Name: Kidney Function Blood Test - U & E: What It Means and How to Prepare | Healthwords
Creator: Dr Roger Henderson
Published: 2021-05-11T09:01:17.673Z

You do not need to be fasting for this blood test, there are no special requirements. It can be taken like any normal blood test and is usually taken in a gold or yellow colour bottle. 

Remember to press hard for a good few minutes after the needle has been removed and keep your elbow straight, to prevent a nasty bruise!

Are there any special requirements for the blood test?

A kidney function blood test, also known as Urea and Electrolytes (U&E), is a common test that measures how well your kidneys are working and the balance of essential electrolytes in your body. Find out why you may need this test and what it involves.  Learn more with Healthwords.

Kidney Function Blood Test - U & E: What It Means and How to Prepare | Healthwords

The kidney function blood test is also known as urea and electrolytes, or U & E (doctors pronounce this "U's and E's"). It is one of the most commonly requested tests, and provides information on how the kidneys are functioning. It gives different markers of how well the kidneys are coping at filtering out waste products and also gives levels of some waste products.

Kidney function

This would be a normal test to order when doing some routine blood tests. Specifically, it will give your doctor information on how your kidneys are functioning at that point in time. Your kidneys are involved in processing many medications, and so it may need to be tested at certain intervals to ensure the medications are not causing any signs of damage to the kidneys.

It can monitor things with a sudden illness, such as [dehydration](https://www.healthwords.ai/article/dehydration-and-heatstroke) or sepsis that can put temporary stress on the kidneys - called [acute kidney injury](https://www.healthwords.ai/condition/acute-kidney-injury). It can also monitor kidney function if your kidneys have started to deteriorate with age or alongside other medical conditions, called [chronic kidney disease](https://www.healthwords.ai/condition/chronic-kidney-disease-424).

Why is my doctor ordering it?

Kidney cancer is one of the 10 most common cancers in the UK. Known medically as renal cancer, it is more common in men than women and it’s rare in people under the age of 50. Each year in the UK around 12,000 people are diagnosed with this type of cancer. 

There are several different types of kidney cancer but the commonest type is known as renal cell cancer. Others include transitional cell cancer, and Wilm’s tumours and clear cell sarcomas that only occur in children.  

You have two kidneys, one on either side of your tummy (your flanks) and slightly to the back. Their job is absolutely critical in keeping us alive - they balance up the salts (sodium, potassium and chloride) in our blood and excrete out any excess in urine. They filter out toxins into the urine and balance out fluids by making the urine more concentrated or more watery, depending on what we need. 

Signs that might alert you to a problem in the kidneys are blood in the urine or a lump in one of your flanks. It’s confirmed with blood tests, urine tests and scans. 

Blood tests have many different uses. They can be used to diagnose a condition, to monitor a particular organ in the body such as the kidney or liver, and they can also be used to give measurements of bodily processes such as the level of sugar in your blood or current levels of inflammation.

Acute kidney injury (AKI) means that the kidneys suddenly come under strain and they function less effectively. This can cause toxic waste products to build up in the blood and they change the balance of essential salts like potassium and sodium. It is essential it’s recognised and treated promptly, to ensure the kidneys have a chance to recover without permanent damage. It can prove life-threatening if left untreated.

AKI is diagnosed on a blood test, which will show that creatinine, a substance excreted by the kidneys, is raised, indicating the kidneys are not doing their job. Urea may also be raised, eGFR (estimated glomerular filtration rate) may be low, and potassium may be raised.

AKI is also known as acute renal failure. The name AKI is misleading in that it doesn’t mean you have received a physical injury or blow as such.

Dr Kandi - Acute Kidney Injury

Chronic kidney disease (CKD) means that the kidneys are not working to full capacity after damage from either advancing age or a disease process such as [diabetes](https://www.healthwords.ai/condition/diabetes-mellitus-300). You have two kidneys, and their function is to filter out waste products from the body via the urine and balance up certain salts like potassium and sodium in your blood.

CKD is sometimes referred to as renal failure, and is a long-term condition that usually causes no symptoms in the early stages.

It can get worse over time, but it usually progresses slowly over years, and it’s rare to progress to a stage where the kidneys stop working altogether, which requires dialysis. For this reason, CKD is monitored regularly and risk factors for further damage are carefully controlled, such as diabetes and [high blood pressure (hypertension)](https://www.healthwords.ai/condition/hypertension-what-is-it-358).

Blood in the urine is also known as haematuria. Blood that can be seen by the naked eye is called macroscopic haematuria, whereas blood that can’t be seen but is only found through a urine test is called microscopic haematuria. Although there are many harmless causes for it, both of these can indicate a cause for concern and require discussion with a doctor and possibly more investigations. 

Blood in the urine can occur alone with no other symptoms, but it can also occur with pain on peeing or the passage of clots. You may get other urine symptoms such as passing urine very frequently, needing to rush to the loo or the urine having a bad smell. The colour can vary from rose-coloured to Coca-Cola coloured. 

