Kidney infection (pyelonephritis)

Peer reviewed by Professor Raj Persad, Consultant Urological Surgeon
Next review due May 2019

An infection in your kidney is called pyelonephritis. When you have a kidney infection, you can feel generally unwell with a fever, sickness and back pain. How severe a kidney infection is can vary from mild to life-threatening. An infection can be acute (last for a short time) or chronic (last for a long time). The information we’re covering here is about acute kidney infection.

An image showing the location of the bladder and surrounding structures

About your kidneys

Your kidneys do a number of important jobs, including controlling your blood pressure and the amount of fluid in your body. They also 'clean' your blood by filtering out water and waste products to make urine. Urine is produced in your kidneys and passed down two tubes (called ureters) to be stored in your bladder. Urine is then passed out of your body through your urethra (the tube that carries the urine from your bladder and out of your body) when you go to the toilet.

Symptoms of kidney infection

The symptoms of a kidney infection vary from mild to severe. Symptoms can develop over a few hours or over the course of a day and may include:

  • pain in your back, abdomen (tummy) or sides (it may be only on one side)
  • fever (a high temperature)
  • feeling sick or vomiting (being sick)
  • confusion (in older people)

 You may also have symptoms of a lower urinary tract infection. This is an infection in your bladder and urethra and the symptoms may include:

  • blood in your urine
  • needing to go to the toilet to pass urine urgently and often
  • a burning or stinging feeling when you pass urine

If you have any of these symptoms, contact your GP.

Diagnosis of kidney infection

Your GP will talk to you about your symptoms and medical history. They will examine you and ask you to give a urine sample. The urine sample can be tested to see if you have an infection. This is sometimes called a 'dipstick' test. A urine sample may also be sent to a laboratory to find out which type of bacteria is causing the infection.

 If you have a severe kidney infection, you may go to hospital for more tests, including:

  • blood tests
  • scans, such as a renal ultrasound, or a scan called a CT urogram

A CT urogram is a type of X-ray that looks at your kidneys, bladder and ureters. Scans are used to check for any other problems such as blocked tubes or kidney stones.

Treatment of kidney infection


It’s important to stay well hydrated so make sure you drink plenty of fluids, like water. One way to tell if you’re hydrated is to check the colour of your urine – it should be pale-coloured. But some vitamins and medicines can affect the colour of your urine, so this might not always be the best way to check if you’re hydrated enough. If you feel tired and generally unwell, make sure you get plenty of rest.

Image showing hydration level by urine colour


If you need pain relief, you can take over-the-counter painkillers such as paracetamol. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

You will be given antibiotics to take if your GP thinks you have a kidney infection. You will probably need to take these for one to two weeks. It’s important to take the antibiotics as they have been prescribed, even if your symptoms clear up before you finish them. This helps to stop the infection from coming back.

Hospital treatment

If antibiotics haven’t begun to work within 24 hours of starting them, you may need to go into hospital for treatment. You may also need to go to hospital for treatment if you:

  • are pregnant
  • have a high fever
  • are being sick and can’t drink or take medicines
  • develop septicaemia (blood poisoning)
  • are at risk of developing complications or have other health problems such as diabetes or kidney disease

In hospital, you’re likely to need to have a drip inserted into a vein in your hand or arm to give you fluids and antibiotics.


If tests show that you have a blocked ureter or kidney, if you have a kidney stone for example, you may need an operation to remove it.

Causes of kidney infection

A kidney infection is sometimes caused by bacteria, such as Escherichia coli (E. coli) which usually live in your bowel. The bacteria can spread from your anus to your urethra, and then up to your bladder, ureters and kidneys. Bacteria can also get into your kidneys from your bloodstream.

You're more likely to develop a kidney infection if:

  • you have an abnormal kidney or urinary tract
  • you have a catheter (tube) that takes urine out of your body from your bladder
  • your ureter or kidney is blocked, for example by a kidney stone or an enlarged prostate gland
  • you’re pregnant
  • you have diabetes
  • your immune system is weakened, for example if you have HIV/AIDS
  • you have a urinary tract infection (UTI)
  • you have urinary incontinence

Complications of kidney infection

Kidney infections are usually uncomplicated and you should get better with treatment after a few days or weeks. However, sometimes an infection can become serious and even life-threatening. Complications include:

  • an abscess (a collection of pus) in your kidney
  • your kidneys not working properly, which can lead to kidney failure
  • scars, which are permanent, developing on your kidneys
  • septicaemia (blood poisoning) – this can happen if bacteria get into your blood

