Kidney infections most often result from an infection in your urinary tract that spreads to one or both kidneys. Symptoms can include pus or blood in your urine and frequent urination, among others.

Kidney infections can be sudden or chronic. They’re often painful and can be life-threatening if not treated promptly. The medical term for a kidney infection is pyelonephritis.

Symptoms of kidney infection usually appear two days after infection. Your symptoms may vary, depending on your age. Common symptoms include:

  • pain in your abdomen, back, groin, or side
  • nausea or vomiting
  • frequent urination or the feeling that you have to urinate
  • burning or pain while urinating
  • pus or blood in your urine
  • bad-smelling or cloudy urine
  • chills
  • fever

Children under 2 years old with a kidney infection may have only a high fever. People over 65 may only have problems like mental confusion and jumbled speech.

If the infection is not treated promptly, symptoms could worsen, leading to sepsis. This can be life-threatening. Symptoms of sepsis include:

  • fever
  • chills
  • rapid breathing and heart rate
  • rash
  • confusion

You have two fist-sized kidneys in your upper abdomen, one on each side. They filter waste products out of your blood and into your urine. They also regulate the water and electrolytes contained in your blood. Kidney function is essential for your health.

Most kidney infections are caused by bacteria or viruses that enter the kidneys from the urinary tract. A common bacterial cause is Escherichia coli (E. coli). These bacteria are found in your intestine and can enter the urinary tract through the urethra. The urethra is the tube that carries urine out from your body. The bacteria multiply and spread from there to the bladder and kidneys.

Other causes of kidney infections are less common and include:

  • bacteria from an infection somewhere else in your body, such as from an artificial joint, that spreads through your bloodstream to the kidneys
  • surgery of the bladder or kidneys
  • something blocking urine flow, such as a kidney stone or tumor in your urinary tract, an enlarged prostate in men, or a problem with the shape of your urinary tract

Anyone can get a kidney infection, but here are some factors that make it more likely:

  • Urinary tract infections (UTIs). About 1 out of 30 UTIs leads to a kidney infection.
  • Being female. Women are more at risk than men for kidney infections, because the urethra is shorter than it is in men. This makes it easier for bacteria to reach the urinary tract. Also, the urethra in women is closer to the vagina and anus, which allows bacteria to spread more easily to the urinary tract.
  • Pregnancy. The urinary tract shifts in pregnancy and may make it easier for bacteria to get to the kidneys.
  • Weakened immune system. This includes people with diabetes, HIV or AIDS, and those taking drugs that suppress the immune system.
  • Damage to the spinal cord or nerve damage to the bladder. This could keep you from noticing the signs of a UTI that might lead to kidney infection.
  • Problems emptying your bladder completely. This is called urinary retention. It can also occur in people with spina bifida or multiple sclerosis.
  • Use of a catheter to drain your urine.
  • Urine backup. This is when your urine backs up to one or both of your kidneys, instead of the normal one-way outflow. It’s called vesicoureteral reflux, and it occurs most commonly in children.
  • Problems with the shape of your urinary tract.
  • Examination of the bladder with an instrument called a cystoscope.


There are few statistics on the incidence of kidney infections. A 2007 study reported that for females, there were 12-13 outpatient cases and 3-4 inpatient cases per 10,000 females. The numbers were lower for males, with 2-3 outpatient cases and 1-2 inpatient cases per 10,000 males. The highest incidence was among young women, and next were infants and older adults.

If you have bloody urine or if you suspect a kidney infection, see your doctor. You should also see your doctor if you have a UTI and your symptoms aren’t improving with treatment.

Your doctor will ask you questions about your medical history and symptoms. They will also ask about any risk factors you might have and do a physical examination.

Some of the tests the doctor may use include:

  • A rectal examination for males. This may be done to check whether the prostate is enlarged and blocking the bladder neck.
  • Urinalysis. A urine sample will be examined under a microscope for bacteria and also white blood cells, which your body produces to fight infection.
  • Urine culture. A urine sample will be cultured in the laboratory to determine the specific bacteria that grow.
  • A CT scan, MRI, or ultrasound test. These provide images of your kidneys.

Your treatment will depend on the severity of your kidney infection.

If the infection is mild, oral antibiotics are the first line of treatment. Your doctor will prescribe antibiotic pills for you to take at home. The type of antibiotic may change once the results of your urine tests are known to something more specific to your bacterial infection.

Usually you’ll need to continue taking antibiotics for two or more weeks. Your doctor may prescribe follow-up urine cultures after your treatment to make sure the infection is gone and has not returned. If necessary, you may get another course of antibiotics.

For a more serious infection, your doctor may keep you in the hospital to receive intravenous antibiotics and intravenous fluids.

Sometimes surgery may be necessary to correct a blockage or problematic shape in your urinary tract. This will help prevent new kidney infections.

You should feel better within a few days of taking antibiotics. Be sure to finish the entire course of antibiotics the doctor prescribed so that your infection doesn’t return, however. The usual course of antibiotics is two weeks.

A history of UTIs may put you at risk for future kidney infections.

To relieve discomfort from the infection:

  • Use a heating pad on your stomach or back to help reduce pain.
  • Take over-the-counter (OTC) pain medication, such as acetaminophen (Tylenol). Your doctor may also prescribe pain medication if OTC medications don’t help your symptoms.
  • Drink 6-8 eight-ounce glasses of water a day. This will help flush out the bacteria in your urinary tract. Coffee and alcohol might increase your need to urinate.

If your infection is untreated or poorly treated, there can be serious complications:

  • You may permanently damage your kidneys, leading to chronic kidney disease or, rarely, kidney failure.
  • Bacteria from your kidneys could poison your bloodstream, causing life-threatening sepsis.
  • You may develop renal scarring or high blood pressure, but this is rare.

If you’re pregnant and have a kidney infection, this increases the risk of your baby having low weight.

If you’re in general good health, you should recover from a kidney infection without complications. It’s important to see your doctor at the first signs of a kidney infection so that treatment can start right away. That can help reduce your risk for complications.

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