Kidney Infection (Pyelonephritis)

Medically Reviewed by Minesh Khatri, MD on December 05, 2021
5 min read

A kidney infection, also called pyelonephritis, is when bacteria or viruses cause problems in one or both of your kidneys. It’s a type of urinary tract infection (UTI).

Your kidneys’ main job is to remove waste and take extra water from your blood. They’re part of your urinary tract, which makes liquid waste (urine) and removes it from your body. Like the exhaust system on your car, you want everything to work like it should so waste moves in one direction only: out.

Your urinary tract is made up of your:

  • Kidneys. These clean waste from your blood and make urine (your pee).
  • Ureters. These thin tubes, one for each kidney, carry urine to your bladder.
  • Bladder. This stores urine.
  • Urethra.  This tube carries urine from your bladder to outside your body.

If any of these parts gets germs in it, you can get a UTI. Most often, your bladder gets infected first. This can be painful but isn’t usually serious.

But if the bad bacteria or viruses travel up your ureters, you can get a kidney infection. If left untreated, a kidney infection can cause life-threatening problems.

Symptoms of a kidney infection include:

  • Blood or pus in your pee
  • Fever and chills
  • Loss of appetite
  • Pain in your lower back, side, or groin
  • Upset stomach or vomiting
  • Weakness or fatigue

You may also have some of the symptoms of a bladder infection, such as:

  • Burning or pain when you pee
  • A constant urge to pee, even soon after you empty your bladder
  • Cloudy or bad-smelling urine
  • Pain in your lower belly
  • Peeing much more often than usual

Call your doctor if you have these symptoms, especially if you have a bladder infection and you’re not getting better.

Kidney infections usually start with a bladder infection that spreads to your kidney. Bacteria called E. coli are most often the cause. Other bacteria or viruses can also cause kidney infections.

It’s rare, but an infection can also get in through your skin, make its way into your blood, and travel to your kidney. You can get an infection after kidney surgery, too, but that’s even more unlikely.

Anyone can get a kidney infection. But just as women get more bladder infections than men, they also get more kidney infections.

A woman’s urethra is shorter than a man’s, and it’s closer to their vagina and anus. That means it’s easier for bacteria or viruses to get into a woman’s urethra, and once they do, it’s a shorter trip to the bladder. From there, they can spread to the kidneys.

Pregnant women are even more likely to get bladder infections. This is because of hormone changes and because a baby puts pressure on the mother’s bladder and ureters and slows the flow of urine.

Any problem in your urinary tract that keeps pee from flowing as it should can raise your chances of a kidney infection, such as:

  • A blockage in your urinary tract, like a kidney stone or enlarged prostate
  • Conditions that keep your bladder from completely emptying
  • A problem in the structure of your urinary tract, like a pinched urethra
  • Vesicoureteral reflux (VUR), which is when pee flows backward from your bladder toward your kidneys

You’re also more likely to get an infection if you have:

After asking about your symptoms, your doctor will probably do tests including:

  • Urine analysis to check for blood, pus, and bacteria in your pee
  • Urine culture to see what kind of bacteria you have

Your doctor may also use these tests:

  • Ultrasound or CT. These look for a blockage in your urinary tract. Your doctor might do these if treatment doesn’t help within 3 days.
  • Voiding cystourethrogram (VCUG). This is a type of X-ray to look for problems in your urethra and bladder. Doctors often use these in children who have VUR.
  • Digital rectal exam (for men). Your doctor inserts a lubricated finger into your anus to check for a swollen prostate.
  • Dimercaptosuccinic acid (DMSA) scintigraphy. This uses a radioactive material to show kidney infection and damage.

If you don’t get treatment, a kidney infection can cause serious problems like:

  • Kidney damage. Pus might collect and create an abscess inside the kidney tissue. The bacteria may spread to other parts of your body. Your kidneys can also become scarred, which can lead to high blood pressure, chronic kidney disease, and kidney failure.
  • Blood poisoning (septicemia). When bacteria from a kidney infection get into your blood, they can spread through your body and into your organs. This is a medical emergency and needs treatment right away.
  • Severe infection. An infection called emphysematous pyelonephritis (EPN) may destroy kidney tissue and make toxic gas build up there. It usually happens in people who have diabetes.
  • Problems in pregnancy. Women who have kidney infections while pregnant are more likely to have babies born early or at a low weight. They’re also more likely to have kidney complications.

Your doctor will probably prescribe antibiotics, which you may need for a week or two. Your symptoms should improve within a few days, but make sure to take all of the medicine.

If you have a severe infection, you’ll need to stay in the hospital and get antibiotics intravenously (IV), through a needle.

If your kidney infections keep coming back, there might be a problem with the structure of your urinary tract. Your doctor may send you to a specialist, such as a urologist. These types of issues often need surgery.

You can do some things at home to feel better while you have an infection:

  • Drink plenty of fluids to flush out germs.
  • Get extra rest.
  • When you go to the bathroom, sit on the toilet instead of squatting over it, which can keep your bladder from completely emptying.
  • Take a pain reliever with acetaminophen. Don’t use aspirinibuprofen, or naproxen because these can raise your risk of kidney problems.
  • Use a heating pad on your belly, back, or side.

You can’t completely prevent bladder infections. But you may be less likely to get one if you:

  • Don’t use deodorant sprays or douches on your genitals.
  • Don’t use condoms or diaphragms with spermicide, which can trigger bacteria growth.
  • Use lubricated condoms. Other kinds can irritate the urethra, which makes infection more likely.
  • Drink lots of water.
  • Go to the bathroom as soon as you feel the urge.
  • Pee after having sex.
  • Wipe front to back after using the bathroom.