Kidney infection (pyelonephritis)

Published by Bupa's Health Information Team, June 2010.

This factsheet is for people who have a kidney infection (pyelonephritis), or who would like information about it.

Pyelonephritis is an infection of one or both of your kidneys. Anyone can get it but it's most common in women, pregnant women are especially at risk.

About kidney infection

Most people have two kidneys. Your kidneys 'clean' your blood by filtering out water and waste products to make urine. The urine is stored in your bladder and then passed out of your body through your urethra.

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

Symptoms of kidney infection

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

• a high temperature (over 38°C)
  
• shivering (rigors)
  
• pain in your lower back (may be only on one side)
  
• feeling sick (nausea)
  
• vomiting

Around one in three people with acute kidney infection will also have symptoms of a bladder infection (cystitis or lower urinary tract infection, UTI). These symptoms may include:

• a stinging or burning sensation on passing urine
  
• the need to urinate more often than usual
  
• the need to urinate urgently even if very little or no urine is passed
  
• urine that is cloudy, dark coloured or has a strong smell
  
• blood in urine

These symptoms may be caused by problems other than a kidney infection. If you have any of these symptoms, see your doctor for advice.

Complications of kidney infection

Acute kidney infection can sometimes cause:

• a pocket of pus (abscess) in your kidney
  
• swelling (inflammation) of the kidney
  
• blood poisoning (sepsis) - this can happen if the bacteria causing the kidney infection get into your bloodstream

However, you are unlikely to get complications if your kidneys worked normally before you developed the infection. You are more likely to have complications, if you:

• are pregnant
  
• have diabetes
  
• are over 65
  
• have persistent kidney infection
  
• have a weak immune system (which reduces your ability to fight infection)
  
• have a urinary catheter fitted (a tube that takes urine from your bladder out of your body)

Sometimes, a kidney infection can cause severe damage and result in kidney failure, but this is rare.

Causes of kidney infection

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

Bacteria can enter the urethra from the surrounding skin of your genital area. Women are at greater risk of having a UTI partly because, in women, the urethra is nearer the anus (where bacteria from your bowel can collect). This makes it easier for bacteria to get transferred from the surrounding skin into the urethra. The urethra is also much shorter in women than in men, so there is less distance for the infection to travel to the bladder. For more information about cystitis, see related topics.

Sometimes a kidney infection can occur without a bladder infection. This can happen if a ureter or the kidney gets blocked, for example by a kidney stone or an enlarged prostate gland. The infection can also be carried to the kidneys from another part of your body in your bloodstream.

You are also more likely to develop a kidney infection, if you are pregnant, have diabetes or a weak immune system.

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. You will be asked to provide a urine sample. Your GP will usually do a 'dipstick' test to confirm a urinary infection and prescribe antibiotics. Your GP may send the urine sample to a laboratory to find out which type of bacteria is causing the infection, to ensure that suitable antibiotics are prescribed.

If your symptoms are severe or you are pregnant, your GP may refer you to a hospital for further tests and treatment. Other tests may include:

• a blood sample - this is usually only done if you have complications.
  
• X-rays or scans - to check for any problems or obstructions in your ureters or kidneys.

Treatment of kidney infection

Self-help

Drink enough fluids to stop dehydration; this is particularly important in pregnant women and people over 65.

Medicines

Over-the-counter painkillers such as paracetamol, ibuprofen and aspirin can reduce fever and ease pain and discomfort. 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. 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.

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, you should contact your GP.

Hospital treatment

You may need hospital treatment if you are:

• pregnant
  
• unable to keep down fluids or medicines
  
• dehydrated
  
• not responding to antibiotic treatment
  
• have other medical conditions such as diabetes

Surgery

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

Kidney infection and pregnancy

If you have a kidney infection during pregnancy, it may lead to complications, such as:

• kidney damage
  
• pre-eclampsia (high blood pressure in pregnancy)
  
• premature labour
  
• blood poisoning (sepsis)

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

Prevention of kidney infection

If you get kidney infection or a UTI 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 personal circumstances. Kidney infection can develop from cystitis. Getting prompt treatment for cystitis will reduce the risk of it spreading to your kidneys.

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.