Pyelonephritis is an infection that can occur when bacteria from the bladder spread to the kidneys. In most cases, Escherichia coli (E. coli) bacteria cause the infection. Symptoms may include painful urination, frequent or intense urges to urinate, and back, side, or groin pain. The infection is diagnosed using urine tests; imaging tests may also be used to see stones, blockages, and swelling. Antibiotics are used to treat this condition.

What Is Pyelonephritis?

Pyelonephritis is a type of urinary tract infection (UTI) that develops when bacteria spread from the bladder to the kidneys. A serious health problem, pyelonephritis affects more women than men for reasons that are not yet well understood. Although pyelonephritis in men is not as common, it can be very serious when it does occur.

Understanding the Urinary Tract

The urinary tract consists of the kidneys, ureters, bladder, and urethra. The kidneys are two bean-shaped organs located below the ribs toward the middle of the back. The role of the kidneys is to:
  • Help control blood pressure
  • Make red blood cells
  • Keep bones strong
  • Remove extra water and wastes from the blood
  • Convert the wastes to urine.
The wastes in your blood come from the normal breakdown of active muscle and from the food that you eat. Your body uses the food for energy and self-repair and sends the wastes to the blood. If your kidneys did not remove these wastes, the wastes would build up in the blood and damage your body.
Narrow tubes called ureters carry urine from the kidneys to the bladder, which is an oval-shaped chamber in the lower abdomen. Like a balloon, the bladder's elastic walls stretch and expand to store urine and flatten back together when the urine is emptied through the urethra outside of the body.
Last reviewed by: Arthur Schoenstadt, MD
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