You're more likely to develop complications if you:

  • have a severe infection
  • have type 1 or type 2 diabetes
  • are over 65
  • have lots of kidney infections or a long-term infection
  • already have kidney disease
  • have a catheter (tube) that takes urine out of your body from your bladder   
  • have a weakened immune system – for example, if you have HIV/AIDS (which reduces your ability to fight infection)
  • have kidney stones

If you're pregnant and you develop a kidney infection, it can lead to complications for you and your baby. These include your baby being born early and being born small. If you have any of the symptoms of a kidney infection and you’re pregnant, you should see your GP or midwife as soon as possible.

Prevention of kidney infection

If you’re getting regular kidney infections or urinary tract infections (UTIs), your doctor may suggest you to take antibiotics over a longer period of time. How long you need to take them for will depend on your personal circumstances.

To help stop UTIs from developing you can try these self-help tips.

  • Drink more fluids, such as water.
  • Go to the toilet to pass urine as soon as you feel you need to go.
  • Go to the toilet to pass urine after you have sex.

Some people drink cranberry juice or take cranberry supplements to prevent UTIs. Cranberries have a substance in them that can stop bacteria from sticking to the walls of your bladder, and it’s thought this may help prevent a UTI. Overall, the research into this isn’t conclusive but it may be something you want to try to see if it helps. If you do, it’s suggested that high-strength supplements might be better than juice and more convenient to take.

Frequently asked questions

  • When you’re pregnant, your body goes through a lot of changes. This can affect how well it gets rid of urine and how easy it is for an infection to develop. This can increase your risk of getting a bladder or kidney infection.

    There are a number of reasons why you may be more likely to develop a kidney infection if you’re pregnant. Some of the main ones are listed below.

    • As your baby gets bigger, your uterus (womb) grows and pushes against your bladder and ureters (tubes that carry urine from your kidneys to your bladder). This can reduce the flow of urine and this can cause an infection.
    • There is more sugar in your urine, which can help bacteria to grow.
    • Changes in your hormones make it harder for your body to fight infections.

    You’ll be offered a urine test early on in your pregnancy to check for infection. If you have an infection, getting treatment quickly can help to prevent any problems with your pregnancy.

  • You might hear your GP or nurse use the term UTI, or urinary tract infection. It means an infection of any part of your urinary system – your kidneys, bladder, ureters or urethra.

    A lower UTI is sometimes called cystitis and is an infection in your bladder. An upper UTI is an infection of your kidneys and your ureters (the tubes that carry urine from your kidneys to your bladder).

    The symptoms of a lower urinary tract infection include cloudy, dark or strong smelling urine and problems passing urine. For example, you may pass small amounts of urine more often than usual, or find you need to get to the toilet very quickly (urgency). You may also find that when you do pass urine, it stings or burns, or it may have blood in it. Sometimes though, the symptoms may not be so obvious. For example, older people may feel confused, and young children may have a fever as the only symptom.

    If you have any of these symptoms, contact your GP.

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Related information

    • Acute pyelonephritis. BMJ Best Practice., last updated June 2016
    • Kidney anatomy. Medscape., updated October 2013
    • Acute pyelonephritis. Medscape., updated August 2015
    • Pyelonephritis. PatientPlus., last checked April 2016
    • Renal medicine and urology. Oxford handbook of General Practice (online). Oxford Medicine Online., published April 2014
    • Management of suspected bacterial urinary tract infection in adults. Scottish Intercollegiate Guidelines Network (SIGN), 2012.
    • Pyelonephritis – acute. NICE Clinical Knowledge Summaries., last revised June 2013
    • Jepson RG, Williams G, Craig JC. Cranberries for preventing urinary tract infections. Cochrane Database of Systematic Reviews 2012, Issue 10. doi:10.1002/14651858.CD001321.pub5
    • Urinary tract infections in pregnancy. Medscape., updated May 2015
    • Excellence (NICE), 2016.
    • Urinary tract infections in adults. PatientPlus., last checked April 2016
    • Urinary tract infections (lower) – women. NICE Clinical Knowledge Summaries., last revised July 2015
    • Urinary tract infection in children. PatientPlus., last checked April 2016
  • Reviewed by Natalie Heaton, Specialist Health Editor, Bupa Health Content Team, May 2016
    Peer reviewed by Professor Raj Persad, Consultant Urological Surgeon
    Next review due May 2019

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