Inflammation of one or both kidneys, usually due to bacterial infection
Pyelonephritis is one of the most common kidney disorders, particularly in young and middle-aged adults. In this condition, one or both of the kidneys become inflamed, usually as a result of a bacterial infection. In adults, pyelonephritis causes intense pain around the kidneys. The condition can usually be promptly diagnosed and treated and, for this reason, rarely leads to long-term damage to the kidneys. However, the symptoms of pyelonephritis may be less obvious in children. As a result, it may go unnoticed and lead to serious kidney damage (see Urinary tract infections in children), sometimes resulting in kidney failure in later life.
Pyelonephritis may be caused by bacteria entering the urinary tract through the urethra (the passage from the bladder to the outside of the body). Often the bacteria ascend to the kidneys through the ureters from an infection in the bladder (see Cystitis). Urinary infections, and therefore pyelonephritis, are much more common in females because the female urethra is shorter than that of the male, and its opening is nearer the anus. Bacteria from the anal area may enter the urethra during sex or if the area is wiped from back to front after a bowel movement. People with diabetes mellitus are more likely to have urinary infections, partly because glucose in the urine may encourage bacterial growth.
In both sexes, pyelonephritis is more likely to develop if there is a physical obstruction anywhere in the urinary tract that prevents the normal flow of urine. In these circumstances, if bacteria have already contaminated the urine, they will not be flushed through the urinary tract as normal. Instead, they multiply in the stagnant urine. Obstruction to urine flow may result from pressure on the urinary tract. Common causes of blockage include the expanding uterus in pregnant women or an enlarged prostate gland in men. Normal urine flow may also be obstructed by bladder tumours or kidney stones. In addition, kidney stones may harbour bacteria and can therefore predispose to infection in the urinary tract. All of these conditions may lead to recurrent episodes of pyelonephritis.
Bacteria may also enter the bladder during bladder catheterization, a procedure in which a tube is passed up the urethra into the bladder to drain urine. In addition, bacteria may be carried in the bloodstream from elsewhere in the body to the kidneys.
The symptoms of pyelonephritis may appear suddenly, often over a period of a few hours, and include:
Intense pain that begins in the back just above the waist and then moves to the side and groin.
Fever over 38°C (100°F), resulting in shivering and headache.
Painful, frequent passing of urine.
Cloudy, bloodstained urine.
Nausea and vomiting.
If you develop these symptoms, consult your doctor immediately.
If your doctor suspects pyelonephritis, he or she will probably examine a sample of your urine to find out whether it contains bacteria. If there is evidence of infection, the urine sample will be sent for laboratory analysis to establish which type of bacterium has caused the infection. Men and children may need further tests to detect an underlying cause after a single episode of the disorder. Pyelonephritis is more common in women. For this reason, further tests are carried out for women only if they have recurrent episodes, or if the doctor suspects an underlying cause.
Further investigations may include a blood test to assess the function of the kidneys. Imaging procedures, such as ultrasound scanning, CT scanning, or intravenous urography, may also be carried out to check for signs of kidney damage or a disorder such as kidney stones.
Pyelonephritis is usually treated with a course of oral antibiotics, and symptoms often improve within 2 days of treatment. When the course of antibiotics is finished, further urine tests may be carried out to confirm that the infection has cleared up. However, if you are vomiting, in pain, or seriously ill, you may be admitted to hospital and given intravenous fluids and antibiotics.
If you experience repeated episodes of pyelonephritis, you may be advised to take low-dose antibiotics for a period of 6 months to 2 years to reduce the frequency of the attacks. If you have an underlying disorder, such as kidney stones, this may also need to be treated.
In most cases, prompt treatment of pyelonephritis is effective, and the condition causes no permanent damage to the kidneys. However, rarely, frequent episodes of pyelonephritis may lead to scarring of the kidneys and result in irreversible damage (see End-stage kidney failure).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.