentially long-lasting and possibly progressive, rather than severe.

Often there are few, if any symptoms and many people are not aware they have the condition.

Risk factors

Kidney disease (a term used by doctors to include any abnormality of the kidneys) can affect anyone at any age. However, certain factors may mean that you are at greater risk of developing the illness:


High blood pressure*

Cardiovascular disease (conditions affecting the heart or blood vessels.)

Family history of kidney disease

If you are from a Black, Asian or minority ethnic background


Being overweight or obese

Use of cocaine, heroin, and other ‘hard drugs’

*It is more common if your blood pressure or diabetes hasn’t been well controlled.

What are symptoms of kidney disease?

Most people with early kidney disease don’t have any symptoms at all, and so don’t know that there’s anything wrong with their kidneys. More advanced kidney disease can cause a range of symptoms, although none of these symptoms occur only in kidney disease.

What are the symptoms in more advanced kidney disease?

People with more advanced kidney disease can experience a range of physical and emotional symptoms.

Symptoms can include:

  • tiredness and lack of energy
  • dry skin
  • itching
  • difficulty sleeping
  • poor appetite and weight loss
  • decreased interest in sex and/or difficulty becoming sexually aroused
  • bone or joint pain
  • muscle cramps
  • restless legs
  • swollen ankles, feet or hands caused by water retention (oedema)
  • feeling sick
  • dizziness or light-headedness
  • finding it difficult to concentrate
  • feeling sad, irritable or anxious
  • headaches
  • shortness of breath

Speak to your doctor if you have any of these symptoms

The symptoms of kidney disease can be caused by other less serious conditions, but it’s still important to get them checked out by your GP. If a kidney problem is detected, depending on the problem, early diagnosis and treatment can help to slow down any damage. Your GP will use blood and urine tests to check for kidney disease.