Pyelonephritis (pie-low-ne-FRY-tis) is an infection in one or both kidneys. Pyelonephritis happens when urine (pee) infected with bacteria flows up from the bladder or when an infection in the bloodstream reaches the kidneys. More to Know A kidney infection like pyelonephritis is similar to a bladder infection, as they are both urinary tract infections (UTIs). However, children are usually sicker with fever, back pain, or vomiting with pyelonephritis. Keep in Mind Pyelonephritis requires medical attention. A doctor will ask for a urine sample, and may order other tests, to determine the cause and best treatment. It's important to treat kidney infections with a full course of antibiotics. Untreated and repeat infections can lead to high blood pressure and kidney disease in adulthood. All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts. Back to Articles Related Articles Urinary Tract Infections A urinary tract infection (UTI) is one of the most common reasons that teens visit a doctor. Learn about the symptoms of UTIs, how they're treated, and more in this article. Read More Movie: Urinary System Watch this movie about the urinary system, which produces pee. Read More Your Urinary System You pee every day, but what makes it happen? Find out in this article for kids about the urinary system. Read More Kidneys and Urinary Tract The kidneys perform several functions that are essential to health, the most important of which are to filter blood and produce urine. Read More Recurrent Urinary Tract Infections and Related Conditions Recurrent urinary tract infections can cause kidney damage if left untreated, especially in kids under age 6. Here's how to recognize the symptom of UTIs and get help for your child. Read More Urinary Tract Infections (UTIs) Urinary tract infections (UTIs) are common in kids. They're easy to treat and usually clear up in a week or so. Read More Your Kidneys You need at least one kidney to live. Find out why in this article for kids. Read More Kidneys and Urinary Tract The bean-shaped kidneys, each about the size of a child's fist, are essential to our health. Their most important role is to filter blood and produce urine. Read More Urine Tests Is your child having a urine culture or urinalysis performed? Find out why urine tests are performed, and what to expect when the doctor orders them. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.