A urinary tract infection (UTI) is characterised by burning on passing urine, the urge to pass urine frequently and pain. Such infections occur when the normally sterile urine becomes infected with bacteria or other microorganisms. The most common bacteria causing a UTI is called *E.coli*, though other conditions such as Staphylococcus and [Chlamydia](https://www.healthwords.ai/condition/chlamydia-296) can also cause infection.

Such bacteria or organisms enter the urethra – the tiny tube that links from the vulva to the bladder – and cause irritation (urethritis). The infection can then spread back to the bladder causing [cystitis](https://www.healthwords.ai/article/cystitis-853) (inflammation of the bladder).

If a UTI is left untreated the infection can track even further back to the kidneys, via two small tubes called the ureters (one connects between each kidney and the bladder). This kidney infection is called pyelonephritis and can be a serious health problem.

With correct treatment, a urinary tract infection can be cleared quickly – in just one or two days. Even if symptoms are quickly alleviated, always finish any antibiotic course ordered by the doctor to ensure bacteria do not recur in a stronger or different form.

UTIs are much more common in women, than men because their urethra is very close to the vagina and anus so bacteria can spread easily. Women also have a shorter urethra than men which means bacteria can travel to the bladder quicker. Sexual intercourse can also irritate the urethra in a woman and increase the incidence of a UTI, and after the menopause UTIs can also become more common in women because of changes in the urethra, bladder and vagina due to hormonal fluctuations.

In men, UTIs can be indicative of prostrate problems, [kidney stones ](https://www.healthwords.ai/condition/kidney-stones)or a sexually transmitted disease ([STD](https://www.healthwords.ai/article/sti-am-i-at-risk)), and in the elderly UTIs can cause confusion and falls.

Kidney stones are crystals formed from the naturally occurring salts in urine that bulk together to form a solid lump. About 2% of adults have a kidney stone at any one time and usually affects people aged 30–60 years of age. Renal colic affects about 10–20% of men and 3–5% of women. There is often no obvious reason why they should occur. Kidney stones are stone-like lumps that can develop in one or both of the kidneys. The medical name for stones in the kidneys is nephrolithiasis, and if the stones cause severe pain, this is known as renal colic.

Waste products in the blood can occasionally form crystals that collect inside the kidneys. Over time, the crystals may build up to form a hard stone-like lump which the body then tries to pass out of the body in urine. This means it will often travel through the urinary system (the kidneys, kidney tubes and bladder). Kidney stones (also known as renal calculi or nephrolithiasis) can cause pain when they are stationary in the kidney itself, but the real problems occur if they move out from the kidney and into the pipe connecting the kidney and bladder (the ureter). If this happens, along with causing severe pain, they can block the pipe, leading to potential infection and difficulty passing urine. They carry the risk of preventing the kidneys working effectively, with immediate or long term consequences.

Symptoms vary widely and people often have kidney stones without realising it, suffering no symptoms. It only tends to be when kidney stones leave the kidney itself and begin to travel out of the body through the ureter (the tube that leads from each kidney to the bladder) that symptoms appear. This can be intense pain, felt in the side of the abdomen and down into the groin area, severe enough to cause vomiting, sweating and profound agitation. There may be [blood in the urine](https://www.healthwords.ai/symptom/blood-in-urine) and a need to pass water frequently, and symptoms can last from minutes to days. The size of the stone passed need not match the symptoms felt since a tiny stone the size of a grain of sand can be enough to trigger severe pain.

If you have classical-sounding pain, along with blood in your urine, your doctor may arrange a scan to see whether there is any evidence of kidney stones.

Blood tests have many different uses. They can help diagnose a condition, monitor a particular organ in the body such as the kidney or liver, and they can also be used to give measurements of bodily processes such as blood sugar or current levels of inflammation.

Blood tests have many different uses. Some of these include being used to diagnose a condition, to monitor a particular organ in the body such as the kidney or liver, and they can also be used to give measurements of bodily processes such as blood sugar, or current levels of inflammation.

Dr Roger Henderson

Chief Content Officer

Blood tests have many different uses. Some of these include being used to diagnose a condition, to monitor a particular organ in the body such as the kidney or [liver](https://www.healthwords.ai/article/liver-function-test-lft-blood-test), and they can also be used to give measurements of bodily processes such as [sugar levels in the blood](https://www.healthwords.ai/symptom/high-blood-sugar), or for levels of inflammation such as a [CRP](https://www.healthwords.ai/article/crp-blood-test-429) or [ESR blood test.](https://www.healthwords.ai/article/esr-blood-test-577)

Dr Kandi - Acute Kidney Injury (AKI)

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Kidney function blood test - U & E

Doctor’s advice

Kidney function

Why is my doctor ordering it?

Are there any special requirements for the blood test?

Related topics

Kidney cancer

ESR Blood Test

Acute Kidney Injury

Chronic Kidney Disease (CKD)

Blood in urine

Urinary Tract Infection (UTI)

Kidney stones

CRP Blood Test

Liver Function Test (LFT) Blood Test