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Kidney infection (pyelonephritis)

Pyelonephritis is an infection of one or both of your kidneys. Anyone can get a kidney infection but it's most common in women and people who have an abnormal kidney.

You have two kidneys, which 'clean' your blood by filtering out water and waste products to make urine. Urine is stored in your bladder and then passed out of your body through your urethra. This is the tube that carries urine from your bladder and out of your body. 

Pyelonephritis is a bacterial infection of your kidneys. The infection can be either acute or chronic. Acute and chronic refer to how long the condition lasts, rather than how severe it is. This factsheet will focus on acute kidney infection, which tends to come on quickly but should go within a couple of weeks.

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An image showing the location of the bladder and surrounding structures


  • Symptoms Symptoms of kidney infection

    The symptoms of an acute kidney infection often develop quickly over a few hours or a day and may include:

    • pain in your lower back, abdomen (tummy) or side (it may be only on one side)
    • a fever
    • shivering and chills
    • feeling weak
    • feeling sick or vomiting
    • diarrhoea

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

    Around one in three women who get an acute kidney infection have symptoms of a bladder infection as well. This is also called cystitis, or a lower urinary tract infection (UTI). See our frequently asked questions for more information about UTIs.

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  • Diagnosis Diagnosis of kidney infection

    Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history. Your GP will ask you to provide a urine sample. He or she will usually do a 'dipstick' test to confirm if you have a urinary infection. Your GP may send your urine sample to a laboratory to find out which type of bacteria is causing the infection.

    In you have a severe kidney infection, your GP may recommend you go into hospital for further tests and treatment. Other tests may include:

    • a blood sample to see if you have signs of an infection
    • scans (such as a CT scan) to check for any problems or obstructions in your ureters or kidneys

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  • Treatment Treatment of kidney infection


    It’s important to drink enough fluids to prevent yourself from getting dehydrated. Make sure you get plenty of rest too.


    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.

    Your GP will usually prescribe antibiotics if he or she suspects that you have a kidney infection. It’s important to take the full course of antibiotics, even if your symptoms clear up before you finish them. Your symptoms should start to improve within a day or so. But if they get worse or you don't feel any better within 48 hours of starting treatment, contact your GP.

    Hospital treatment

    You may need hospital treatment if you’re:

    • pregnant
    • unable to keep down fluids or medicines
    • dehydrated
    • not responding to antibiotic treatment
    • diagnosed with blood poisoning (septicaemia)
    • at risk of developing complications

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


    You may need to have surgery if tests show that you have an obstruction (such as a kidney stone) in your ureters or kidneys.

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  • Causes Causes of kidney infection

    A kidney infection is usually caused by bacteria such as Escherichia coli (E. coli), which live in your bowel. The bacteria can get into your urinary tract if they spread from your anus to your urethra. The bacteria can enter your urethra and travel up into your bladder and will usually cause a lower UTI or cystitis. The bacteria can then travel up one or both of the tubes that connect your bladder to your kidneys (ureters) and cause a kidney infection.

    You can also spread the bacteria when you have sex, as bacteria can enter your urethra. Bacteria and viruses can also be carried in your blood from other parts of your body to your kidney.

    Women get more kidney infections than men. This is partly because the urethra is much shorter in women than in men. There is less distance for the bacteria to travel to the bladder.

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

    • have an abnormal kidney
    • have a blocked ureter or kidney, for example by a kidney stone or an enlarged prostate gland
    • are pregnant (see our frequently asked questions for more information)
    • have diabetes
    • have a weakened immune system, for example, if you have HIV/AIDS
    • have had a UTI in the past year
    • have urinary incontinence
  • Complications Complications of kidney infection

    An acute kidney infection can sometimes cause complications including:

    • a pocket of pus (abscess) in your kidney – this is called a pyonephrosis
    • your kidneys not working properly
    • blood poisoning (septicaemia) – this can happen if the bacteria that have caused your kidney infection get into your blood

    You're more likely to develop complications if you:

    • are pregnant
    • have type 1 or type 2 diabetes
    • are over 65
    • have a persistent kidney infection
    • have kidney disease
    • have a urinary catheter fitted (a tube that takes urine from your bladder out of your body)
    • have a weakened immune system – for example, if you have HIV/AIDS (which reduces your ability to fight infection)
  • Prevention Prevention of kidney infection

    If you often get a kidney infection or a UTI, your GP may advise you to take a low dose of antibiotics every day. How long you need to take them for will depend on your personal circumstances.

    You can also develop a kidney infection from cystitis. If you get cystitis, try self-help measures or get prompt treatment to cure the condition. This will reduce the risk of the infection spreading to your kidneys.

  • Kidney infection and pregnancy Kidney infection and pregnancy

    If you have a kidney infection when you're pregnant, it may lead to complications, such as:

    • kidney damage or even failure
    • having a baby with a low birth weight
    • premature labour
    • blood poisoning

    If your GP suspects you have a kidney infection, he or she may send you for tests and treatment in hospital.

  • FAQs FAQs

    Why is a kidney infection more common during pregnancy?


    During pregnancy your body undergoes physical changes that can affect how well it gets rid of urine. This can increase your risk of getting a bladder or kidney infection.


