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Pyelonephritis (kidney infection)

Pylonephritis is an infection of one or both of your kidneys. Anyone can get it but it's most common in women.

  • About pyelonephritis
  • Symptoms
  • Complications
  • Causes
  • Diagnosis
  • Treatment
  • Special considerations
  • Prevention
  • Sources
  • Related topics

About pyelonephritis

Most people have two kidneys. Your kidneys filter water and waste products from your blood, cleaning your blood and making urine. Urine drains into your bladder through tubes called ureters. When you pass urine, your bladder contracts, squeezing urine out of your body through a tube called the urethra.

Pyelonephritis is a bacterial infection of one or both of your kidneys. It can be either acute or chronic. This factsheet focuses on acute pyelonephritis. Acute and chronic refer to how long the condition lasts for, rather than how severe it is.


The symptoms of acute pyelonephritis often develop quickly (over a few hours to a day). Your symptoms may include:

  • a fever (over 37.5°C)
  • shivering
  • pain in the lower part of your back on either side
  • feeling sick
  • vomiting
  • diarrhoea

Around one in three people with acute pyelonephritis will also have symptoms of a lower urinary tract infection (cystitis). These can include:

  • a stinging or burning sensation when you pass urine
  • the need to urinate more often than you usually do
  • feeling the need to urinate urgently even if you pass very little or no urine
  • passing urine that is cloudy or dark coloured, which may have a strong smell
  • blood in your urine

Although not necessarily a result of pyelonephritis, if you have these symptoms you should see your doctor.


Acute pyelonephritis can sometimes cause:

  • an abscess (pus-filled area) in your kidney
  • inflammation (swelling) of the kidney
  • blood poisoning (septicaemia), which can occur if bacteria causing the pyelonephritis gets into your blood stream

However, you are unlikely to get complications if your kidneys worked normally before you developed pyelonephritis.

Pregnant women (see Special considerations) and people with diabetes are more likely to have complications.

Some people with chronic pyelonephritis develop severe kidney damage or kidney failure, but this is rare.


Pyelonephritis is a bacterial infection. It's usually caused by a bacterium called Escherichia coli (E. coli for short), which normally lives harmlessly in your bowel. The infection usually occurs when bacteria from your urethra and bladder travel up your ureters to your kidneys.

Bacteria can enter your urinary tract from the surrounding skin of your genital area and travel up towards your bladder, causing cystitis. Pyelonephritis usually occurs when the bacteria continue to travel up the urinary tract from the bladder and then into the ureters and kidneys. However, most people with cystitis don't go on to get pyelonephritis, as flow of urine usually stops the infection travelling up the urinary tract.

There are other causes of pyelonephritis but they aren't as common. Sometimes pyelonephritis can occur without a bladder infection. If your urinary tract or kidney gets blocked, for example by a kidney stone or an enlarged prostate, you are more likely to get pyelonephritis. This is because bacteria can then start to grow in the trapped urine. The infection can also be carried to the kidneys from another part of your body in your bloodstream.

You are more likely to develop pyelonephritis if you:

  • have an obstruction to your ureters or kidneys
  • are pregnant
  • have diabetes
  • have a weakened immune system (which reduces your ability to fight infection)


Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history. If your symptoms are severe, you have complications or you are pregnant (see Special considerations), your GP may refer you to a hospital for tests and treatment.

Most people don't need to go to hospital for pyelonephritis. Your GP can usually diagnose pyelonephritis and give you treatment.

Your doctor will also ask you for a urine sample. He or she may test your urine with a "dipstick" or may send the sample to a laboratory for more detailed tests. Your doctor may also ask you for a blood sample. These tests will find out which type of bacteria is causing the infection and helps your doctor decide which antibiotics would be most appropriate.

You may also need to have X-rays or scans to check whether there are any problems or obstructions in your ureters or kidneys.


Your GP will usually prescribe antibiotics immediately if he or she suspects that you have a kidney infection. The tests will let your doctor know if there is another antibiotic that would be more effective. You should always take the full course of antibiotics to get rid of the bacteria completely, even if your symptoms clear up before you finish the course.

Over-the-counter painkillers such as paracetamol, ibruprofen and aspirin can reduce a fever and can ease pain and discomfort. Follow the instructions in the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

If you have pyelonephritis, you should also drink plenty of fluids, at least two litres every 24 hours.

You should start to feel better after a day or so taking the antibiotics. But if your symptoms get worse or you don't feel any better after 24 hours, you should get advice from a doctor as soon as possible. You may need to go to hospital.

Hospital treatment

If you are in hospital, you may be given the antibiotics and fluids through a drip into a vein (usually in your arm).


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

Special considerations

If you are pregnant

If you have pyelonephritis when you are pregnant, you are more likely to get complications, such as:

  • your kidneys may stop working properly
  • you may have pre-eclampsia (causes high blood pressure)
  • you may go into labour and delivery before your due date
  • you may have breathing difficulties
  • you may get condition called septic shock, which is caused by a build up of toxins in the blood

If your GP suspects that you may have pyelonephritis and you are pregnant, he or she will probably send you for tests and treatment in hospital.


If you get pyelonephritis quite often, your doctor may advise you to take a low dose of antibiotics every day. How long you need to take them for will depend on your individual circumstances.

Pyelonephritis can develop from cystitis. Getting prompt treatment for cystitis will reduce the risk of it spreading to your kidneys. There are also a ways you can reduce your risk getting cystitis.


  • Pyelonephritis - acute. Clinical Knowledge Summaries, 2005. www.cks.library.nhs.uk
  • Car J. 2006; Urinary tract infections in women: diagnosis and management in primary care. BMJ 332:94
  • Chantel S. Everitt H. Kendrick T. Oxford Handbook of General Practice. 2nd ed. Oxford: Oxford University Press, 2005
  • Kumar and Clark M. Clinical Medicine. 6th ed. London: Elsevier Saunders, 2005
  • Kidney infection (pyelonephritis) Medline Plus. www.nlm.nih.gov/medlineplus, accessed 27 November 2007
  • Beers M et al (eds). The Merck Manual of Medical Information. 2nd ed. New York: Pocket Books, 2004

Related topics

  • Antibiotics
  • Cystitis
  • Diabetes - insulin dependent (type 1)
  • Diabetes - non-insulin dependent (type 2)
  • Kidney stones
  • Pre-eclampsia
  • X-ray