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Understanding pyelonephritis

Acute pyelonephritis is a sudden and severe kidney infection. It causes the kidneys to swell and may permanently damage them. Pyelonephritis can be life-threatening. When repeated or persistent attacks occur, the condition is called chronic pyelonephritis. The chronic form is rare, but it happens more often in children or people with urinary obstructions.


Symptoms usually appear within two days of infection. Common symptoms include:

  • a fever greater than 102°F (38.9°C)
  • pain in the abdomen, back, side, or groin
  • painful or burning urination
  • cloudy urine
  • pus or blood in the urine
  • urgent or frequent urination
  • fishy-smelling urine

Other symptoms can include:

  • shaking or chills
  • nausea
  • vomiting
  • general aching or ill feeling
  • fatigue
  • moist skin
  • mental confusion

Symptoms may be different in children and older adults they are in other people. For example, mental confusion is common in older adults and is often their only symptom. People with chronic pyelonephritis may experience only mild symptoms, or they may even lack noticeable symptoms altogether.


The infection usually starts in the lower urinary tract as a urinary tract infection (UTI). Bacteria enter the body through the urethra and begin to multiply and spread up to the bladder. From there, the bacteria travel through the ureters to the kidneys.

Bacteria such as E. coli often cause the infection. However, any serious infection in the bloodstream can also spread to the kidneys and cause acute pyelonephritis.

Risk factors

Acute pyelonephritis

Any problem that interrupts the normal flow of urine causes a greater risk of acute pyelonephritis. For example, a urinary tract that is an unusual size or shape is more likely to lead to acute pyelonephritis. Also, women’s urethras are much shorter than men’s, so it’s easier for bacteria to enter their bodies. That makes women more prone to kidney infections and puts them at a higher risk of acute pyelonephritis.

Other people who are at increased risk include:

  • anyone with chronic kidney stones or other kidney or bladder conditions
  • older adults
  • people with suppressed immune systems, such as people with diabetes, AIDS, or cancer
  • people with vesicoureteral reflux (a condition where small amounts of urine back up from the bladder into the ureters and kidneys)
  • people with enlarged prostate

Other factors that can make you vulnerable to infection include:

  • catheter use
  • cystoscopic examination
  • urinary tract surgery
  • certain medications
  • nerve or spinal cord damage

Chronic pyelonephritis

Chronic forms of the condition are more common in people with urinary obstructions. These can be caused by UTIs, vesicoureteral reflux, or anatomical anomalies. Chronic pyelonephritis is more common in children than in adults.

Diagnosing pyelonephritis

Urine tests

A doctor will check for fever, tenderness in the abdomen, and other common symptoms. If they suspect a kidney infection, they will order a urine test. This helps them check for bacteria, concentration, blood, and pus in the urine.

Imaging tests

The doctor may also order X-rays or an ultrasound to look for cysts, tumors, or other obstructions in the urinary tract.

In people who do not respond to treatment within 72 hours, a CT scan (with or without injectable dye) may be ordered. This test can also detect obstructions within the urinary tract.

Radioactive imaging

A dimercaptosuccinic acid (DMSA) test may be ordered if your doctor suspects scarring as a result of pyelonephritis. This is an imaging technique that tracks an injection of radioactive material. A healthcare professional injects the material through a vein in the arm. The material then travels to the kidneys. Images taken as the radioactive material passes through the kidneys will show infected or scarred areas.

Treating pyelonephritis


Antibiotics are the first course of action against acute pyelonephritis. However, the type of antibiotic your doctor chooses depends on whether or not the bacteria can be identified. If not, a broad-spectrum antibiotic will be used. Although drugs can cure the infection within two to three days, the medication must be taken for the entire prescription period (usually 10 to 14 days). This is true even if you feel better.

The antibiotic options are:

Hospital admission

In some cases, drug therapy is ineffective. For a severe kidney infection, your doctor may admit you to the hospital. The length of your stay depends on the severity of your condition and how well you respond to treatment. Treatment may include intravenous hydration and antibiotics for 24 to 48 hours. While you’re in the hospital, doctors will monitor your blood and urine to track the infection. You’ll likely receive 10 to 14 days’ worth of oral antibiotics to take after you’re released from the hospital.


Recurrent kidney infections may result from an underlying medical problem. In those cases, surgery may be required to remove any obstructions or to correct any structural problems in the kidneys. Surgery may also be necessary to drain an abscess that doesn’t respond to antibiotics.

In cases of severe infection, a nephrectomy may be necessary. In this procedure, a surgeon removes part of the kidney.

Pyelonephritis in pregnant women

Pregnancy causes many temporary changes in the body, including physiological changes in the urinary tract. Increased progesterone and increased pressure on the ureters can result in an increased risk of pyelonephritis.

Pyelonephritis in pregnant women typically requires hospital admission. It can threaten the lives of both mother and baby. It can also increase the risk of premature delivery. Pregnant women are treated with beta-lactam antibiotics for at least 24 hours until their symptoms improve.

To prevent pyelonephritis in pregnant women, a urine culture should be conducted between the 12th and 16th weeks of pregnancy. A urinary infection that doesn’t have symptoms can lead to the development of pyelonephritis. Detecting it early can prevent kidney infection.

Pyelonephritis in children

According to the American Urological Association, UTIs are the second-most common reason for pediatric doctors' visits. Girls are at increased risk, especially if they’re younger than 1 year.

Children with UTIs often have fever, pain, and symptoms related to the urinary tract. A doctor should address these symptoms immediately before they can develop into pyelonephritis. Most children can be treated with oral antibiotics in an outpatient manner.

Potential complications

A possible complication of acute pyelonephritis is chronic kidney disease. If the infection continues, the kidneys may be permanently damaged. Although rare, it’s also possible for the infection to enter the bloodstream. This can result in a potentially deadly infection called sepsis.

Other complications include:

  • recurring kidney infections
  • the infection spreading to areas around the kidneys
  • acute kidney failure
  • kidney abscess

Preventing pyelonephritis

Pyelonephritis can be a serious condition. Contact your doctor as soon as you suspect that you have pyelonephritis or a UTI. This condition requires prompt medical attention, so the earlier you start treatment, the better.

Content licensed from:

Written by: Christine DiMaria, Matthew Solan and Ana Gotter
Medically reviewed on: Oct 11, 2016: Carissa Stephens, RN, CCRN, CPN

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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