    As your baby grows, your womb (uterus) puts pressure on your bladder and the tubes that carry urine from your kidneys to your bladder (ureters). This can block the normal flow of urine to your bladder. This means that bacteria in the trapped urine can multiply and cause a kidney or bladder infection.

    Hormonal changes in pregnancy and the extra fluid in your bloodstream mean that your kidneys are having to worker harder. Your immune system, which usually defends your body against infections, also changes when you’re pregnant (to stop it attacking your baby). This means that a slight change in the normal functioning of your kidneys can increase your risk of having a urinary tract infection (UTI). This includes a bladder or kidney infection.

    Because of this you will be offered urine tests as part of your routine antenatal care. At each antenatal appointment, you will need to provide a urine sample. Your GP or midwife will test your urine for protein and bacteria. Protein in your urine can suggest poor kidney function and bacteria in your urine can suggest a UTI. It's important to provide this urine sample so you can get treatment for an infection early to prevent any problems with your pregnancy.

    If I have to go to hospital and I'm given antibiotic treatment through a drip in my arm, can I switch to antibiotic tablets?


    Yes, you should be able to switch to antibiotic tablets once you start to recover but it depends on your individual circumstances.


    You will usually only need to go into hospital if you have severe symptoms of a kidney infection, or you're pregnant. You may also need to go into hospital if you’re at particular risk of developing complications.

    In hospital, you may be given antibiotics and fluids through a drip into a vein (usually in your arm). The reason you’re given antibiotics in this way is so that they can enter your blood directly and reach the infection immediately. The quicker the antibiotics reach the infection, the quicker they can start to kill the bacteria. The sooner the infection starts to clear up, the sooner you will feel better.

    Your doctor may decide to switch to antibiotic tablets as your symptoms improve and you’re ready to go home. But this will depend on your individual circumstances and the type of antibiotic treatment you have.

    I have heard the terms 'upper UTI' and 'lower UTI'. What do these mean?


    Urinary tract infection (UTI) is the name given to an infection of any part of your urinary system. A lower UTI is an infection of your bladder and urethra (the tube that carries the urine from your bladder and out of your body). An upper UTI is an infection of your kidneys and your ureters (the tubes that carry urine from your kidneys to your bladder).


    Symptoms of a lower urinary tract infection may include:

    • a stinging or burning sensation when you pass urine
    • feeling that you need to urinate more often than usual
    • feeling that you need to urinate urgently even if you pass very little or no urine
    • urine that is cloudy, dark-coloured or has a strong smell
    • blood in your urine
    • pain or aching in your abdomen (tummy)

    If you have a healthy urinary tract, a UTI is unlikely to cause any serious damage to your kidneys. This is called uncomplicated infection.

    If you have an obstruction in your kidneys or urinary tract (such as kidney stones), this could be made worse by an infection. This is also the case if you have a condition that may affect your kidneys (such as type 1 diabetes). It can also cause serious damage to your kidneys and sometimes septicaemia (blood poisoning). This is called a complicated infection and you will need to go into hospital for treatment.

  • Resources Resources

    Further information


    • Acute pyelonephritis. Medscape., published 4 March 2013
    • Guidelines on urological infections. European Association of Urology., published 2013
    • Pyelonephritis. PatientPlus., published 22 April 2013
    • Kidney anatomy. Medscape., published 4 October 2013
    • Management of suspected bacterial urinary tract infection in adults. Scottish Intercollegiate Guidelines Network (SIGN)., published July 2012
    • Pyelonephritis (acute) in non-pregnant women. BMJ Clinical Evidence., published 13 January 2011
    • Pyelonephritis – acute. NICE Clinical Knowledge Summaries., published June 2013
    • Urinary tract infections in adults. National Kidney and Urologic Diseases Information Clearinghouse., published November 2011
    • Pyelonephritis: kidney infection. National Kidney and Urologic Diseases Information Clearinghouse., published 11 June 2012
    • Male urethra anatomy. Medscape., published 11 July 2013
    • Female urethra anatomy. Medscape., published 3 April 2012
    • Acute pyelonephritis – suspected. Map of Medicine., published 25 April 2013
    • Bacterial urinary tract infections. The Merck Manuals., published November 2013
    • Acute pyelonephritis – secondary care management. Map of Medicine., published 30 August 2011
    • Urinary tract infection in pregnancy. The Merck Manuals., published June 2013
    • The pregnancy book. Department of Health., published 2010
    • Mor G, Cardenas I. The immune system in pregnancy: a unique complexity. Am J Reprod Immunol 2010; 63(6):425–33. doi: 10.1111/j.1600-0897.2010.00836.x
    • Antenatal care. National Institute for Health and Care Excellence (NICE), March 2008.
    • Risk factors for complications during pregnancy. The Merck Manuals., published October 2013
    • Gupta K, Hooton TM, Naber KG, et al. International clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women: a 2010 update by the Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases. Clinical Practice Guidelines 2011; 52(5):e103–e20. doi: 10.1093/cid/ciq257
    • Lower urinary tract infection (UTI) in females. Map of Medicine., published 14 October 2013
    • Urinary tract infection in adults. PatientPlus., published 22 April 2013
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