Kidney infection (pyelonephritis)

Expert reviewer, Professor Raj Persad, Consultant Urological Surgeon
Next review due February 2024

A kidney infection is called pyelonephritis. It often develops if you have a urinary tract infection (UTI) and bacteria travel up to one or both of your kidneys. A kidney infection can make you feel unwell, but is usually easily treated with antibiotics.

An image showing the location of the bladder and surrounding structures

About kidney infection

Your kidneys do a number of important jobs, such as 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 pee (urine).

Kidney infection (pyelonephritis) usually develops as a result of an infection in your lower urinary tract. Your urinary tract includes your kidneys, your bladder and your urethra (the tube that carries urine out of your body). Urinary tract infections normally start in your urethra. They can then travel to your bladder, causing an infection known as cystitis, and then up to your kidneys causing kidney infection.

You can also develop a kidney infection if bacteria get into your kidney from your bloodstream. This might be more likely to happen if something is blocking your urethra. This can happen if you have a kidney stone or in men who have an enlarged prostate.

Symptoms of a kidney infection

Kidney infection symptoms can develop quickly. Signs of kidney infection may include:

  • pain in your back or sides (it may be only on one side)
  • a fever (a high temperature) and chills
  • feeling sick or being sick
  • generally feeling unwell with flu-like symptoms

You may often notice symptoms of a lower urinary tract infection (cystitis) before developing a kidney infection. These may include needing to pee urgently, a burning or stinging feeling when you pee, and sometimes blood in your urine.

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

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Diagnosis of kidney infection

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

If you have a severe kidney infection (pyelonephritis) or your GP is unsure if you have a kidney infection, they may arrange extra tests. These may include:

Self-help for kidney infection

If you have a kidney infection (pyelonephritis), it’s important to make sure you keep hydrated by drinking enough fluids to prevent dehydration. The best thing to drink is water. One way to tell if you’re hydrated is to check the colour of your urine – it should be very pale yellow (straw-coloured).

Image showing hydration level by urine colour

It’s also important to get plenty of rest. Don’t try to do too much while you’re feeling unwell and recovering. You can take over-the-counter painkillers such as paracetamol or ibuprofen if you need help with any pain.

Treatment of a kidney infection


If urine tests show you have a kidney infection (pyelonephritis), your GP will prescribe antibiotics for you. You’ll probably need to take these for a week or two.

Most people with kidney infection respond well to antibiotics and make a good recovery. The time it takes for your infection to go depends on how severe it was to begin with – it can be days or weeks. It’s important to complete the full course of antibiotics, even if your symptoms clear up before you finish them. This helps to stop the infection from coming back.

Some people may need further treatment in hospital. Your GP will tell you when to go to hospital for kidney infection. You should contact your GP if your kidney infection symptoms get worse or don’t start to get better within 48 hours (two days) of starting the antibiotic.

Hospital treatment

Your GP may refer you to hospital for treatment if they think you’re at high risk of developing complications. This might be if you:

  • have signs of a more serious condition like sepsis (signs include a very high fever, shortness of breath and dizziness)
  • are pregnant
  • are significantly dehydrated or can’t drink or take medicines
  • have other underlying health problems such as diabetes or kidney disease
  • keep getting urinary tract infections (UTIs)

In hospital, you’ll probably have a drip put into a vein in your hand or arm to give you fluids and antibiotics. See our section on Complications below for more information on who may be more likely to need hospital treatment for a kidney infection.

Causes of kidney infection

The most common type of bacteria that causes kidney infections (pyelonephritis) is Escherichia coli (E. coli). There are also other types of bacteria that can cause it.

The bacteria travel from your urethra (the tube that carries urine out of your body) up to your bladder 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 underlying condition affecting your kidney or urinary tract
  • you have a catheter – a medical 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, cancer or are taking steroids
  • you have urinary incontinence
  • you have sex often or have had a new partner recently

Complications of kidney infection

In most people, kidney infection (pyelonephritis) clears up easily with treatment. But sometimes an infection can become serious and even life-threatening. Complications include the following.

  • Resistance to antibiotics. Your doctor may need to try a different antibiotic, and you may develop further infections.
  • An abscess (a collection of pus) in your kidney. You may need a procedure to drain it.
  • Damage to your kidney. This can be permanent and lead to kidney failure.
  • Sepsis (blood poisoning) – this can happen if bacteria get into your blood. If this happens, you’ll need to be admitted to hospital for treatment.

You're more likely to develop complications if you:

  • have a severe infection
  • have type 1 or type 2 diabetes
  • are over 65
  • have a long-term infection that’s not responding to treatment
  • have an underlying condition affecting your kidney or urinary tract
  • have a catheter (medical tube that takes urine out of your body from your bladder)
  • have a weakened immune system – for example, if you have HIV/AIDS or cancer
  • have kidney stones
  • are pregnant

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, contact your GP or midwife as soon as possible. This is really important even if your infection is mild.

Prevention of kidney infection

If you keep getting kidney infections (pyelonephritis) or urinary tract infections (UTIs), your doctor may sometimes prescribe antibiotics to help prevent them. How long you need to take them for will depend on your personal circumstances.

Kidney infections usually develop as a result of a lower UTI. To help stop UTIs from developing you can try these self-help tips.

  • Drink enough fluids to stay hydrated.
  • Don’t delay passing urine (peeing) – always go as soon as you feel the urge.
  • Go to the toilet to pee after you have sex.
  • Wipe from front to back after using the toilet, in order to avoid spreading bacteria from your anus.
  • Don’t ‘douche’ or use perfumed soaps and deodorants in your genital area.
  • If you have an enlarged prostate, try to make sure you completely empty your bladder when you pee.

There has been some research into whether D-mannose (a type of sugar) and cranberry products (such as cranberry juice or cranberry supplements) can prevent UTIs. There isn’t enough good evidence to say if these products are helpful for preventing UTIs, but some people think it’s worth giving them a try.

Frequently asked questions

  • Pyelonephritis is the medical name given to a kidney infection. Kidney infections are often caused if you have an infection in your lower urinary tract and the bacteria travel up to your kidneys. Kidney infection symptoms may include pain in your back or side, feeling sick or being sick, and a fever and chills. Treatment of a kidney infection is usually with antibiotics prescribed by your doctor.

  • If you have a kidney infection, symptoms can include:

    • pain in your back or sides
    • nausea (feeling sick)
    • vomiting (being sick)
    • a high temperature
    • shivering
    • flu-like symptoms, such as aches and pains in your muscles

    You may also need to pass urine (pee) more often, urgently and feel pain when you pee. For more information, see our section on Symptoms of a kidney infection above.

  • Most kidney infections are caused when bacteria get into your urethra (the tube that carries urine out of your body) and travel up through your urinary tract to your kidneys.

    It’s also possible to get a kidney infection if bacteria enter your kidneys from your bloodstream - because of an infection somewhere else in your body. There are certain factors that make you more likely to get a kidney infection. To find out more, see our section on causes of kidney infection above.

  • To find out if you have a kidney infection, your GP will ask you to provide a urine (pee) sample. This will be tested to see if you have an infection. Sometimes, your GP may need to arrange for you to have more tests. For more information on this, see our section on diagnosis of kidney infection above.

  • If you keep getting kidney infections (recurrent kidney infections), it’s often due to an underlying problem with your kidney or urinary tract. These might include the following.

    • Structural problems that you’re born with (congenital problems).
    • An enlarged prostate gland. This can mean your bladder doesn't empty properly. Urine left in your bladder can become infected and the infection can spread to your kidney.
    • Kidney stones.
    • Vesicoureteral reflux – a common problem in young children, when your urine goes the wrong way (from your bladder back towards your kidneys).

    Not finishing a course of antibiotics for kidney infection can also increase the chance of it coming back.

    Infections of your lower urinary tract (UTIs or cystitis) can lead to kidney infection, so talk to your GP if you keep getting UTIs. Your GP can talk you through measures you can take to reduce your risk of getting UTIs. They can also prescribe some medicines to help.

  • There are various 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 womb (uterus) grows and pushes against your bladder, which means it might not be able to empty properly. Bacteria are more likely to grow when the pee isn’t draining away properly.
    • Hormones cause the muscles to relax in your ureters (tubes that carry urine from your kidneys to your bladder), reducing the flow of urine. This may allow bacteria to grow.
    • There is more sugar in your urine, which can help bacteria to grow.

    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.

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Related information

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  • Reviewed by Pippa Coulter, Freelance Health Editor, February 2021
    Expert reviewer, Professor Raj Persad, Consultant Urological Surgeon
    Next review due February 2024